Dictionary of Geology

Dictionary of Geology

(Parte 8 de 10)

Mohs scale, and specific gravity is 4.13. { os tə nıt} austral axis pole [GEOPHYS] The southern intersection of the geomagnetic axis with the earth’s surface. { os trəl ¦ak səs pol} australite [GEOL]A tektite found in southern Australia, occurring as glass balls and spheroidal dumbbell forms of green and black, similar to obsidian and probably of cosmic origin. { os trə lıt} Australopithecinae [PALEON] The near-men, a subfamily of the family Hominidae com- posed of the single genus Australopithecus.{ o stra lo pith ə sı ne } Australopithecus [PALEON]A genus of near-men in the subfamily Australopithecinae representing a side branch of human evolution. { o stra lo pith ə kəs} Austrian orogeny [GEOL]A short-lived orogeny during the end of the Early Cretaceous.

{ os tre əno raj ə ne } autallotriomorphic [PETR] Pertaining to an aplitic texture in which all mineral constituents crystallized simultaneously, preventing the development of euhedral crystals.

{ ¦aud ə¦la tre ə¦mor fik } authigene [MINERAL]A mineral which has not been transported but has been formed in place. Also known as authigenic mineral. { o thə jen} authigenic [GEOL]O f constituents that came into existence with or after the formation of the rock of which they constitute a part; for example, the primary and secondary minerals of igneous rocks. { ¦o thə¦jen ik } authigenic mineral See authigene. { ¦o thə¦jen ik min rəl} authigenic sediment [GEOL] Sediment occurring in the place where it was originally formed. { ¦o thə¦jen ik sed ə mənt } autobrecciation [GEOL] The process whereby portions of the first consolidated crust of a lava flow are incorporated into the still-fluid portion. { ¦od o brech e a shən} autochthon [GEOL]A succession of rock beds that have been moved comparatively little from their original site of formation, although they may be folded and faulted extensively. [PALEON]A fossil occurring where the organism once lived. { o tak thən}

Downloaded from : iDATA.ws aventurine autochthonous [GEOL] Having been formed or occurring in the place where found.

{o tak thə nas } autochthonous coal [GEOL] Coal believed to have originated from accumulations of plant debris at the place where the plants grew. Also known as indigenous coal.

{o tak thə nas kol} autochthonous sediment [GEOL]A residual soil deposit formed in place through decomposition. { o tak thə nas sed ə mənt } autoclastic [GEOL]O f rock, fragmented in place by folding due to orogenic forces when the rock is not so heavily loaded as to render it plastic. { ¦od o¦klas tik } autoclastic schist [GEOL] Schist formed in place from massive rocks by crushing and squeezing. { ¦od o¦klas tik shist } autogenetic topography [GEOL] Conformation of land due to the physical action of rain and streams. { ¦od o jə¦ned ik tə pag rə fe } autogeosyncline [GEOL]A parageosyncline that subsides as an elliptical basin or trough nearly without associated highlands. Also known as intracratonic basin. { ¦od o¦je o sin klın} autoinjection See autointrusion. { ¦od o in jek shən} autointrusion [GEOL]A process wherein the residual liquid of a differentiating magma is drawn into rifts formed in the crystal mesh at a late stage by deformation of unspecified origin. Also known as autoinjection. { ¦od o in tru zhən} autolith [PETR] 1. A fragment of igneous rock enclosed in another igneous rock of later consolidation, each being regarded as a derivative from a common parent magma. 2. A round, oval, or elongated accumulation of iron-magnesium minerals of uncertain origin in granitoid rock. { od o lith } autolysis [GEOCHEM] Return of a substance to solution, as of phosphate removed from seawater by plankton and returned when these organisms die and decay. { o tal ə səs} autometamorphism [PETR] Metamorphism of an igneous rock by the action of its own volatile fluids. Also known as autometasomatism. { ¦od o med ə mor fiz əm} autometasomatism See autometamorphism. { ¦od o med ə so mə tiz əm} automorphic [PETR]O f minerals in igneous rock bounded by their own crystal faces.

Also known as euhedral; idiomorphic. { ¦od o¦mor fik } automorphosis [PETR] Metamorphosis of solidified igneous rock by solutions from its heated interior. { od ə mor fə səs} autophytograph [GEOL]A n imprint on a rock surface made by chemical activity of a plant or plant part. { od ə fıd ə graf } autopneumatolysis [GEOL] The occurrence of metamorphic changes at the pneumatolytic stage of a cooling magma when temperatures are approximately 400–600 C.

autunite [MINERAL] Ca(UO2)2(PO4)2 10H2OA common fluorescent mineral that occurs as yellow tetragonal plates in uranium deposits; minor ore of uranium. { o tə nıt}

Auversian See Ledian. { o vərzh ən} auxiliary fault [GEOL]A branch fault; a minor fault ending against a major one.

{og zil yə re folt } auxiliary mineral [MINERAL]A light-colored, relatively rare or unimportant mineral in an igneous rock; examples are apatite, muscovite, corundrum, fluorite, and topaz.

{og zil yə re min rəl} auxiliary plane [GEOL]A plane at right angles to the net slip on a fault plane as determined from analysis of seismic data for an earthquake. { og zil yə re plan} available relief [GEOL] The vertical distance after uplift between the altitude of the original surface and the level at which grade is first attained. { ə val ə bəlr i lef} aven See pothole. { av ən} aventurine [MINERAL] 1. A glass or mineral containing sparkling gold-colored particles, usually copper or chromic oxide. 2. A shiny red or green translucent quartz having

Downloaded from : iDATA.ws average igneous rock small, but microscopically visible, exsolved hematite or included mica particles.

{ ə vench ə ren} average igneous rock [PETR]A hypothetical rock whose composition is thought to be similar to the average chemical composition of the outermost 10-mile (16-kilometer) shell of the earth. { av rij ig ne əs rak} aviolite [PETR]A mica-cordierite-hornfels. { a vı ə lıt} avogadrite [MINERAL] (K,Cs)BF4Anorthorhombicfluoborate mineraloccurringinsmall crystals on Vesuvian lava. { a və gad rıt}

Avonian See Dinantian. { ə von e ən} awaruite [MINERAL] Native nickel-iron alloy containing 57.7% nickel. { a wa ru ıt} axial compression [GEOL]A compression applied parallel with the cylinder axis in experimental work involving rock cylinders. { ak se əlk əm presh ən} axial culmination [GEOL] Distortion of the fold axis upward in a form similar to an anticline. { ak se əl kəl mə na shən} axial dipole field [GEOPHYS]A postulated magnetic field for the earth, consisting of a dipolar field centered at the earth’s center, with its axis coincident with the earth’s rotational axis. { ak se əl di pol feld } axial plane [GEOL]A plane that intersects the crest or trough in such a manner that the limbs or sides of the fold are more or less symmetrically arranged with reference to it. Also known as axial surface. { ak se əl plan} axial-plane cleavage [GEOL] Rock cleavage essentially parallel to the axial plane of a fold. { ak se əl ¦plan kle vij } axial-plane foliation [GEOL] Foliation developed in rocks parallel to the axial plane of a fold and perpendicular to the chief deformational pressure. { ak se əl ¦plan fo le a shən} axial-plane schistosity [GEOL] Schistosity developed parallel to the axial planes of and syncline. { ak se əl ¦plan sep ə ra shən} axial surface See axial plane. { ak se əl sər fəs} axial trace [GEOL] The intersection of the axial plane of a fold with the surface of the earth or any other specified surface; sometimes such a line is loosely and incorrectly called the axis. { ak se əl tras} axial trough [GEOL] Distortion of a fold axis downward into a form similar to a syncline.

axinite [MINERAL]H 2(Ca,Fe,Mn)4(BO)Al2(SiO4)5 Brown, blue, green, gray, or purplish gem mineral that commonly forms glassy triclinic crystals. Also known as glass schorl. { ak sə nıt} axinitization [GEOL] The replacement of rocks by axinite, as in the border zones of some granites. { ak zin ə tə za shən} axiolite [MINERAL]A variety of elongated spherulite in which there is an aggregation of minute acicular crystals arranged at right angles to a central axis. { ak se ə lıt} axis [GEOL] 1. A line where a folded bed has maximum curvature. 2. The central portion of a mountain chain. { ak səs}

Azoic [GEOL] That portion of the earlier Precambrian time in which there is no trace of life. { a zo ik } azonal soil [GEOL] Any group of soils without well-developed profile characteristics, owing to their youth, conditions of parent material, or relief that prevents development of normal soil-profile characteristics. Also known as immature soil. { a zon əl soil } azulite [MINERAL]A translucent pale-blue variety of smithsonite found in large masses azurite [MINERAL]C u3(CO3)2(OH)2 A blue monoclinic mineral consisting of a basic carbonate of copper; an ore of copper. Also known as blue copper ore; blue mala- chite; chessylite. { azh ə rıt} azurmalachite [MINERAL]A mixture of azurite and malachite, usually occurring massive with concentric banding; used as an ornamental stone. { ¦a zhər mal ə kıt}

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back-arc basin [GEOL] The region (small ocean basin) between an island arc and the continental mainland formed during oceanic plate subduction, containing sediment eroded from both. { bak ark bas ən} back beach See backshore. { bak bech } backbone [GEOL] 1. A ridge forming the principal axis of a mountain. 2. The principal mountain ridge, range, or system of a region. { bak bon} backdeep [GEOL]A n epieugeosynclinal basin; a nonvolcanic postorogenic geosyncli- nal basin whose sediments are derived from an uplifted eugeosyncline. { bak dep} backfolding [GEOL] Process in mountain forming in which the folds are overturned toward the interior of an orogenic belt. Also known as backward folding. { bak fold iŋ } backlands [GEOL]A section of a river floodplain lying behind a natural levee. { bak lanz } backlimb [GEOL]O f the two limbs of an asymmetrical anticline, the one that is more gently dipping. { bak lim } back-set bed [GEOL] Cross bedding that dips in a direction against the flow of a depositing current. { bak set bed } backshore [GEOL] The upper shore zone that is beyond the advance of the usual waves and tides. Also known as back beach; backshore beach. { bak shor} backshore beach See backshore. { bak shor bech } backshore terrace See berm. { bak shor ter əs} back slope See dip slope. { bak slop} backswamp [GEOL] Swampy depressedarea ofa floodplainbetween thenatural levees and the edge of the floodplain. { bak swamp } backthrusting [GEOL] The thrusting in the direction of the interior of an orogenic belt, opposite the general structural trend. { bak thrəst iŋ } backward folding See backfolding. { bak wərd ¦fold iŋ } backwash mark [GEOL]A crisscross ridge pattern in beach sand, caused by backwash. { bak wash mark } backwash ripple mark [GEOL] Ripple marks that are broad and flat and parallel to the shoreline, with narrow, shallow troughs and crests about 30 centimeters apart; formed by backwash above the maximum wave retreat level. { bak wash rip əl mark } baculite [GEOL]A crystallite that looks like a dark rod. { bak yə lıt} baddeleyite [MINERAL] ZrO2 A colorless, yellow, brown, or black monoclinic zirconium oxide mineral found in Brazil and Ceylon; used as heat- and corrosion-resistant linings for furnaces and muffles. { bad əl e ıt} bahada See bajada. { bə had ə } bahamite [PETR]A consolidated limestone formed of sediment similar to a type currently found accumulating in the Bahamas. { bə ham ıt} bahiaite [PETR] Holocrystalline igneous rock formed mainly of hypersthene with subordinate hornblende and sometimes minor amounts of other minerals. { bə hı yə ıt} baikerite [MINERAL]A waxlike mineral from the vicinity of Lake Baikal, Siberia; apparently about 60% ozocerite with other tarry, waxy, and resinous hydrocarbons. { bı kə rıt}

Downloaded from : iDATA.ws bajada bajada [GEOL]A n alluvial plain formed as a result of lateral growth of adjacent alluvial fansuntiltheyfinallycoalescetoformacontinuousinclineddepositalongamountain front. Also spelled bahada. { bə had ə } bajada breccia [PETR]A n imperfectly stratified accumulation of coarse, angular rock fragments mixed with mud that formed in arid climates and results from a mudflow containing considerable water. { bə had ə brech ə }

Bajocian [GEOL]A European stage: the middle Middle or lower Middle Jurassic geologic time; above Toarcian, below Bathonian. { bə jo shən} bakerite [MINERAL] 8CaO 5B2O3 6SiO2 6H2O White mineral, occurring in fine-grained, nodular masses, resembling marble and unglazed porcelain, and consisting of hydrous calcium borosilicate. { bak ə rıt} balanced rock See perched block. { bal ənst rak} baldheadedanticline [GEOL]A nupfoldwithacrestthathasbeendeeplyerodedbefore later deposition. { bold hed əd an ti klın} ball [GEOL] 1. A low sand ridge, underwater by high tide, which extends generally parallel with the shoreline; usually separated by an intervening trough from the beach. 2. A spheroidal mass of sedimentary material. 3. Common name for a nodule, especially of ironstone. { bol} ball-and-socket joint [GEOL] See cup-and-ball joint. { ¦bol ən sak ət joint } ballas [MINERAL]A spherical aggregate of small diamond crystals; used in diamond drill bits and other diamond tools. { bal əs} ball coal [GEOL]A variety of coal occurring in spheroidal masses. { bol kol} ballstone [GEOL] 1. Large mass or concretion of fine, unstratified limestone resulting from growth of coralcolonies. 2. A nodule of rock, especiallyironstone, in a stratified unit. { bol ston} balm [GEOL]A concave cliff or precipice that forms a shelter. { bam} banakite [PETR]A n alkalic basalt made up of plagioclase, sanidine, and biotite, with small quantities of analcime, augite, and olivine; quartz or leucite may be present. { ban ə kıt} band [GEOL]A thin layer or stratum of rock that is noticeable because its color is different from the colors of adjacent layers. { band } bandaite [PETR]A dacite type of extrusive rock composed of hypersthene and labradorite. { ban də ıt} banded [PETR] Pertaining to the appearance of rocks that have thin and nearly parallel bands of different textures, colors, and minerals. { ban dəd} banded coal [GEOL]A variety of bituminous and subbituminous coal made up of a sequence of thin lenses of highly lustrous coalified wood or bark interspersed with layers of more or less striated bright or dull coal. { ban dəd kol} banded differentiate [PETR]A type of igneous rock made up of bands of different composition, frequently alternating between two varieties as in a layered intrusion.

{ ban dəd dif ə ren che at} banded iron formation [GEOL]A sedimentary mineral deposit consisting of alternate silica-rich (chert or quartz) and iron-rich layers formed 2.5–3.5 billion years ago; the major source of iron ore. { ¦band əd ı ərn for ma shən} banded ore [GEOL] Ore made up of layered bands composed either of the same minerals that differ from band to band in color or textures or proportion, or of different minerals. { ban dəd or} banded peat [GEOL] Peat formed of alternate layers of vegetable debris. { ban dəd pet} banded structure [PETR]A n outcrop feature in igneous and metamorphic rocks due to alternation of layers, stripes, flat lenses, or streaks that obviously differ in mineral composition or texture. { ban dəd strək chər} banded vein [GEOL]A vein composed of layers of different minerals that lie parallel to the walls. Also known as ribbon vein. { ban dəd van} banding [PETR] 1. The series of layers occurring in a banded structure. 2. In sedimentary rocks, the thin bedding of alternate layers of different materials. { band iŋ }

(Parte 8 de 10)