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Rocks and Minerals - Britannica Illustrated Science Library, Manuais, Projetos, Pesquisas de Geologia

Rochas e minerais, Livro britanico

Tipologia: Manuais, Projetos, Pesquisas

2011

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Baixe Rocks and Minerals - Britannica Illustrated Science Library e outras Manuais, Projetos, Pesquisas em PDF para Geologia, somente na Docsity! Britannica Illustrated Science Library OS About the pagination of this eBook Due to the unique page numbering scheme of this book, the electronic pagination of the eBook does not match the pagination of the printed version. To navigate the text, please use the electronic Table of Contents that appears alongside the eBook or the Search function. For citation purposes, use the page numbers that appear in the text. Rocks and Minerals Contents PHOTOGRAPH ON PAGE 1A stone with a blue opal in itscenter is a product of time, since it forms over millions of years. Dynamics of the Earth's Crust Page 6 Formation and Transformation of Rocks Page 40 Use of Rocks and Minerals Page 76 Minerals Page 18 Classes of Rocks Page 60 R ocks, like airplane flight recorders, store in their interior very useful information about what has happened in the past. Whether forming caves in the middle of mountains, mixed among folds, or lying at the bottom of lakes and oceans, stones are everywhere, and they hold clues to the past. By studying rocks, we can reconstruct the history of the Earth. Even the most insignificant rocks can tell stories about other times, because rocks have been around since the beginning of the universe. They were part of the cloud of dust and gases that revolved around the Sun over four billion years ago. Rocks have been silent witnesses to the cataclysms our planet has experienced. They know the cold of the glacial era, the intense heat of the Earth's interior, and the fury of the oceans. They store much information about how external agents, such as wind, rain, ice, and temperature changes, have been altering the planet's surface for millions of years. F or ancient civilizations, stones symbolized eternity. This idea has persisted throughout time because stones endure, but they are recycled time and again. Fifty million years from now, nothing will be as we now know it—not the Andes, nor the Himalayas, nor the ice of Antarctica, nor the Sahara Desert. Weathering and erosion, though slow, will never stop. This should free us from any illusion of the immortality of the Earth's features. What will everything be like in the future? We don't know. The only sure thing is that there will be rocks. Only stones will remain, and their chemical composition, shape, and texture will provide clues about previous geological events and about what the Earth's surface was like in the past. In the pages of this book, illustrated with stunning images, you will find invaluable information about the language of rocks and natural forces in general. You will also learn to identify the most important minerals, know their physical and chemical properties, and discover the environments in which they form. D id you know that the Earth's crust and its oceans are sources of useful and essential minerals for human beings? Coal, petroleum, and natural gas found in the crust allow us to travel and to heat our homes. Furthermore, practically all the products that surround us have elements provided by rocks and minerals. For example, aluminum is used to produce beverage cans; copper is used in electric cables; and titanium, mixed with other durable metals, is used in the construction of spacecraft. We invite you to enjoy this book. It is full of interesting and worthwhile information. Don't miss out on it! Memory of the Planet THE MONK'S HOUSE This orthodox monk lives in a volcanic cave, very close to the 11 Christian churches located in the Ethiopian town of Lalibela. ROCKS AND MINERALS 11 Mesozoic THE ERA OF REPTILES Triassic 251 Cenozoic THE AGE OF MAMMALS Paleogene Paleocene Eocene 65.5 Jurassic 199.6 Cretaceous 145.5 Neogene Miocene 23.03 Pleistocene Holocene Africa separates from South America, and the South Atlantic Ocean appears. Proliferation of insects Appearance of dinosaurs The first mammals evolve from a group of reptiles called Therapsida. Birds emerge. The dinosaurs undergo adaptive radiation. North America and Europe drift apart. North and South America are joined at the end of this time period. The formation of Patagonia concludes, and an important overthrust raises the Andes mountain range. The heat caused by the expansion of fragments from the impact together with the greenhouse effect brought about by the spreading of ashes in the stratosphere provoked a series of climatic changes. It is believed that this process resulted in the extinction of the dinosaurs. The African Rift Zone and the Red Sea open up. The Indian protocontinent collides with Eurasia. Gondwana reappears. IMPACT FROM THE OUTSIDE It is believed that a large meteor fell on Chicxulub, on the Yucatán Peninsula (Mexico), about 65 million years ago. The impact caused an explosion that created a cloud of ash mixed with carbon rocks. When the debris fell back to Earth, some experts believe it caused a great global fire. THE LAST GLACIATION The most recent period of glaciation begins three million years ago and intensifies at the beginning of the Quaternary period. North Pole glaciers advance, and much of the Northern Hemisphere becomes covered in ice. HUMAN BEINGS APPEAR ON EARTH. Although the oldest hominid fossils (Sahelanthropus) date back to seven million years ago, it is believed that modern humans emerged in Africa at the end of the Pleistocene. Humans migrated to Europe 100,000 years ago, although settling there was difficult because of the glacial climate. According to one hypothesis, our ancestors reached the American continent about 10,000 years ago by traveling across the area now known as the Bering Strait. FORMATION OF MOUNTAIN CHAINS Central Rocky Mountains Alps Himalayas 60 30 20 CORE ALLOSAURUS This carnivore measured 39 feet (12 m) long. MAMMOTHS Mammoths lived in Siberia. The cause of their extinction is still under debate. Carbon dioxide levels increase. Average temperatures are higher than today. The level of oxygen (O2) in the atmosphere is much lower than today. The global average temperature is at least 62° F (17° C). The ice layer covering Antarctica later thickens. Temperatures drop to levels similar to those of today. The lower temperatures cause forests to shrink and grasslands to expand. Vast development of feathered bird species and mammals covered with long fur THE AGE OF FLOWERING PLANTS At the end of the Cretaceous Period, the first angiosperms—plants with protected seeds, flowers, and fruits—appear. 10 DYNAMICS OF THE EARTH’S CRUST ANOTHER MASS EXTINCTION Toward the end of the Cretaceous Period, about 50 percent of existing species disappear. The dinosaurs, the large marine reptiles (such as the Plesiosaurs), the flying creatures of that period (such as the Pterosaurs), and the ammonites (cephalopod mollusks) disappear from the Earth. At the beginning of the Cenozoic Era, most of the habitats of these extinct species begin to be occupied by mammals. Outer Core The outer core is 1,400 miles (2,270 km) thick and contains melted iron, nickel, and other minor chemical compounds. Inner Core The inner core has a diameter of 756 miles (1,216 km). It is made of iron and nickel, which are solidified due to their exposure to high pressure and temperature conditions. Minerals, such as iron and silicates, are widely spread among the major constituents of the crust. Only the movements of the crust on the molten mantle disrupt their equilibrium. Elements in Equilibrium The diameter of the crater produced by the impact of the meteor on the Yucatán Peninsula. It is now buried under almost 2 miles (3 km) of limestone. 62 miles (100 km) CRUST The Earth's crust can reach a thickness of up to 6 miles (10 km) at the bottom of the ocean and up to 30 miles (50 km) on the continents. MANTLE The mantle is 1,800 miles (2,900 km) thick and is composed mainly of solid rock. Its temperature increases with depth. A notable component of the upper mantle is the asthenosphere, which is semisolid. In the asthenosphere, superficial rock layers that will eventually form the Earth's crust are melted. LITHOSPHERE The solid rock coating of the Earth, which includes the exterior of the mantle PlioceneOligocene ROCKS AND MINERALS 1312 DYNAMICS OF THE EARTH’S CRUST Under Construction O ur planet is not a dead body, complete and unchanging. It is an ever-changing system whose activity we experience all the time: volcanoes erupt, earthquakes occur, and new rocks emerge on the Earth's surface. All these phenomena, which originate in the interior of the planet, are studied in a branch of geology called internal geodynamics. This science analyzes processes, such as continental drift and isostatic movement, which originate with the movement of the crust and result in the raising and sinking of large areas. The movement of the Earth's crust also generates the conditions that form new rocks. This movement affects magmatism (the melting of materials that solidify to become igneous rocks) and metamorphism (the series of transformations occurring in solid materials that give rise to metamorphic rocks). Magmatism Magma is produced when the temperature in the mantle or crust reaches a level at which minerals with the lowest fusion point begin to melt. Because magma is less dense than the solid material surrounding it, it rises, and in so doing it cools and begins to crystallize. When this process occurs in the interior of the crust, plutonic or intrusive rocks, such as granite, are produced. If this process takes place on the outside, volcanic or effusive rocks, such as basalt, are formed. INNER CRUST Plutonic Rocks OUTER CRUST Volcanic rocks Metamorphism An increase in pressure and/or temperature causes rocks to become plastic and their minerals to become unstable. These rocks then chemically react with the substances surrounding them, creating different chemical combinations and thus causing new rocks to form. These rocks are called metamorphic rocks. Examples of this type of rock are marble, quartzite, and gneiss. Folding Although solid, the materials forming the Earth's crust are elastic. The powerful forces of the Earth place stress upon the materials and create folds in the rock. When this happens, the ground rises and sinks. When this activity occurs on a large scale, it can create mountain ranges or chains. This activity typically occurs in the subduction zones. Fracture When the forces acting upon rocks become too intense, the rocks lose their plasticity and break, creating two types of fractures: joints and faults. When this process happens too abruptly, earthquakes occur. Joints are fissures and cracks, whereas faults are fractures in which blocks are displaced parallel to a fracture plane. FOLDS For folds to form, rocks must be relatively plastic and be acted upon by a force. RUPTURE When rocks rupture quickly, an earthquake occurs. Oceanic Plate Magmatic Chamber Asthenosphere Crust Convective Currents PRESSURE This force gives rise to new metamorphic rocks, as older rocks fuse with the minerals that surround them. TEMPERATURE High temperatures make the rocks plastic and their minerals unstable. Zone of Subduction62 miles (100 km) Sea Level 124 miles (200 km) KILAUEA CRATER Hawaii Latitude 19° N Longitude 155° W ROCKS AND MINERALS 1514 DYNAMICS OF THE EARTH’S CRUST A Changing Surface T he molding of the Earth's crust is the product of two great destructive forces: weathering and erosion. Through the combination of these processes, rocks merge, disintegrate, and join again. Living organisms, especially plant roots and digging animals, cooperate with these geologic processes. Once the structure of the minerals that make up a rock is disrupted, the minerals disintegrate and fall to the mercy of the rain and wind, which erode them. Weathering Mechanical agents can disintegrate rocks, and chemical agents can decompose them. Disintegration and decomposition can result from the actions of plant roots, heat, cold, wind, and acid rain. The breaking down of rock is a slow but inexorable process. WATER In a liquid or frozen state, water penetrates into the rock fissures, causing them to expand and shatter. A variety of forces can cause rock fragments to break into smaller pieces, either by acting on the rocks directly or by transporting rock fragments that chip away at the rock surface. MECHANICAL PROCESSES Erosion External agents, such as water, wind, air, and living beings, either acting separately or together, wear down, and their loose fragments may be transported. This process is known as erosion. In dry regions, the wind transports grains of sand that strike and polish exposed rocks. On the coast, wave action slowly eats away at the rocks. In this process, materials eroded by the wind or water are carried away and deposited at lower elevations, and these new deposits can later turn into other rocks. EOLIAN PROCESSES The wind drags small particles against the rocks. This wears them down and produces new deposits of either loess or sand depending on the size of the particle. CORKSCREW CANYON Arizona Latitude 36° 30´ N Longitude 111° 24´ W CHEMICAL PROCESSES The mineral components of rocks are altered. They either become new minerals or are released in solution. TEMPERATURE When the temperature of the air changes significantly over a few hours, it causes rocks to expand and contract abruptly. The daily repetition of this phenomenon can cause rocks to rupture. Transportation and Sedimentation Cave Water current Limestone River HYDROLOGIC PROCESSES All types of moving water slowly wear down rock surfaces and carry loose particles away. The size of the particles that are carried away from the rock surface depends on the volume and speed of the flowing water. High-volume and high- velocity water can move larger particles. Wind 112 elements listed in the periodic table. MINERALS COME FROM Components The basic components of minerals are the chemical elements listed on the periodic table. Minerals are classified as native if they are found in isolation, contain only one element, and occur in their purest state. On the other hand, they are classified as compound if they are composed of two or more elements. Most minerals fall into the compound category. NATIVE MINERALS These minerals are classified into: GOLD An excellent thermal and electrical conductor. Acids have little or no effect on it. A- METALS AND INTERMETALS Native minerals have high thermal and electrical conductivity, a typically metallic luster, low hardness, ductility, and malleability. They are easy to identify and include gold, copper, and lead. B- SEMIMETALS Native minerals that are more fragile than metals and have a lower conductivity. Examples are arsenic, antimony, and bismuth. C- NONMETALS An important group of minerals, which includes sulfur Isotypic Minerals Isomorphism happens when minerals with the same structure, such as halite and galena, exchange cations. The structure remains the same, but the resulting substance is different, because one ion has been exchanged for another. An example of this process is siderite (rhombic FeCO3), which gradually changes to magnesite (MgCO3) when it trades its iron (Fe) for similarly- sized magnesium (Mg). Because the ions are the same size, the structure remains unchanged. Polymorphism A phenomenon in which the same chemical composition can create multiple structures and, consequently, result in the creation of several different minerals. The transition of one polymorphous variant into another, facilitated by temperature or pressure conditions, can be fast or slow and either reversible or irreversible. types of minerals have been recognized by the International Association of Mineralogy. MORE THAN Chemical Composition CaCO3 CaCO3 FeS2 FeS2 C C Crystallization System Mineral Calcite Aragonite Pyrite Marcasite Diamond Graphite DIAMOND AND GRAPHITE A mineral's internal structure influences its hardness. Both graphite and diamond are composed only of carbon; however, they have different degrees of hardness. Atoms form hexagons that are strongly interconnected in parallel sheets. This structure allows the sheets to slide over one another. Each atom is joined to four other atoms of the same type. The carbon network extends in three dimensions by means of strong covalent bonds. This provides the mineral with an almost unbreakable hardness. Diamond Graphite Trigonal Rhombic Cubic Rhombic Cubic Hexagonal Model demonstrating how one atom bonds to the other four Hardness of 10 on the Mohs scale Halite NaCl Galena PbS Cl Na S Pb HALITE AND GALENA Hardness of 1 on the Mohs scale Cubic Internal Structure Carbon Atom SILVER The close-up image shows the dendrites formed by the stacking of octahedrons, sometimes in an elongated form. Microphotograph of silver crystal dendrites SULFURBISMUTH HALITE is composed of chlorine and sodium. 1 2 COMPOUND MINERALS Compound minerals are created when chemical bonds form between atoms of more than one element. The properties of a compound mineral differ from those of its constituent elements. M inerals are the “bricks” of materials that make up the Earth and all other solid bodies in the universe. They are usually defined both by their chemical composition and by their orderly internal structure. Most are solid crystalline substances. However, some minerals have a disordered internal structure and are simply amorphous solids similar to glass. Studying minerals helps us to understand the origin of the Earth. Minerals are classified according to their composition and internal structure, as well as by the properties of hardness, weight, color, luster, and transparency. Although more than 4,000 minerals have been discovered, only about 30 are common on the Earth's surface. You Are What You Have 20 MINERALS ROCKS AND MINERALS 21 4,000 22 MINERALS A Question of Style O ptical properties involve a mineral's response to the presence of light. This characteristic can be analyzed under a petrographic microscope, which differs from ordinary microscopes in that it has two devices that polarize light. This feature makes it possible to determine some of the optical responses of the mineral. However, the most precise way to identify a mineral by its optical properties is to use an X-ray diffractometer. EXOTIC COLOR QUARTZ ROCK CRYSTAL Colorless; the purest state of quartz SMOKY Dark, brown, or gray minerals CITRINE The presence of iron produces a very pale yellow color. AMETHYST The presence of iron in a ferric state results in a purple color. ROSE The presence of manganese results in a pink color. Refraction and Luster Refraction is related to the speed with which light moves through a crystal. Depending on how light propagates through them, minerals can be classified as monorefringent or birefringent. Luster results from reflection and refraction of light on the surface of a mineral. In general, it depends on the index of refraction of a mineral's surface, the absorption of incident light, and other factors, such as concrete characteristics of the observed surface (for instance, degree of smoothness and polish). Based on their luster, minerals can be divided into three categories. METALLIC Minerals in this class are completely opaque, a characteristic typical of native elements, such as copper, and sulfides, such as galena. SUBMETALLIC Minerals in this class have a luster that is neither metallic nor nonmetallic. NONMETALLIC Minerals in this class transmit light when cut into very thin sheets. They can have several types of luster: vitreous (quartz), pearlescent, silky (talc), resinous, or earthy. Color is one of the most striking properties of minerals. However, in determining the identity of a mineral, color is not always useful. Some minerals never change color; they are called idiochromatic. Others whose colors are variable are called allochromatic. A mineral's color changes can be related, among other things, to the presence of impurities or inclusions (solid bodies) inside of it. Streak is the color of a mineral's fine powder, which can be used to identify it. Some minerals always have the same color; one example is malachite. INHERENT COLOR A mineral can have several shades, depending on its impurities or inclusions. Luminescence Certain minerals emit light when they are exposed to particular sources of energy. A mineral is fluorescent if it lights up when exposed to ultraviolet rays or X-rays. It is phosphorescent if it keeps glowing after the energy source is removed. Some minerals will also respond to cathode rays, ordinary light, heat, or other electric currents. MALACHITE SULFUR Other secondary minerals, known as exotic minerals, are responsible for giving quartz its color; when it lacks exotic minerals, quartz is colorless. AGATE A type of chalcedony, a cryptocrystalline variety of quartz, of nonuniform coloring More reliable than a mineral's color is its streak (the color of the fine powder left when the mineral is rubbed across a hard white surface). COLOR STREAK Agates crystallize in banded patterns because of the environments in which they form. They fill the cavities of rocks by precipitating out of aqueous solutions at low temperatures. Their colors reflect the porosity of the stone, its degree of inclusions, and the crystallization process. HEMATITE Color: Black Streak Color: Reddish Brown ROCKS AND MINERALS 23 ROCKS AND MINERALS 2524 MINERALS How to Recognize Minerals A mineral's physical properties are very important for recognizing it at first glance. One physical property is hardness. One mineral is harder than another when the former can scratch the latter. A mineral's degree of hardness is based on a scale, ranging from 1 to 10, that was created by German mineralogist Friedrich Mohs. Another physical property of a mineral is its tenacity, or cohesion—that is, its degree of resistance to rupture, deformation, or crushing. Yet another is magnetism, the ability of a mineral to be attracted by a magnet. Exfoliation and Fracture When a mineral tends to break along the planes of weak bonds in its crystalline structure, it separates into flat sheets parallel to its surface. This is called exfoliation. Minerals that do not exfoliate when they break are said to exhibit fracture, which typically occurs in irregular patterns. 1. TALC is the softestmineral. 2. GYPSUMcan be scratchedby a fingernail. 3. CALCITE is as hard as abronze coin. 4. FLUORITE can be scratchedby a knife. 5. APATITE can be scratchedby a piece of glass. 6. ORTHOCLASE can be scratchedby a drill bit. 7. QUARTZ can be scratchedby tempered steel. 8. TOPAZcan be scratchedwith a steel file. 9. CORUNDUM can be scratchedonly by diamond. 10. DIAMONDis the hardestmineral. TYPES OF EXFOLIATION Cubic Octahedral Dodecahedral Rhombohedral Prismatic and Pinacoidal Pinacoidal (Basal) ranks 10 minerals, from the softest to the hardest. Each mineral can be scratched by the one that ranks above it. MOHS SCALE FRACTURE can be irregular, conchoidal, smooth, splintery, or earthy. 7 to 7.5 IS THE HARDNESS OF THE TOURMALINE ON THE MOHS SCALE. Electricity Generation Piezoelectricity and pyroelectricity are phenomena exhibited by certain crystals, such as quartz, which acquire a polarized charge because exposure to temperature change or mechanical tension creates a difference in electrical potential at their ends. PIEZOELECTRICITY The generation of electric currents that can occur when mechanical tension redistributes the negative and positive charges in a crystal. Tourmaline is an example. PYROELECTRICITY The generation of electric currents that can occur when a crystal is subjected to changes in temperature and, consequently, changes in volume. PRESSURE Positive charge Negative charge Positive charge Negative charge HEAT IRREGULAR FRACTURE An uneven, splintery mineral surface TOURMALINE is a mineral of the silicate group. COLOR Some tourmaline crystals can have two or more colors. DENSITY reflects the structure and chemical composition of a mineral. Gold and platinum are among the most dense minerals. ROCKS AND MINERALS 3130 MINERALS Crystalline Symmetry T here are more than 4,000 minerals on Earth. They appear in nature in two ways: without an identifiable form or with a definite arrangement of atoms. The external expressions of these arrangements are called crystals, of which there are 32 classes. Crystals are characterized by their organized atomic structure, called a crystalline network, built from a fundamental unit (unit cell). These networks can be categorized into the seven crystalline systems according to the crystal's arrangement. They can also be organized into 14 three-dimensional networks, known as the Bravais lattices. Typical Characteristics A crystal is a homogeneous solid whose chemical elements exhibit an organized internal structure. A unit cell refers to the distribution of atoms or molecules whose repetition in three dimensions makes up the crystalline structure. The existence of elements with shared symmetry allows the 32 crystal classes to be categorized into seven groups. These groups are based on pure geometric shapes, such as cubes, prisms, and pyramids. Bravais Lattices In 1850, Auguste Bravais demonstrated theoretically that atoms can be organized into only 14 types of three-dimensional networks. These network types are therefore named after him. Cubic Three crystallographic axes meet at 90° angles. Hexagonal prisms have six sides, with 120º angles. From one end, the cross section is hexagonal. Monoclinic Prisms look like tetragonal crystals cut at an angle. Their axes do not meet at 90º angles. Tetragonal These crystals are shaped like cubes, but one of their facets is longer than the others. All three axes meet at 90º angles, but one axis is longer than the other two. Triclinic These crystals have very odd shapes. They are not symmetrical from one end to the other. None of their three axes meet at 90º angles. Trigonal This system includes the most characteristic rhombohedrons, as well as hexagonal prisms and pyramids. Three equal axes meet at 120º, with one axis meeting at 90º to the center. Rhombic Three nonequivalent crystallographic axes meet at 90º angles. THE MOST COMMON SHAPES Cube Octahedron Rhombo- dodecahedron Tetrahedron Hexagonal Prism Hexagonal Bipyramid Hexagonal Prism Combined with Hexagonal Bipyramid Simple Cubic Network Body-centered Cubic Network Face-centered Cubic Network Prisms Combined with Pinacoids Prism Hexagonal Prism Combined with Basal Pinacoid Simple Monoclinic Network Monoclinic Network Centered on its Bases Only 14 network combinations are possible. THESE COMBINATIONS ARE CALLED BRAVAIS LATTICES. Tetragonal Prism and Ditetragonal Prism Tetragonal Bipyramid Prism and Bipyramid Simple Tetragonal Centered Tetragonal Triclinic Shapes Triclinic Network Triclinic Network Simple Rhombus Base- centered Rhombus Centered Rhombus Face- centered Rhombus Pinacoids Prism and Basal Pinacoid Bipyramid Prism and Domes Prisms, Domes, and Two Pinacoids Trigonal or Rhombohedral Shapes Trigonal Trapezohedron Ditrigonal Scalenohedron A crystal's ideal plane of symmetry passes through its center and divides it into two equal, symmetrical parts. Its three crystallographic axes pass through its center. A crystal's longest vertical axis is called “c,” its transverse axis “b,” and its shortest (from front to back) “a.” The angle between c and b is called alpha; the one between a and c, beta; and the one between a and b, gamma. CRYSTAL SYMMETRY Vertical Axis Horizontal Plane Sagittal Plane Frontal Plane Anteroposterior Axis Transverse Axis There are seven crystalline systems. The 32 existing crystal classes are grouped into these crystalline systems. LEGEND CRYSTALLINE SYSTEM BRAVAIS LATTICES CRYSTALLOGRAPHIC OR COORDINATE AXES Vanadinite Brazilianite Diamond Scheelite Labradorite Rhodochrosite TopazTRICLINIC 7% RHOMBIC 22% CUBIC 12% TETRAGONAL 12% TRIGONAL 9% HEXAGONAL 8% HOW MINERALS CRYSTALLIZE MONOCLINIC 32% Precious Crystals P recious stones are characterized by their beauty, color, transparency, and rarity. Examples arediamonds, emeralds, rubies, and sapphires. Compared to other gems, semiprecious stones arecomposed of minerals of lesser value. Today diamonds are the most prized gem for their “fire,” luster, and extreme hardness. The origin of diamonds goes back millions of years, but people began to cut them only in the 14th century. Most diamond deposits are located in South Africa, Namibia, and Australia. Diamond Mineral composed of crystallized carbon in a cubic system. The beauty of its glow is due to a very high refraction index and the great dispersion of light in its interior, which creates an array of colors. It is the hardest of all minerals, and it originates underground at great depths. EXTRACTION Diamonds are obtained from kimberlite pipes left over from old volcanic eruptions, which brought the diamonds up from great depths. CUTTING AND CARVING The diamond will be cut by another diamond to reach final perfection. This task is carried out by expert cutters. 2 3 1 B CUTTING: Using a fine steel blade, the diamond is hit with a sharp blow to split it. A INSPECTION:Exfoliation is determined in order to cut the diamond. C CARVING: With achisel, hammer, and circular saws, the diamond is shaped. POLISHING The shaping of the facets of the finished gem BRILLIANCE The internal faces of the diamond act as mirrors because they are cut at exact angles and proportions. FIRE Flashes of color from a well- cut diamond. Each ray of light is refracted into the colors of the rainbow. COMMON CUTS A diamond can have many shapes, as long as its facets are carefully calculated to maximize its brilliance. Gems Mineral, rock, or petrified material that, after being cut and polished, is used in making jewelry. The cut and number of pieces that can be obtained is determined based on the particular mineral and its crystalline structure. PRECIOUS STONES SEMIPRECIOUS STONES DIAMOND The presence of any color is due to chemical impurities. EMERALD Chromium gives it its characteristic green color. OPAL This amorphous silica substance has many colors. RUBY Its red color comes from chromium. SAPPHIRE Blue to colorless corundum. They can also be yellow. AMETHYST Quartz whose color is determined by manganese and iron TOPAZ A gem of variable color, composed of silicon, aluminum, and fluorine GARNET A mix of iron, aluminum, magnesium, and vanadium TURQUOISE Aluminum phosphate and greenish blue copper THE CHEMISTRY OF DIAMONDS Strongly bonded carbon atoms crystallize in a cubic structure. Impurities or structural flaws can cause diamonds to show a hint of various colors, such as yellow, pink, green, and bluish white. BRILLIANT EMERALD PRINCESS TRILLION PEAR HEART OVAL MARQUISE CROWN13.53 34.3° 40.9° 1.9 43.3 BEZEL STAR TABLE GIRDLE PAVILLION IDEAL DIAMOND STRUCTURE 100 55.1 M O U T H M A IN C O N D U IT R O O T RING OF WASTE MATERIAL ERODED LAVA KIMBERLEY MINE COOLED LAVA XENOLITHS PRESSURE ZONE 0 0.3 mi (0.5 km) 0.6 mi (1.0 km) 0.9 mi (1.5 km) 1.2 mi (2.0 km) 1.5 mi (2.5 km) miles (km) enters the diamond. The facets of the pavilion reflect the light among themselves. The light is reflected back to the crown in the opposite direction. The rays divide into their components. Each color reflects separately in the crown. LIGHT LIGHT 0.5 inch (13 mm) 0.3 inch (6.5 mm) 0.08 inch (2 mm) 8 CARATS 6.5 CARATS 0.03 CARAT 27.6 tons (25 metric tons) 1 carat = 0.007 ounce (0.2 grams) of mineral must be removed to obtain a 1 carat diamond. 320 microns(0.32 mm) MEASURED VERTICALLY ROCKS AND MINERALS 3332 MINERALS ROCKS AND MINERALS 3534 MINERALS Diamonds in History ORIGINAL CUT It formerly weighed 186 carats with 30 facets that merged into six facets, which, in turn, became one. This explains its name: Mountain of Light. The Great Koh-i-noor Diamond This diamond, which originated in India, now belongs to the British royal family. The raja of Malwa owned it for two centuries, until 1304, when it was stolen by the Mongols. In 1739 the Persians took possession of it. It witnessed bloody battles until finding its way back to India in 1813, after which point it reached the queen. Coronation of the Queen Mother The Queen Mother's Crown History ONLY FOR WOMEN Because this diamond was believed to bring unhappiness to men, the superstitious Queen Victoria added a clause to her will stating that the diamond should only be handed down to the wives of future kings. 9 LARGE AND 96 SMALL PIECES Joseph Asscher studied the huge stone for six months to decide how to cut it; he then divided it into nine primary stones and 96 smaller diamonds. In 1856 this diamond was offered to Queen Victoria as compensation for the Sikh wars. She then had it recut. The Koh-i-noor was diminished to 109 carats. 530 carats is the weight of the Cullinan I, the largest stone obtained from the original Cullinan find. It is followed by Cullinan II, which weighs 317 carats and is set in the imperial crown. Evalyn Walsh McLean 1669 Louis XIV acquires the gem. Hedied in agony of gangrene. 1830 Henry Hope buys the diamondand suffers under the curse; he soon sells it. 1918 While the stone is in the handsof members of the McLean family, the patriarch and two of his daughters die. ORIGINAL CUT The purest of blue from the presence of boronic impurities, the diamond's color is also influenced by the presence of nitrogen, which adds a pale yellow shade. FINAL CUT THE GREAT STAR OF AFRICA This gem is the second largest cut diamond in the world, weighing 530 carats. Because it belongs to the British Crown, it is on display in the Tower of London. 13.53 43.3 100 THE TAYLOR-BURTON DIAMOND This diamond, with a weight of 69.42 carats, was auctioned in 1969. The day after buying it, Cartier sold it to the actor Richard Burton for $1.1 million. His wife Elizabeth Taylor tripled its value when she sold it after divorcing him. THE LEGEND OF THE VALLEY OF DIAMONDS Alexander the Great introduced the legend of the Valley of Diamonds to Europe. According to this ancient account, later incorporated into the book The Thousand and One Nights, there was an inaccessible valley located in the mountains of northern India. The bed of this valley was covered with diamonds. To obtain them, raw meat was thrown in the valley and then fetched by trained birds, which would return it encrusted with diamonds. Elizabeth Taylor FINAL CUT D iamonds are a sign of status, and their monetary value is determined by the law of supply and demand. First discovered by Hindus in 500 BC, diamonds gained fame in the early 20th century when they were advertised in the United States as the traditional gift from husbands to their wives. Some diamonds became famous, however, not only for their economic value but also for the tales and myths surrounding them. The Misfortune of Possessing Hope The Hope Diamond is legendary for the harm it brought to its owners since being stolen from the temple of the goddess Sita in India. According to the legend, its curse took lives and devoured fortunes. In 1949 diamond expert Harry Winston bought it and in 1958 donated it to the Smithsonian Institution, in Washington, D.C., where it can be viewed by the public. Legend Over the years, belief in the curse of the Hope Diamond was reinforced as its owners fell into ruin. Evalyn Walsh McLean, the last private owner of the diamond, did not sell it even after several tragedies befell her family. Cullinan, the Greatest Find Discovered in 1905 in South Africa, this diamond is the biggest ever found. It was sold to the government of Transvaal two years after its discovery for $300,000 (£150,000). It was then given to Edward VII on the occasion of his 66th birthday. The king entrusted the cutting of the diamond to Joseph Asscher of The Netherlands, who divided it into 105 pieces. IF STONES COULD SPEAK 52-53 METAMORPHIC PROCESSES 54-55 THE BASIS OF LIFE 56-57 DIVINE AND WORSHIPED 58-59 Formation and Transformation of Rocks N atural forces create an incredible variety of landscapes, such as deserts, beaches, elevated peaks, ravines, canyons, and underground caves. Settings like the one in the picture amaze us and arouse our interest in finding out what is hidden in the cave's depths. Rocks subjected to high pressure and temperatures can undergo remarkable changes. An initially igneous rock can become sedimentary and later metamorphic. There are experts who overcome every type of obstacle to reach inhospitable places, even in the bowels of the Earth, in search of strange or precious materials, such as gold and silver. They also look for fossils to learn about life- forms and environments of the past. ROCKS OF FIRE 42-43 SCULPTED VALLEY 44-45 EVERYTHING CHANGES 46-49 DARK AND DEEP 50-51 SUBTERRANEAN WORLD This awe-inspiring limestone cave in Neversink Pit (Alabama) looks like no other place on Earth. 42 FORMATION AND TRANSFORMATION OF ROCKS Rocks of Fire ROCKS AND MINERALS 43 I gneous (from Latin ignis, “fire”) rocks form when magma coming from the rocky mantle (underneath the crust) rises, cools, and solidifies. When magma comes to the surface as lava and solidifies relatively quickly, it creates extrusive rocks, such as basalt or rhyolite. On the other hand, when magma seeps into caves or between rock layers and slowly solidifies, intrusive igneous rocks, such as gabbro and granite, are formed. These rocks usually have thicker grains and are less dense than the extrusive ones. They are arranged in structures called dikes, sills, and batholiths beneath the surface. Igneous rocks make up most of the Earth's crust. ASH CONE Composed of pyroclasts of the volcano itself LACCOLITH is located between superficial layers. CALDERA Collapsed volcanic crater covered with water A Complex Process The Earth's crust is 44 miles (70 km) deep at most. Farther down, rocks are molten or semimolten, forming magma that rises through the crust and opens paths through cracks, cavities, or volcanoes. Magma can solidify when it is moving or still or when underground or expelled to the surface. All these characteristics together with different mineral compositions create a wide variety of igneous rocks. SOLID ROCK MUD FLATS LAKE VOLCANIC OUTCROPPING BRANCHING LACCOLITH ERODED LAVA FLOW BENEATH THE SURFACE PLUTONIC ROCKS Most magma is underground in the form of plutons, which undergo a solidification process. This forms intrusive (or plutonic) rocks. When magma intrudes into vertical fissures, the resulting rock formations are called dikes; those between sedimentary layers are sills; and batholiths are masses hundreds of miles long. In general, intrusive rocks crystallize slowly, and their minerals form thick grains. But the solidification process will determine the structure; the rock will be different depending on whether solidification is slow (over millions of years) or fast and whether it loses or gains materials along the way. ROCKY MANTLE 1,800 miles (2,900 km) thick CORE The outer core is made of solid iron and melted nickel. CRUST Rigid, outermost layer LATERAL VENTS MAIN VENT PYROCLASTS Rock fragments and ash that spread out over miles SILLS occupy the spaces between overlying layers of rocks. MAGMA CHAMBER receives magma material from the mantle. MAGMA TEMPERATURE AT A DEPTH OF 125 MILES (200 KM) 2,550º F (1,400º C) THE TEMPERATURE OF LAVA IN THE CRUST 2,200º F (1,200º C) GRANITE Composed of feldspar and quartz crystals, it is rich in sodium, potassium, and silica. SILICA CONTENT70% SILICA CONTENT According to the type of lava 50%BASALT ROCKoriginates from highly liquid fluid magma that cools quickly. SURROUNDING ROCK INTRUSIVE ROCK MAGMA RISES because of the melted rock's low density. BATHOLITH can be an old magma chamber that has solidified over thousands of years. AGATE ROCK M A G M A LAVA PLATEAU Composed of rhyolitic volcanic lava (rich in silicon) DIKE Formed by magma that intruded into a vertical fracture Bowen's Reaction Series Different magma materials solidify at different temperatures. Minerals with calcium, iron, and magnesium crystallize first, giving them a dark coloring (olivine, pyroxene). But sodium, potassium, and aluminum crystallize at lower temperatures, remaining in the residual magma until the end of the process. They are present only in pale-colored rock, which crystallizes later. Sometimes different stages of the process can be seen in the same rock. LAST LAYER TO CRYSTALLIZE COOLING OF MAGMA FIRST LAYER TO CRYSTALLIZE RICH IN SODIUM RICH IN CALCIUM ON THE SURFACE VOLCANIC ROCK Volcanic, or extrusive, rocks are those that reach the surface as lava because of volcanic activity. They solidify relatively quickly on the surface. Some, like the obsidians, solidify too quickly to crystallize. This class of rock is distinguished by its viscosity, caused by the low silica content and dissolved gas at the moment of eruption, which give these rocks a particular texture. Highly liquid lava, such as basalt, usually covers large surfaces because it solidifies on the outside while still remaining fluid underground. STOCKS are massive plutons smaller than batholiths.DIKES The structure of the rock depends on its formation process. Thus, a rock resulting from magma intrusion into a dike will have a structure and coloring different from the rock around it because of having crystallized faster. 44 FORMATION AND TRANSFORMATION OF ROCKS ROCKS AND MINERALS 45 Y osemite National Park is located 200 miles (320 km) east of San Francisco, California. This park is known worldwide for its granite cliffs, waterfalls, crystalline rivers, and forests of giant sequoias. It covers an area of 1,190 square miles (3,081 sq km) and extends along the eastern slopes of the Sierra Nevada range. Yosemite National Park has over three million visitors every year. Sculpted Valley HALF DOME Granite monolith of unique beauty. It is lower than El Capitan, being 2,160 feet (660 m) high. 87 Million Years Ago YOSEMITE NATIONAL PARK United States Latitude 37° N Longitude 119° W Location Surface Visitors in 2005 Opened on Administered by California 1,190 square miles (3,081 sq km) 3,380,038 9/25/1890 National Park Service CASCADES Some rock formations in the park serve as platforms for waterfalls, especially in April, May, and June when the snow melts upstream. The valley has nine waterfalls, five of which are over 1,000 feet (300 m) high; Yosemite Falls is 2,600 feet (800 m) high. This is the highest waterfall in North America and the third highest in the world. Yosemite This park has an average elevation of 1,300 to 2,000 feet (400-600 m) above sea level. The geology of the area is mostly composed of a granitic batholith, but five percent of the park is composed of formations from the metamorphism of volcanic and sedimentary rocks. Erosion at different elevations and fracture systems created valleys, canyons, hills, and other current geological formations. The wide separation between fractures and joints is caused by the amount of silica present in the granite and in the metamorphic rocks. EL CAPITAN 300-foot-high (1,000 m) granite cliff used for mountain climbing FOREST The park has three groves of giant sequoias, among other species. 103 Million Years BRIDAL VEIL FALLS This huge waterfall formed as a consequence of glacial thaw in a “hanging” valley. 616 feet (188 m) FREE FALL CATHEDRAL ROCKS One of the main rock formations, with compacted and scratched granite walls 103 Million Years Ago FISSURES The erosion at rock joints causes fissures within them, and this process leads to the formation of valleys and canyons. The downward flow of the glacial mass of ice cut and sculpted the valley into a U shape. Today this unique landscape attracts great numbers of visitors. FORMATION OF THE LANDSCAPE Erosion in the joints resulted in valleys and canyons. The strongest erosive forces of the last several million years have been glaciers, which changed the V-shaped valleys created by rivers into U-shaped glacial valleys. BATHOLITH FORMATION Almost all rocky formations at Yosemite Park are composed of granite; they belong to the original batholith. 1 ASCENTTen million years ago, the Sierra Nevada underwent a tectonic elevation that caused the batholith to emerge. 2 EROSION One million years ago, the descending flow of glacial ice gave the valley a U shape. 3 GLACIATION ROCK Compact granite forming a large batholith FISSURE Produced by erosion at rock joints GRANITE ELEVATION V-SHAPED SLOPES U-SHAPED CANYONS 50 FORMATION AND TRANSFORMATION OF ROCKS A cave is a hollow space created essentially through the chemical action of water on a soluble, usually chalky, material. Caves have three structures: stalactites (conical structures that hang from the cave ceiling), stalagmites (structures that jut from the cave floor), and columns (created when stalactites and stalagmites join). The cycle of cave formation is called the karst cycle, which lasts a total of around one million years. For this reason, young, active caves have noisy streams and cascades, whereas old caves are silent wonders decorated with stalagmites, stalactites, and columns. Dark and Deep ROCKS AND MINERALS 51 CANGO CAVES SOUTH AFRICA Latitude 33º S Longitude 18º E Length Depth Location 3.3 miles (5.3 km) 200 feet (60 m) East of Cape Town When water dissolves high calcium content rock through the corrosive effect of carbonic acid, it forms networks of conduits and galleries. The initial fissures widen not only through this chemical process but also mechanically through the abrasive action of pebbles and other insoluble elements. Water is filtered until it reaches lower levels, leaving in its wake openings arranged in levels and separated by vertical pits and passages that connect the different levels. The Karst Cycle Stalactite Formation Limestone is a rock composed almost exclusively of calcium carbonate, which dissolves in naturally acid water. Rainwater absorbs carbon dioxide from the air and microorganisms from the ground, becoming a weak acid. When filtered, it can dissolve limestone over time. If this water drips into a cave, it loses carbon dioxide to the air and deposits the excess calcium in stalactites and stalagmites, thereby maintaining chemical equilibrium. Stalactites are excellent examples of chemical sedimentary rocks. COLUMN If stalactites and stalagmites grow until they join together, they become columns. 130 feet (39 m) THE HIGHEST COLUMN IN THE WORLD 65º F (18º C) IDEAL TEMPERATURE FOR THE PRECIPITATION OF CARBONATE 100 feet (30 m) THE TALLEST STALAGMITE IN THE WORLD 23 feet (7 m) THE BIGGEST STALACTITE IN THE WORLD STRUCTURE OF THE STRATUM OF A CAVE The ground's original structure is composed of permeable limestone. It has fissures through which river or rainwater is filtered. This starts the erosive process. 1 INITIAL CAVE Water, following the contour of the terrain, forms an underground river. The first calcite or calcium carbonate deposits start to form in the shape of stalactites. 2 EXTENDED CAVE SYSTEM Formed when several tunnels are joined together. Sometimes the surface of the soil starts to sink, creating sinkholes. If the cave extends below the water table, tunnels are formed. 3 FLAT GROUND TUNNEL DRY GALLERY TUNNEL VAULT CALCITE DEPOSITS WATER FILTRATION UNDERGROUND SEQUENCE PERMEABLE LIMESTONE CAVERN FISSURE IMPERMEABLE ROCK SINKHOLE CANGO CAVES Isolated in a narrow strip of limestone from the Precambrian, in the highlands of Oudtshoorn, the Cango Caves are remarkable for their abundant deposits of calcite. They are left over from a larger channel below the water table. This channel dried up when the neighboring surface valleys were worn down to lower levels. The impressive stalagmites were then formed.. STALACTITES can form on ceilings and cement floors, although they form much faster in a cave's natural environment that contains carbon-rich solutions. MORE LAYERS Each successive droplet that falls deposits another fine calcite layer. 3 INTERIOR TUBE The layers form around a narrow pipe (0.02 inch [0.5 mm]) through which the water seeps. 4 STALACTITE If many droplets are deposited over this pipe, stalactites are formed. 5 WATER DROPLET Every stalactite starts from a simple water droplet containing dissolved salts. 1 CALCITE When the droplet falls, it leaves behind a narrow calcite trail. 2 Water Droplet Other Formations A passing underground current forms two types of landscape: canyons and tunnels. Underground rivers and waterfalls above the water table create deep, undulating canyons by eroding and dissolving limestone and by abrading the rock layers with sediment. Below the water table, caves are full of water that moves slowly, dissolving walls, floors, and ceilings of carbonate rock to create tunnels. STALAGMITE Water droplets containing dissolved carbonate create stalagmites as they drip down. 52 FORMATION AND TRANSFORMATION OF ROCKS If Stones Could Speak R ock strata form from sediments deposited over time in successive layers. Sometimes these sediments bury remains of organisms that can later become fossils, which provide key data about the environment and prehistoric life on Earth. The geologic age of rocks and the processes they have undergone can be discovered through different methods that combine analyses of successive layers and the fossils they contain. Fossils succeeded one another in a definite order, which makes it possible to date past events. The existence of identical fossils on different continents helps establish correlations and assigns the same age to widely separated geographic areas. PRINCIPLE OF SUCCESSION Rock Layers and the Passage of Time Rock layers are essential for time measurement because they retain information not only about the geologic past but also about past life-forms, climate, and more. The principle of original horizontality establishes that the layers of sediment are deposited horizontally and parallel to the surface and that they are defined by two planes that show lateral continuity. If layers are folded or bent, they must have been altered by some geologic process. These ruptures are called unconformities. If the continuity between layers is interrupted, it means that there was an interval of time and, consequently, erosion in the layer below. This also is called unconformity, since it interrupts the horizontality principle. A Fossil's Age Fossils are remains of organisms that lived in the past. Today scientists use several procedures, including carbon-14 dating, to estimate their age. This method makes it possible to date organic remains with precision from as long ago as 60,000 years. If organisms are older, there are other methods for absolute dating. However, within a known area, a fossil's location in a given sedimentary layer enables scientists to place it on an efficient, relative time scale. Following principles of original horizontality and of succession, it is possible to find out when an organism lived. When it dies, an animal can be submerged on a riverbed, protected from oxygen. The body begins to decompose. 1. The skeleton is completely covered with sediments. Over the years, new layers are added, burying the earlier layers. During fossilization, molecules of the original tissue are replaced precisely with minerals that petrify it. 2. Once the water disappears, the fossil is already formed and crystallized. The crust's movements raise the layers, bringing the fossil to the surface. 3. ROCKS AND MINERALS 53 TRILOBITES are extinct arthropods. They were solitary marine creatures, and they had a segmented body and an exoskeleton of the protein chitin, with pairs of jointed limbs. Together with graptolites they are one of the most characteristic fossils from Paleozoic marine sediments. Unconformity Angular Unconformity Colorado River Disconfo rmity Parac onfor mity COCONINO PLATFORM TONTO PLATFORM TONTO PLATFORM Zoroaster Granite VISHNU SCHISTS Muav Limestone PRECAMBRIAN CAMBRIAN DEVONIAN CARBONIFEROUS PERMIAN Unconformity between the Tonto Group and the Redwall Limestone indicates a temporal hiatus. Between the Redwall Limestone and the Supai Group, there is temporal continuity. TEMPORAL HIATUS Period Hermit Shale 460 feet (140 m) 1,000 feet (310 m) UNKAR GROUP REDWALL LIMESTONE TONTO GROUP SUPAI GROUP Erosion exposes the fossil to full view. With carbon-14 dating, scientists can determine if it is less than 60,000 years old. 4. Cononino Sandstone The Grand Canyon tells the history of the Earth in colorful layers on its walls. The Colorado River has been carving its way through the plateau for six million years. The layers along the river provide an uninterrupted account of geological history. CONTINUITY Bright Angel Shale GONDWANA PALEOSIBERIA EUROAMERICA GRAND CANYON Colorado River Arizona Latitude 36° N Length 112° W ROCKS AND MINERALS 5554 FORMATION AND TRANSFORMATION OF ROCKS As the pressure increases on the rocks, the mineralogical structure of rocks is reorganized, which reduces their size. PRESSURE Intermediate Crust 1 2 Slate In environments with high temperature and pressure, slates will become phyllites. Schist Lower Crust The closer the rock is to the heat source and the greater the temperature, the higher the degree of metamorphism that takes place. TEMPERATURE 1 2 Magma Sandstone Magma Schist Limestone Quarzite Hornfels Marble Scotland was raised in the Caledonian orogeny 400 million years ago. This pressure produced the gneiss shown in the photo. SCOTLAND, United Kingdom Latitude 57° N Longitude 04° W Regional Metamorphism As mountains form, a large amount of rock is deformed and transformed. Rocks buried close to the surface descend to greater depths and are modified by higher temperatures and pressures. This metamorphism covers thousands of square miles and is classified according to the temperature and pressure reached. Slate is an example of rock affected by this type of process. Contact Metamorphism Magmatic rocks transmit heat, so a body of magma can heat rocks on contact. The affected area, located around an igneous intrusion or lava flow, is called an aureole. Its size depends on the intrusion and on the magma's temperature. The minerals of the surrounding rock turn into other minerals, and the rock metamorphoses. Dynamic Metamorphism The least common type of metamorphism, dynamic metamorphism happens when the large-scale movement of the crust along fault systems causes the rocks to be compressed. Great rock masses thrust over others. Where they come in contact new metamorphic rocks, called cataclasites and mylonites, are formed. Metamorphic Processes W hen rocks are subjected to certain conditions (high pressure and temperature or exposure to fluids with dissolved chemicals), they can undergo remarkable changes in both their mineral composition and their structure. This very slow process, called metamorphism, is a veritable transformation of the rock. This phenomenon originates inside the Earth's crust as well as on the surface. The type of metamorphism depends on the nature of the energy that triggers the change. This energy can be heat or pressure. FUSION At this temperature, most rocks start to melt until they become liquid. 1,470° F (800° C) SCHIST Very flaky rock produced by metamorphism at intermediate temperatures and depths greater than six miles (10 km). The minerals recrystallize. 930° F (500° C)SLATEMetamorphic rock of low grade that forms through pressure at about 390° F (200° C). It becomes more compact and dense. 570° F (300° C) GNEISS Produced through highly metamorphic processes more than 12 miles (20 km) beneath the surface, it involves extremely powerful tectonic forces and temperatures near the melting point of rock. 1,200° F (650° C) ORGANIC ROCKS 70-71 COMMON METAMORPHIC ROCKS 72-73 INCREDIBLE PETRA 74-75 Classes of Rocks D ifferent types of rocks can be distinguished based on their luster, density, and hardness, among other properties. A geode looks like a common rock on the outside, but when it is cut in half, a fantastic range of colors and shapes can be revealed. The several classes of rocks can also be grouped according to how they formed, giving us the categories of igneous, metamorphic, and sedimentary rocks. Most characteristics of rocks depend on their constituent minerals. There are also organic rocks, formed through the accumulation of the remains of organisms that decomposed millions of years ago. Coal and some types of carbonate and siliceous rocks are part of this group. HOW TO IDENTIFY ROCKS 62-63 IGNEOUS ROCKS 64-65 MARINE SEDIMENTS 66-67 COLLECTION OF DETRITAL ROCKS 68-69 BEAUTIFUL AND STRANGE The inside of a geode, a rock filled with crystals, usually displays a beautiful formation. ROCKS AND MINERALS 6362 CLASSES OF ROCKS How to Identify Rocks R ocks can be classified as igneous, metamorphic, or sedimentary according to the manner in which they were formed. Their specific characteristics depend on the minerals that constitute them. Based on this information, it is possible to know how rocks gained their color, texture, and crystalline structure. With a little experience and knowledge, people can learn to recognize and identify some of the rocks that they often see. Shapes The final shape that a rock acquires depends to a great extent on its resistance to outside forces. The cooling process and subsequent erosion also influence the formation of rocks. Despite the changes caused by these processes, it is possible to infer information about a rock's history from its shape. Mineral Composition Rocks are natural combinations of two or more minerals. The properties of rocks will change in accordance with their mineralogical composition. For instance, granite contains quartz, feldspar, and mica; the absence of any of these elements would result in a different rock. ROUNDED The wear caused by erosion and transport gives rocks a smooth shape. ANGULAR Rocks have this shape when they have not been worn down. WHITE MARBLE IMPURITY WHITE MARBLE PEGMATITE WHITE MARBLE Fracture When a rock breaks, its surface displays fractures. If the fracture results in a flat surface breaking off, it is called exfoliation. Rocks usually break in locations where their mineral structure changes. Texture refers to the size and arrangement of grains that form a rock. The grains can be thick, fine, or even imperceptible. There are also rocks, such as conglomerates, whose grains are formed by the fragments of other rocks. If the fragments are rounded, there is less compaction, and the rock is therefore more porous. In the case of sedimentary rocks in which the sedimentary cement prevails, the grain is finer. Color The color of a rock is determined by the color of the minerals that compose it. Some colors are generated by the purity of the rock, whereas others are produced by the impurities present in it. Marble, for instance, can have different shades if it contains impurities. GRAIN is the size of the individual parts of a rock, be they crystals and/or fragments of other rocks. A rock's grain can be thick or fine. WHITE If the rock is a marble composed of pure calcite or dolomite, it is usually white. BLACK Various impurities give rise to different shades in the marble. CRYSTALS form when a melted rock cools and its chemical elements organize themselves. Minerals then take the shape of crystals. 0.4 inch (1 cm) 0.4 inch (1 cm) Age Being able to accurately determine the age of a rock is very useful in the study of geology. 64 CLASSES OF ROCKS F ormed from magma or lava, igneous rocks can be classified according to their composition. This classification specially takes into account: the relative proportion of silica, magnesium, and iron minerals found in these type of rocks; their grain size (which reveals how fast they cooled); and their color. Rocks that contain silica, along with much quartz and feldspar, tend to have pale colors; those with low silica content have dark colors created by iron and magnesium-containing minerals, such as olivine, pyroxene, and amphiboles. A rock's texture is determined by the configuration of its crystal grains. Igneous Rocks ROCKS AND MINERALS 65 Underground: Plutonic or Intrusive Rocks Rocks of this type formed through the solidification of magma masses deep within other rocks. In general, they have undergone a slow cooling process in the Earth's crust, which has permitted the formation of pure mineral crystals large enough to be seen with the unaided eye. Usually they display a compact structure and have low porosity. Depending on the composition of the magma, there are acidic plutonic rocks (rich in silicon) or basic rocks (with low silicon content). Granite is the most common type of intrusive rock. Extrusive Rocks, Products of Volcanoes Extrusive rocks form through the fast cooling of magma on or near the Earth's surface. Their structure and composition are closely related to the volcanic activity in the areas where they emerge. Because they are typically products of a fast solidification process, they usually have a very fine grain. When they are expelled from a volcano, they do not have a chance to crystallize before they cool, so they acquire a vitreous (glasslike) texture. THE MINIMUM DEPTH AT WHICH GRANITE FORMS 1 mile (1.6 km) THE MOST COMMON SHAPE INTO WHICH BASALT CRYSTALLIZES Hexagon PEGMATITE IS ASSOCIATED WITH THE PRESENCE OF GEMS AND RARE METALS. Index GRANITE This rock is formed by big grains of feldspar, quartz, and mica. Its light- colored components indicate an abundance of silicon and that the rock is acidic. Because of its great resistance to wear, granite is often used as a construction material. PERIDOTITE This rock is mainly composed of olivine (which gives it a greenish color) and pyroxene. It is less than 45 percent silicon and is rich in magnesium, a very light metal. It is abundant in the upper layers of the mantle (at a depth of about 40 miles [60 km]) as a residue of old crust. GABBRO This rock contains ferromagnesian minerals, such as olivine, pyroxene, and augite, which form dark-colored crystallizations, and feldspars, which give a white coloring to some of its parts. Gabbro generally solidifies slowly, leaving it with thick grains. PEGMATITE This very abundant, acidic rock has a mineral composition identical to that of granite. However, its solidification process was very slow, thus enabling its crystals to grow to a size of several feet. PUMICE This rock is produced from lava with a high silicon and gas content, which gives it a foamy texture. This explains its porous consistency—acquired during rapid solidification—which enables it to float in water. BASALT This rock forms most of the oceanic crust. Its low silicon content gives it its characteristic dark color (between blue and black). Its rapid cooling and solidification gives it a very fine grain. Because of its hardness, it is used to build roads; it is not, however, used to make paving stones because it is too slippery. OBSIDIAN This rock is black; its shades vary in accordance with its impurities. Because it undergoes rapid cooling, its structure is vitreous, not crystalline; thus, it is commonly called volcanic glass. Strictly speaking, obsidian is a mineraloid. It was often used to make arrowheads. GRANODIORITE This rock is often confused with granite, but it is grayer since it contains larger numbers of quartz and sodic plagioclase crystals than it does feldspar. It has thick grains and contains dark crystals called nodules. MACROPHOTOGRAPHY OF PINK GRANITE PEGMATITE IS NATURALLY SMOOTH. CRYSTAL JOINED BY VITREOUS MASS MACROPHOTOGRAPHY OF GRANODIORITE GEOMETRIC PRISMS These prisms were formed in the Giant's Causeway (Northern Ireland) through contraction, expansion, and rupture of basaltic lava flows that crystallized gradually. Dikes and Sills: Rocks Formed in Seams Some types of igneous rocks are formed from ascending magma that solidifies in seams or fissures. The resulting sheetlike body of rock is called a dike if it has a vertical orientation or a sill if it has a horizontal orientation. The composition of these rocks is similar to those of intrusive and extrusive rocks. In fact, like dikes and sills, intrusive and extrusive rocks can also form in cracks. However, the manner in which the materials in a sill or dike solidify causes them to form crystalline structures different from those of their volcanic and plutonic relatives. PORPHYRITICS These rocks solidify in two phases. In the first, slower phase, thick phenocrystals form. Then in the second phase, the phenocrystals are dragged along by magma, which causes the formation of smaller, vitreous crystals. The name porphyritic alludes to the color purple. Organic Rocks 70 CLASSES OF ROCKS ROCKS AND MINERALS 71 O rganic rocks are composed of the remains of living organisms that have undergone processes of decomposition and compaction millions of years ago. In these processes, the greater the depth and heat, the greater the caloric power and thermal transformation of the rock. The change experienced by these substances is called carbonization. OF THE PRIMARY ENERGY CONSUMED IN THE WORLD COMES FROM COAL. 26% Transformation of Vegetation into Hard Coal Vegetation Organic compounds on the surface became covered by oxygen-poor water found in a peat bog, which effectively shielded them from oxidation. 1. Peat Through partial putrefaction and carbonization in the acidic water of the peat bog, the organic matter changes into coal. 2. Lignite is formed from the compression of peat that is converted into a brown and flaky substance. Some primary plant structures can still be recognized in it. 3. Coal has a content of less than 40 percent mineral substance on the basis of dry material. It has a matte luster, is similar to charcoal, and is dirty to the touch. 4. Anthracite is the type of coal with the greatest concentration of carbon. Its high heat value is mostly due to this type of coal's high carbon content and low concentration of volatile material. It is harder and denser than ordinary coal. 5. Coal Formation Plant materials, such as leaves, woods, barks, and spores, accumulated in marine or continental basins 285 million years ago. Submerged in water and protected from oxygen in the air, this material slowly became enriched with carbon through the action of anaerobic bacteria. Contains 95% carbon Contains 80% carbon Contains 70% carbon Contains 60% carbon Vegetation that will form peat after dying Peat is compacted and transformed. Coal rich in humic acids Coal: gas and fuel is obtained Metamorphism where gases and oils are released SURROUNDING TEMPERATURE Exerted Pressure. LEGEND up to 1,000 feet (300 m) DEPTH up to 77º F (25º C) TEMPERATURE 1,000 to 5,000 feet (300 to 1,500 m) DEPTH up to 104° F (40° C) TEMPERATURE 5,000 to 20,000 feet (1,500 to 6,000 m) DEPTH up to 347° F (175° C) TEMPERATURE 20,000 to 25,000 feet (6,000 to 7,600 m) DEPTH up to 572° F (300° C) TEMPERATURE WORLD COAL RESERVES Billions of tons Asia Pacific 296.9 Middle East 0.4 Europe and Eurasia 287.1 North America 254.4 Africa 50.3 Central and South America 19.9 WORLD PETROLEUM RESERVES Billions of barrels Asia Pacific 40.2 Middle East 742.7 Europe and Eurasia 140.5 North America 59.5 Africa 114.3 Central and South America 103.5 LOCATION INSIDE THE EARTH The movements of the Earth's crust subjected the strata rich in organic remains to great pressure and transformed them into hard coal over the course of 300 million years. FORMATION OF PETROLEUM In an anaerobic environment at a depth of about 1 mile (2 km), organic sediments that developed in environments with little oxygen turn into rocks that produce crude oil. KEY Gas Petroleum (Oil) Water At times, the surface of anthracite can appear to have traces of plant fossils. ANTHRACITE ROCK SALINE DOMESTRATIGRAPHIC TRAP ANTICLINE FAULT TRAP PETROLEUM TRAPS Caprock Storage Rock Marble and Quartzite These rocks are compacted and nonfoliated. Marble is a thick-grained crystalline rock, derived from limestone or dolostone. Because of its color and toughness, marble is used in the construction of large buildings. Quartzite is a very hard rock, usually made of sandstone rich in quartz, which, under elevated metamorphic conditions, melts like pieces of glass. Quartzite is normally white, but iron oxide can give it a reddish or pinkish tone. QUARTZITE It is hard and tough; it is compacted because the quartz grains entwine. 7 IS THE LEVEL OFHARDNESS OFQUARTZITE. ROCKS AND MINERALS 7372 CLASSES OF ROCKS Common Metamorphic Rocks Slates and Phyllites These foliated rocks recrystallized under moderate pressure and temperature conditions. Slate has very fine grains made of small mica crystals. It is very useful in the production of roof tiles, floor tiles, blackboards, and billiard tables. It almost always is formed through low-grade metamorphism in sediments and, less often, from volcanic ash. Phyllite represents a gradation in metamorphism between slate and schist; it is composed of very fine mica crystals, such as muscovite or chlorite. Gneiss Striped rock that usually contains long and granular minerals. The most common types are quartz, potash feldspar, and plagioclase. It can also have smaller amounts of muscovite, biotite, and hornblende. Its characteristic stripes are due to a segregation of light and dark silicates. Gneiss rock, which has a mineral composition similar to that of granite, is formed through sedimentary processes or derived from igneous rocks. However, it can also form through high-grade metamorphism of schists. It is the last rock of the metamorphic sequence. Foliation SLATE Its black color comes from the carbon in organic matter present in sediments. SLATE Because of exfoliation, it tends to break into flat sheets. HORNBLENDE SCHIST It contains some sodium as well as considerable amounts of iron and aluminum. MICACEOUS SCHIST Its characteristic coloring is determined by colorless or white muscovite crystals. PHYLLITE Similar to slate, it is notable for its silky luster. LAMINATED OR STRIPED TEXTURE, RESULTING FROM THE PRESSURE TO WHICH THE ROCK WAS SUBJECTED Stripes MAKE IT POSSIBLE TO DETERMINE THE DIRECTION IN WHICH PRESSURE WAS EXERTED ON THE ROCK. 0.04 inch (1 mm) OR MORE. THE SIZE OF MICA GRAINS IN SCHIST—LARGE ENOUGH TO SEE WITH THE UNAIDED EYE. MARBLE It is highly valued for its texture and color. It is used in sculpture and architecture. GARNETIFEROUS SCHIST This rock's name comes from its components. Schist determines its texture and garnet its color and distinctive features. Schist This rock is more prone to foliation, and it can break off in small sheets. It is more than 20 percent composed of flat, elongated minerals, which normally include mica and amphiboles. For schist to be formed, a more intense metamorphism is needed. The different schistose rocks' names and characteristics depend on the predominant mineral that composes them or on the one that produces exfoliation. Among the most important schistose rocks are mica, hornblende, and talc. Because this type of rock has different layers, it has been used in sculpture. GARNETIFEROUS SCHIST The dark red crystals of garnet formed during metamorphism. MARBLE MICROGRAPH Impurities and accessory minerals color the marble. SLATE MICROGRAPHY Composed of foliated or laminated clay minerals GNEISS Heat and pressure can change granite into gneiss. T he classification of metamorphic rocks is not simple because the same conditions of temperature and pressure do not always produce the same final rock. In the face of this difficulty, these rocks are divided into two large groups, taking into account that some exhibit foliation and others do not. During the transformation process, the density of rock increases, and recrystallization can induce the formation of bigger crystals. This process reorganizes the mineral grains, resulting in laminar or banded textures. Most rocks derive their color from the minerals of which they are composed, but their texture depends on more than just their composition. Incredible Petra 74 CLASSES OF ROCKS ROCKS AND MINERALS 75 H istorians from ancient Rome used to talk about a mysterious city of stone. In 1812 Johann Ludwig Burckhardt of Switzerland rediscovered it. Traces of Neolithic civilizations were found in Petra; however, its foundation in the 4th century BC is attributed to the Nabataeans, a nomadic people. The Nabataeans were merchants and raiders who became prosperous by controlling the spice trade. The city, carved in sandstone, knew times of splendor, but it eventually fell into ruin. WINGED LIONS (Interpretation) These carvings were located in the temple of Atargatis, goddess of fertility in the Nabataean culture. ELEPHANTS (Interpretation) Native to Africa or India, elephants were not represented in classic culture. Here, however, they are seen adorning Greek- style capitals. This particular merging of cultures created expressions found nowhere else in the ancient world. Archaeologists find it difficult to date the pieces of art found in Petra. CORINTHIAN CAPITAL (Interpretation) One of the most classic capitals of Greek architecture, along with the Ionic and Doric styles SERAPIS God of prosperity and concealed mysteries. In Egyptian iconography, Serapis has horns. HIDDEN IN THE DESERT Uncertain Origins Petra's architecture is dominated by Greek, Egyptian, and Roman features; however, their symbiosis with Eastern elements is so great that to this day experts find it difficult to establish Petra's origin and dates of construction. The city's exterior adornments contrast with the interior sobriety of its temples. It contained sumptuous public baths that date from a time of splendor (1st century BC). However, most of Petra's population, which reached a peak of 20,000 inhabitants, lived in adobe houses. Temples and Tombs The only way to reach Petra is by foot through a narrow passage among the rocks. The passage is 1 mile (1.5 km) long and, at some points, less than 3.3 feet (1 m) wide. The Treasury (Khasneh) is the first seen upon entering the city, followed by a Roman amphitheater. The buildings are carved into cliffs, and more than 3,000 old tombs have been excavated. The city also has fortifications. Carved in Stone The construction over sandstone respects and takes advantage of the characteristics of the landscape. To create openings, builders used the cracks and fissures that already existed in the rock. The sandstone in Petra is composed of at least two original types of sediments of different colors. Some people believe they are from different geologic phases, but it is more likely that the original sand was made of different grains. A Door Between Worlds The statue represents the god Serapis, whose cult was established in the 4th century BC in both Greece and Egypt. Serapis is of Greek origin, but obelisks and cubic stones, typical Egyptian monuments, also abound in Petra. For a long time, it was believed that Petra was the biblical town of Edom. Its strategic location made it a transit area for Indians and Africans. The Roman and Byzantine empires had a profound influence: Petra was their gateway to the East. Beginning in the 7th century, though, Nabataean culture began to merge with Islamic culture, and it ultimately disappeared. Petra On the Rift ITS CLIFFS ARE PART OF THIS FRACTURE; IN THE YEAR 363, IT WAS DAMAGED BY AN EARTHQUAKE. The Treasury IT WAS BELIEVED THAT THIS BUILDING HOUSED A PHARAOH'S TREASURE. ITS CUBE-SHAPED INTERIOR HAS SMOOTH WALLS AND IS LINED WITH MORTUARY CHAMBERS. SANDSTONE A sedimentary rock with medium-sized grains (less than 0.08 inch [2 mm]), with great toughness and hardness. Its mineralogical composition can vary. In the Jordanian desert, it forms cliffs. TREASURYMOUNT EL KUBHTA MOUNT UM AL BIERRA 3 MILES (5 KM) ORIGINAL WALLS BYZANTINE WALLS CHRISTIAN TOMBS MAIN STREET HABIS CASTLE GREAT TEMPLE AMPHITHEATER Tourist Attraction The stone buildings were erected at different times over a period of 1,000 years. Petra is hidden in the mountains 155 miles (250 km) south of Amman, the capital of Jordan, and north of the Red Sea and the Great Rift Valley in Africa. 80 USE OF ROCKS AND MINERALS F rom the decision to exploit an area where valuable minerals are suspected to exist to obtaining these minerals in major amounts, large-scale mining operations require complex work that lasts for years. For instance, the exploitation of Veladero, an open-air gold-and-silver mine located in the province of San Juan in the Argentinean Andes and exploited by the Canadian company Barrick Gold, required more than a decade of research and development before the first ingots were obtained in October 2005. To reach the deposits, roads and housing were built for the workers. The potential environmental impact of the mine was analyzed since explosives had to be used and toxic substances, such as cyanide, were needed for extracting and separating the rock from other metals. Mountains of Gold and Silver ROCKS AND MINERALS 81 PROSPECTING 1 TO 3 YEARS COST: $10 MILLION Prospecting began in 1994. During this phase, the possible existence of a deposit covering a vast area was analyzed. It was necessary to draw maps, conduct studies, make satellite images, and undertake field trips to analyze superficial rocks. 1. 2. BLUEPRINT OF THE MINE 2 TO 5 YEARS COST: $547 MILLION Once the reserves and costs were analyzed, it was necessary to open the mineral deposit and evaluate the environmental impact of the operation. The infrastructure was then built; it included paths, houses, and river diversions. 3. EXPLOITATION 2 TO 5 YEARS COST: $90 MILLION The first phases are involved with field prospecting. During this process, preliminary research is confirmed or revised. Once the existence of the deposit is confirmed, the next step is to establish its dimensions, reserves, yield, and extraction costs. VELADERO, ARGENTINA Latitude 29° S Longitude 70° W Total land area Employed builders (peak) Gold reserves (1st estimate) Estimated life span 5,000 900 tons 17 years 1,158 square miles (3,000 sq km) GRINDING SYSTEM MACHINERY WAREHOUSE With capacity to store big vehicles Leaching Ground (Potrerillos Ravine) HERE GOLD IS SEPARATED FROM THE ROCKS. GOLD IS NOT FOUND IN METALLIC FORM BUT RATHER COMBINED WITH OTHER MINERALS. OPEN CUT II (AMABLE EDGE) OPEN CUT I (FEDERICO EDGE) VELADERO HILL VELADERO MINE EXPLORATORY PERFORATION VISUAL ANALYSIS OF ROCKS PROCESSING PLANT SAN JUAN ABOVE SEA LEVEL The elevation of the mine (4,000 m) 13,120 feet STRATA Based on these features, geologic maps of the area are drawn. DIRECT OBSERVATION Geologists visit the area and take rock samples. SUPERFICIAL ROCKS During prospecting, field samples are collected for analysis. FEASIBLE AREA Opened by means of perforations and explosions NONPRODUCTIVE AREA Areas that do not yield satisfactory mining results MINERAL CONCENTRATION is evaluated by taking samples from deep in the Earth. PERFORATION TOWER Used to extract rocks located deep within the Earth ENCAMPMENT Sturdy buildings at 12,470 feet (3,800 m) above sea level 164 FEET (50 M) HUGE OPEN-AIR MINE Veladero—located in the Argentinean province of San Juan, as shown on the map—required 2,300 tons of metallic structures and consumes 2,520 tons of sodium cyanide per year for extracting gold. 82 USE OF ROCKS AND MINERALS T here are many types of mines. Some are located in the depths of the Earth, and some show their contents at its surface. Bingham Canyon, a copper mine located in Utah, is not only one of the most important open-air mines but also one of the largest excavations in the world. It is so large that it can be seen from space. It has been in operation since 1903, and it has been excavated in the form of terraces, like those used in agriculture. Its activity never stops, continuing even on weekends and holidays. The manner in which copper is extracted involves not only the use of machinery of extraordinary dimensions but also the use of a hydro-metallurgic chemical process called lixiviation, or leaching. Thanks to this process it is possible to obtain 99.9 percent of copper in its pure state from a copper concentration of 0.02 ounce per pound (0.56 gram per kg) of raw material. ROCKS AND MINERALS 83 1 2 3 How the Metal Is Extracted TERRACING OF THE SURFACE The mine acquires a steplike shape because it is excavated in spiral terraces. The machines can move easily over the terraces, collecting the extracted material. PATHS The roads are well built, and they can withstand loads of up to 1,765 cubic feet (50 cu m) of rock on only one truck. LOADERS/CHARGERS TUNEL RAW MATERIAL The material extracted from the pit is loaded on a mobile grinder. TRANSMISSION PULLEYS SPRINKLERS COLECTOR SEWER ACID SOLUTION 26 FEET (8 M) 2.5 MILES (4 KM) 0.4 MILE (0.7 KM) ELECTROLYTIC POOL COPPER SHEETS BOTTOM OF THE MINE TERRACES MAXIMUM PHREATIC LEVEL BINGHAM CANYON UNITED STATES Latitude 40° 32´ N Longitude 112° 9´ W Diameter of the pit Depth of the pit Opening year Closing year Number of employees 2.5 miles (4 km) 2,300 feet (700 m) 1903 2013 1,700 HOW MATERIAL IS OBTAINED The process begins with rock perforation and blasting. The rock is removed from the pit and loaded by large shovels onto trucks. Then it is unloaded onto a mobile grinder. The ground rock is removed from the mine on conveyor belts and then sprayed with a solution of water and sulfuric acid. ARRANGEMENT OF THE STACK When on the conveyor belts, the material is taken to a place where it will form a lixiviation pile or stack, and a trickle irrigation system is installed on top of this pile. Sprinklers cover the entire exposed area. The material will spend 45 days here. COPPER RECOVERY The resulting copper solution is collected in conduits and then undergoes a process of electrolytic refining. During this process, electricity passes between two copper plates suspended in the solution; copper from the solution adheres to the sheets as it is separated through electrolysis.6 ounces/ gallon (45 g/l) OF COPPER IN THE SOLUTION AT THE END OF THE LIXIVIATION PROCESS COPPER CONCENTRATION IN THE RAW MATERIAL 0.56 % 99.9 % COPPER IN A PURE STATE FORMATION OF THE MINE Surface mines take the shape of large terraced pits, which grow ever deeper and wider. Viewed from above, an enormous spiraling hollow can be seen. This is a relatively inexpensive and simple method to extract high-purity materials. LIXIVIATION The hydro-metallurgic process that makes it possible to obtain copper from the oxidized minerals by applying a solution of sulfuric acid and water. Oxidized minerals are sensitive to attack by acid solutions. Thousands of pounds of explosives, trucks and shovels as large as a house, and massive grinding machines that can reduce hard rocks to dust are involved in the extraction process, and rock temperatures are raised to 4,500° F (2,500° C). In this way, copper is extracted from one of the largest open-air mines on the planet. The raw material excavated from the terraces in the mine contains oxidized copper minerals. This material is transported to grinders, which produce rock fragments 1.5 inches (4 cm) in diameter. These materials are placed in a pile that is treated with a solution of water and sulfuric acid. This process is called lixiviation, or leaching. Lixiviation is a hydro-metallurgic treatment that makes it possible to obtain copper present in the oxidized minerals. The treated material begins the process of sulfatation of copper contained in the oxidized minerals. WATER BASIN The phreatic layer, the closest aquifer to the surface below the water table, emerges at the bottom and forms a water basin with a peculiar color because of the copper salts in the deposit. An Open-Air Mine 84 USE OF ROCKS AND MINERALS Blinded by Brilliance ROCKS AND MINERALS 85 UNITED STATES California Sacramento River 1 1848 On the morning of January 24, while James Marshall was building a sawmill for his employer John Sutter, he discovered gold on the banks of the Sacramento River. This irrevocably changed the history of California. 2 3 1850 California became the 31st state of the Union. Slavery was abolished because of the large influx of immigrants and the fear that it would reduce workers' salaries. However, the Fugitive Slave Act was sanctioned by the state. According to this law, every fugitive slave that entered California had to be returned to his or her owner. 1852 When the surface gold was exhausted, more complex technology was required to extract it from the ground. Hydraulic mining, which used water jets, was a technique used for this purpose. Miners then became employees, enduring long workdays. PARTICLES BEING WASHED WASHED PARTICLES DRAGGING Mules dragged large stones, used to break other quartz stones, thus releasing the gold within. SLOPE The water flowed and deposited gold at the serrated bottom. SLUICE BOX Water flowed through the artificial canal, where riffles (barriers) along the bottom of the sluice box caught the gold and let the other material pass through. THEY SHOVELED THE GRAVEL. CHINESE Chinese immigrants, attracted by the prospect of wealth, constituted most of the labor force. PAN The swirling movement of the pan allowed for the separation of sediments, and the gold could be identified by a difference in weight. DRY RIVER In 1853, $3 million was invested to change the course of the Yuba River, which merged with the Sacramento River. The water of the new canal was used to wash the gold. GOLD IN THE SOIL Gold could be found in dry riverbeds as dust, as nuggets, or as small rock fragments. HOPPER The gravel was placed in the hopper and the deposited material was moved with a lever. When water was added, the dirt could be carried away, leaving the gold at the barrier since the density of gold is greater than that of water. RETURN TO THE RIVER Once the water had been used to pan for gold, it was channeled back into the river from which it came. ARTIFICIAL CANAL BY HAND Resources and tools were scarce. Almost everything was done by hand. ENCAMPMENTS Bad living conditions led to the death of many workers; many were also killed by epidemics and illnesses. DRY RIVERBED CHANNELED RIVER DRY RIVERBED FLOW OF IMMIGRANTS In 1848, California had a population of 14,000. However, within four years and with the gold fever at its peak, the population rose to 223,856. RÍO SA CR AM EN TO 100 SLUICE BOXES COULD BE USED IN THE CONSTRUCTION OF JUST ONE WASHER. $500 MILLION IN GOLD WAS EXCHANGED DURING THE ENTIRE DECADE. $16 WAS THE PRICE OF A PLOT OF LAND; 18 MONTHS LATER, IT WAS PRICED AT $45,000. GOLD SELECTOR ORIGINAL RIVERBED By Boat 40,000* Through Mexico 15,000 From the United States 30,000 Key *Number of immigrants who arrived in 1849 WASHING CONTAINERS T he discovery of gold in the Sacramento River in California in the mid-19th century started one of the largest migrations of its time. Fortune hunters came from the Americas as well as from Asia, but few were able to achieve their goal of striking it rich. Each year, obtaining gold required a larger investment of time and equipment, and equipment suppliers were the ones who ultimately earned the highest profits. Gold was the key force in settling California, now the wealthiest state in the United States. At its peak, immigration overwhelmed the state's social and municipal services as up to 30 houses were being built each day. 90 USE OF ROCKS AND MINERALS ROCKS AND MINERALS 91 U ranium and plutonium were used for the first time—for military purposes—in the 1940s. Once World War II ended, nuclear reactors and their fuels began to be used as sources of energy. To process these minerals, nuclear plants are necessary. They must be built following many safety guidelines, since nuclear energy is considered to be very risky. Accidents like the one in Chernobyl and, more recently, in Tokaimura, Japan, are clear examples of what can happen when control of this form of energy is lost. These images show the structure and heart of a nuclear reactor, the way uranium is processed, and the peaceful uses of this type of energy. FUEL RODS IN EACH GROUP 264 THE NUCLEUS OF THE REACTOR is in the lower part of the safety vessel, in which there are about 200 groups of fuel sheaths sized 0.4 inch (1 cm) in diameter and 13 feet (4 m) in height. USE OF URANIUM IN MEDICINE The application of nuclear energy helps with the diagnosis and treatment of diseases such as cancer. It can detect alterations long before symptoms develop clinically, which allows for more effective early treatment. REACTOR BUILDING This special building is made of reinforced concrete and steel. It is 210 feet (64 m) high and 148 feet (45 m) wide. It houses and shelters the components of the reactor. It also contains the pressure vessel, four steam generators, a pump (which circulates cooling water around the core), and a compressor (which keeps the water under pressure). URANIUM HANDLING Uranium 235 is the only isotope that is found in a natural state, easily fissionable. For this reason, it is the main fuel used in nuclear power plants. Even though it is rare to find it in the Earth's crust, it can be found in enriching deposits in watercourse beds. Radioactive Minerals PROTECTION GLOVES RAW URANIUM GROUPS OF FUEL RODS THAT GENERATE THE NUCLEAR REACTION CONTROL RODS Human Scale WATER DEPOSIT WATER URANIUM PELLETS FOR USE IN A FUEL ROD Pressure Vessel The nuclear reactor is inserted into a vessel formed by steel that is approximately 1.6 feet (0.5 m) thick. The fuel, which is encapsulated in zirconium alloy sheaths, is located inside the hollow space of the vessel. This design helps to meet one of the first goals in nuclear safety: to prevent radioactive products from leaking into the surrounding environment. Carbon 14 is a method for dating organic fossil samples based on the exponential decay law of radioactive isotopes. After a living organism has been dead for 5,730 years, the amount of 14C present in its body has decreased by half. Thus, when the amount of latent 14C is measured in organic materials, it is possible to calculate the amount remaining in the material and, therefore, to calculate when the organism died. PIPING TUNNEL CONTAINER FOR THE FUEL RODS COOLING- FLUID PUMP CRANE BRIDGE CRANE FOR THE FUEL RODS HOOKS TO LIFT OR LOWER THE CONTROL RODS MACHINERY ROOM PIPING TUNNEL STEAM GENERATOR STEEL STRUCTURE THYROID TAKES IN 99MTC-PERTECNETATE. MAMMOTH CUB THYROID SCINTILLOGRAPHY USING POSITRON EMISSION TOMOGRAPHY THE TEMPERATURE OF THE WATER PELLET 572º F (300º C) REINFORCED CONCRETE WALL REINFORCED CONCRETE WALL SAFETY SUIT To handle radioactive material, such as spent fuel bars, workers must wear a special suit because of the high levels of radiation. THE HANDS MUST BE PROTECTED WITH INSULATING GLOVES. THE WORKER CARRIES AN OXYGEN TANK. A HOSE IS CONNECTED TO THE TANK SO THE WORKER CAN BREATHE. THE SUIT IS HERMETIC. IT MUST ISOLATE THE WORKER FROM THE OUTSIDE. 50,000 years U R A N IU M R O D S REACTOR CORE 92 GLOSSARY ROCKS AND MINERALS 93 Glossary Alkalines Minerals that have a high content of potassium, sodium, lithium, rubidium, and calcium. Amorphous Mineral with fractured surfaces instead of crystalline faces. Noncrystalline. Anticline A fold of sedimentary strata sloping upwards like an arch. Asthenosphere Layer inside the Earth, below the lithosphere. It is part of the upper mantle and is composed of easily deformable rock. Atom The smallest unit of matter. Bacteria Microscopic and unicellular life-form found in air, water, plants, animals, and on the Earth's crust. Batholith Great mass (larger than 60 square miles [100 sq km] of surface) of intrusive igneous rocks. Bravais Lattices Three-dimensional crystal systems, based on certain mathematical principles, that represent the 14 types of cell units. Butte Hill with a flat top and sloping sides, found in areas that have undergone intense erosion. Canyon Deep, narrow valley formed by fluvial erosion. Carat Unit of weight used in jewelry, variable in time and place, equivalent to 0.007 ounce (0.2 g). Cave Subterranean cavity formed through the chemical action of water on soluble, generally calcareous, ground. Cementation Process by which sediment both loses porosity and is lithified through the chemical precipitation of material in the spaces between the grains. Cementation Zone Place where lithification occurs. Water infiltrates the area, fills up the spaces between the grains of sediment, and transforms loose sediment into a solid mass. Chasm, or Rift Wide valley formed as a consequence of the extension of the crust at the boundaries of diverging tectonic plates. Chemical Compound Substance formed by more than one element. Chemical Element Substance that contains only one type of atom. Clay Fine-grained sediments formed by the chemical decomposition of some rocks. It is malleable when wet and hardens as it dries. Coal Combustible black rock of organic origin. It is produced through the decomposition of plant materials that accumulate in swamps or shallow marine waters. deposit is called primary. Otherwise, it is called secondary. Diatomite Light, porous rock. It has a light color, and it is consolidated. Composed exclusively (or almost) of diatoms. Dolostone Carbonated sedimentary rock that contains at least 50 percent or more carbonate, of which at least half appears as dolomite. Earthquake The sudden and violent release of energy and vibrations in the Earth that generally occurs along the edges of tectonic plates. Elasticity Tendency of a mineral to recover its shape after being subjected to flexion or torsion. Era Division of time in the Earth's history. Geologists divide eras into periods. Erosion Removal and transport of sediment through the action of water, ice, and wind. Evaporation Process through which a liquid becomes gas without boiling. Exfoliation The tendency for certain minerals to fracture along regular planes within their crystalline structure. Fault Fracture involving the shifting of one rock mass with respect to another. Flexibility Ability of minerals to bend without fracturing. Fluorescence Property of some minerals that enables them to emit a certain level of light when exposed to ultraviolet rays. The fluorescent properties present in a metal can make it look as if it were truly fluorescent. Fold Bending and deformation of rock strata due to the compression caused by the movements of tectonic plates. Fossil Any trace of an old life-form. It can be the petrified remains of an organism or an impression of an organism left in rock. Fossil Fuel Fuel formed from the partially decomposed remains of deceased organisms. These mixtures of organic compounds are extracted from the subsoil with the goal of producing energy through combustion. They are coal, oil, and natural gas. Fracture Break of a mineral along an irregular surface. It can be conchoidal, hooked, smooth, or earthy. Gem Mineral or other natural material that is valued for its beauty and rarity. It can be polished and cut to produce jewels. Geode Spherical, rocky cavity covered with well- formed crystals. Geology Study of the Earth, its shape, and its composition. Rocks, minerals, and fossils offer information that helps us reconstruct the history of the planet. Glacier A large mass of ice formed through the accumulation of recrystallized and compacted snow occurring either on a mountain or over a large area on a landmass. Ice moves slowly and both excavates rock and carries debris. Granite Intrusive igneous rock composed mainly of quartz and feldspar. It can be polished and used in decoration. Habit External aspect of a crystal that reflects its predominant shape. Hardness Resistance offered by a mineral to scratching and abrasion. One mineral is said to be harder than another if the former can scratch the latter. Hot Spot Place within a tectonic plate where active volcanoes form. Hydrothermal Process involving the physical and chemical transformations suffered by rocks or minerals through the action of hot fluids (water and gases) associated with a magma body. Igneous Rocks Rocks formed directly from the cooling of magma. If they solidify inside the crust, they are said to be plutonic (or intrusive); if they solidify on the surface, they are said to be volcanic (or extrusive). Impermeable Rock Rock through which liquids cannot be filtered. Concretion Hard mass of mineral material that usually holds a fossil inside. Contact Metamorphism Large-scale transformation of a rock into another type of rock. This happens mostly as a consequence of a sudden temperature increase. Convection Currents Moving pathways of material that occur inside the mantle as a consequence of the transfer of heat coming from the Earth's core. The hottest zones of the mantle rise, and the coldest ones sink. These movements are probably responsible for the movement of tectonic plates. Crack Fissure or cavity in the rock that results from tension. It can be completely or partially filled with minerals. Crust External layer of the Earth. There are two types of crust: continental crust forms large terrestrial masses, and oceanic crust forms the bottoms of the oceans. Crystal Organized, regular, and periodically repeated arrangement of atoms. Crystalline System It includes all crystals that can be related to the same set of symmetric elements. Density Amount of mass of a mineral per unit of volume. Deposit A natural accumulation of a rock or mineral. If it is located at the site where it formed, the 94 GLOSSARY ROCKS AND MINERALS 95 Intrusion A large mass of rock that forms in empty spaces underground when magma infiltrates strata, cools, and solidifies. Jade White or green metamorphic rock formed by a compact and tenacious filter of very fine needles of tremolite. It is a rare rock used in art objects. Karst Cycle Formation cycle of caves that lasts a total of about one million years. Kimberlite Type of rock usually associated with diamonds and other minerals coming from the depths of the Earth. Lava Magma expelled on the surface of the Earth. Limestone Rock containing at least 50% calcite. It can also have dolomite, aragonite, and siderite. Lithosphere Exterior, rigid layer of the Earth formed by the crust and upper mantle. Lode Sub-superficial rock intrusion of tabular-shaped rock. Luster Level of light reflection on the surface of a crystal. Magma Hot, rocky material from the crust and upper mantle in liquid state that forms crystals as it cools. When magma is expelled at the Earth's surface, it is called lava. Magmatic Rock Rock that forms when magma cools off and solidifies. Magmatic intrusive rocks solidify underground, while the extrusive ones solidify on the surface. Magnetism Property of some minerals that allows them to be attracted by a magnet and to change the direction of a compass needle. Malleability Mechanical property of a mineral that makes it possible for the mineral to be molded and formed into a sheet through repeated blows without breaking. Mantle The layer between the crust and external core. It includes the upper mantle and lower mantle. Marble Metamorphosed limestone rock composed of compacted calcite and dolomite. It can be polished. Massive One of the possible habits of a consistent mineral that refers to the tendency for certain crystals to intertwine and form a solid mass rather than independent crystals. Metal Any element that shines, conducts electricity, and is malleable. Metamorphic Rock Type of rock resulting from the application of high pressure and temperature on igneous and sedimentary rocks. Mineral Inorganic solid of natural origin that has an organized atomic structure. Placer Mineral concentrations as deposits of placer during time lapses that vary from a few decades up to millions of years. Pyroelectric Property that some nonconductor minerals have to create difference in power transmissions from differences in temperature. Quartzite Metamorphic rock formed by the consolidation of quartz sandstone. It is extremely hard. Quartzite can also be a sedimentary rock, which is sandstone with a very high content of quartz; it is very hard and it has light color. Regional Metamorphism Metamorphism occurring in rock over large areas. Rock Natural aggregate of one or more minerals (sometimes including noncrystalline substances) that constitute an independent geologic unit. Sedimentary Rock Rock that forms through accumulation of sediments that, when subjected to physical and chemical processes, result in a compacted and consolidated material. Sediment can form on river banks, at the bottom of precipices, in valleys, lakes, and seas. Sedimentary rock accumulates in successive layers, or strata. Sediments Rock fragments or remains of plants or animals deposited at the bottom of rivers, lakes, or oceans by water, wind, or ice. Seismic Waves Elastic waves that travel through the Earth after an earthquake. They can also be produced artificially through explosions. Silicates They make up about 95 percent of the Earth's crust. Their tetrahedral structure, with one silicon and four oxygen ions, creates different types of configurations through the union of the ions. According to their composition, members of this mineral group are differentiated into light and dark. Slate Bluish black, fine-grained metamorphic rock. It can be easily divided into sheets. Solution Mixture of two or more chemical substances. It can be liquid, solid, or gaseous. Stalactite Internal structure of a cave. It is conical and hangs from the cave ceiling. Stalagmite Internal structure of a cave. It is conical and rises from the cave floor. Streak Characteristic color of the fine dust obtained from a mineral by rubbing it over an unglazed porcelain plate. Streak Test A test that involves rubbing a mineral against an unglazed white porcelain sheet to obtain dust. The color of the dust left on the tile can help identify the mineral. Symmetry Axes Symmetry element that enables the repetition of crystalline faces to form different shapes. Syncline Concave fold of sedimentary rock strata. The younger rocks are located at the center of the concave. Talus Slope Accumulation of fragments resulting from the mechanical weathering of rocks. The sediment deposit forms more or less in situ as the result of the transport of materials through gravity over a small distance. Tectonic Elevation Rising of rocks as a consequence of the movements of tectonic plates. Tectonic Plates Rigid fragments of the lithosphere that move on the asthenosphere. Tenacity The level of toughness that a mineral offers to fracture, deformation, crushing, bending, or pulverization. Transparent It is said that a mineral is clear when light goes through it without weakening. When only some light passes through, the mineral is called translucent. If no light passes through, it is called opaque. Vein Fracture that cuts through rocks and is filled by some mineral. Volcanic Outcropping Isolated pile of hard magmatic rocks that remain after the disappearance of the rest of the volcano due to erosion. Weathering The breaking down of a material by sustained physical or chemical processes. Mohs Scale A tool designed to test the hardness of a given mineral by comparing it to 10 known minerals, from the softest to the hardest. Each mineral can be scratched by those following it. Molecule Chemical compound formed when one or several types of atoms are joined together. Native Element An element that occurs in nature that is not combined with other elements. Sulfur and gold are examples of native elements. Oceanic Trench Narrow and deep submarine depression formed when the oceanic crust of one tectonic plate moves beneath another. Ornamental Stone It is not a precious stone, but it can be used in jewelry or for other ornamental purposes. Outcrop Part of a rock formation devoid of vegetation or soil that stands out from the Earth's surface. Oxidation Zone Deposit of minerals with oxidizing properties, formed through the effect of meteorization or weathering. Petrifaction Cell-by-cell replacement of organic matter, such as bones or wood, with minerals of the surrounding solutions. Piezoelectric Property that some minerals have to produce a difference in potential when subjected to compression, traction, or torsion. 100 INDEX ROCKS AND MINERALS 101 piezoelectricity, 25 Pleistocene Epoch, 11 Pliocene Epoch, 11 plutonic rock (intrusive rock), 64 formation, 12, 42 rock cycle, 57 polymorphism, 21 porphyritic rock, 65 positron emission tomography, 91 Precambrian Period, 8 precious stone, colors, 32-33 See also specific types, for example diamond pressure, effect on rock structure, 55 prism, 30 Giant's Causeway, 65 Proterozoic Era, 8 pumice, 65 pyrite (fool's gold) chemical crystallization, 21 structure, 39 pyroclastic material: See volcanic ash pyroelectricity, 25 Quaternary Period, 11 quartz agate, 23 color, 22 composition, 17 hardness, 25 structure, 37 quartzite, 73 R radioactive mineral, 90-91 ranker (soil type), 56 rapids, 48 refining, petroleum, 89 refraction, 23 regional metamorphism, 55 See also metamorphism reptile Cretaceous Period extinction, 10 Mesozoic Era, 10 rhodochrosite, 31 rhombic crystalline system, 31 river, sediment transportation, 48-49 rock, 60-75 color, 62 formation, 16-17, 62 identification, 62-63 mineralogical composition, 62 shape, 62 transformation: See metamorphism See also specific types, for example granite rock crystal, 22 rock cycle, 6-7, 57 Rocky Mountains (North America), formation, 10 Rodinia (early supercontinent), 8 rose quartz, 22 ruby, color, 32 S safety measure, radioactive material, 90, 91 salt (halite), 19, 20 extraction, 27 ionic bond, 28 structure, 21, 28-29 salt deposit, hornito formation, 27 sandstone classification, 69 Petra, 74-75 Uluru, 58-59 sapphire, color, 33 Saudi Arabia, Black Stone of the Ka'bah, 59 scheelite, 31 schist, 55 types, 72-73 Scotland, gneiss formation, 9, 54-55 sediment soil formation, 56 stripe (rock), 72 subsoil, 57 sulfate, 39 sulfide, 39 sulfur, 19, 20, 22 supercontinent, 8, 9 T talc, 37 hardness, 24 Taylor, Elizabeth, 35 Taylor-Burton diamond, 35 temperature, degree of metamorphism, 55 terminal moraine, 47 Tertiary Period, 10-11 tetragonal crystalline system, 31 texture (rock), 63 thyroid, scintillography, 91 till, glaciers, 47 topaz, 31 color, 33 hardness, 25 Torres del Paine National Park (Chile), 16-17 tourmaline, 24-25 transportation, eroded materials, 15 Triassic Period, 10 triclinic crystalline system, 31 trigonal crystalline system, 31 trilobite, 9, 52 tropics, laterite soil, 56 tuff, detrital rocks, 68 tunnel, formation, 51 turquoise, color, 33 U Uluru-Kata Tjuta National Park (Australia), 58-59 unconformity, rock layers, 53 United Kingdom Giant's Causeway, 65 royal family's diamond ownership, 34, 35 United States of America Bingham Canyon, 82-83 Corkscrew Canyon, 6-7, 14-15 gold mining, 84-85 Grand Canyon, 52-53, 66 Mauna Loa volcano, 12-13 Neversink Pit, 40-41 Yosemite National Park, 44-45 Ural Mountains (Eurasia), formation, 9 uranium, 77 handling, 90 medical uses, 91 V Valley of Diamonds (legend), 35 vanadinite, 30 Veladero mine (Argentina), 80-81 Victoria, Queen, Great Koh-I-Noor diamond, 34 volcanic ash, 68 ash cone, 43 volcanic rock (extrusive rock), 65 formation, 12, 42, 43 rock cycle, 57 volcano caldera, 43 Dallol, 18-19, 26-27 Mauna Loa 12-13 rock formation, 42, 65 W water cave formation, 50-51 erosion, 14 hornitos, 26, 27 sediment transportation, 48-49 weathering, 15 waterfall formation, 48 Yosemite National Park, 45 weathering, 14, 15 wind deserts, 46 erosion, 14 sediment transportation, 47 Winston, Harry, 35 X-Z X-ray diffraction, 22 crystal structure identification, 28 Yosemite National Park (United States), 44-45 Yucatán Peninsula (Mexico), meteor, 10 zooxanthellae, coral reefs, 67 fdf dsdfsdaf water transportation, 48-49 wind transportation, 47 sedimentary rock detrital rock, 68-69 formation, 46-49, 57 marine organic remains, 66-67 See also stalactite; stalagmite sedimentation, 15, 48 semimetal mineral, 20 semiprecious stone color, 33 See also precious stone Serapis (Egyptian god), 75 Siberia, Ural Mountains formation, 9 siderite, structure, 21 Sierra Nevada range (United States), 44-45 silicate, structures, 29, 36-37 silicon, 79 sill (rock formation), 42, 65 Silurian Period, 9 silver crystal dendrite, 20 mining, 80-81 sinkhole, 50 slate, 39, 72 formation, 9 micrography, 72 phyllite formation, 54, 72 sluice box, 85 Smithsonian Institution, Hope Diamond, 35 smoky quartz, 22 soil formation, 56 humus, 57 profile, 57 types, 56 South Africa Cango Caves, 50-51 diamonds, 35 stalactite, 50 formation, 51 stalagmite, 50 stock (rock formation), 43 streak color, 23 See also color ca EPTC] AN doar otaitoa
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