Os minerais minérios em microscópio - Guia optico

Os minerais minérios em microscópio - Guia optico

(Parte 2 de 3)

Since it is very difficult to gather the vast amount of different ore minerals included in this atlas, I am very much indepted to a number of colleagues, who provided many uncommon samples. In particular, the use of Ramdohr’s famous research collection, now held at the Mineralogy Department of Heidelberg University, as well as the samples from the BGR and the private collection of T. Witzke proved to be valuable sources for many specimens. All published photo contributions are thankfully referenced below and cited in the text with the respective abbreviation in square brackets (e.g., [d]).

Abbreviation* [a - c]

[d]

Name Affiliation/Address

Author’s research and Freie Universität Berlin teaching collections

Dr. Frank Melcher & Dr. Thomas Oberthür

Luzerner Str. 10-12, D-12205 Berlin, Germany – Freie Universität Berlin, FB Geowissenschaften, Institut für Geologische Wissenschaften, FR Geochemie, Hydrogeologie, Mineralogie, Malteserstr. 74-100, D-12249 Berlin, Germany Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, D-30655 Hannover, Germany [e]

[f]

[g]

[h]

Dr. Thomas Kenkmann

Prof. Dr. Robert Marschik & Dr. Ana Rieger

Museum für Naturkunde der Humboldt-Uni- versität zu Berlin, Invalidenstr. 43, D-10115 Berlin, Germany Ludwig-Maximilians Universität, Departmen t für Geo- und Umweltwissenschaften, Ressourcengeologie, Luisenstr. 37, D-80333 München, Germany Dr. Thomas Seifert

Dr. Thomas Witzke

TU Bergakademie Freiberg, Institute of Mineralogy, Department of Economic Geology, Brennhausgasse 14, D-09596 Freiberg, Germany Urho-Kekkonen-Str. 9, D-18147 Rostock, Germany [i]

[j]

[k] [l]

Dipl.-Geol. David van Acken

Prof. Dr. Rainer Altherr & Dr. rer. nat. Michael Hanel

Freie Universität Berlin, FB Geowissenschaften, Institut für Geologische Wissenschaften, FR Geochemie, Hydrogeologie, Mineralogie, Malteserstr. 74-100, D-12249 Berlin, Germany Mineralogisches Institut, Universität Heidelberg, Im Neuenheimer Feld 236, D-69120 Heidelberg, Germany

Dr. rer. nat. Erio Rahders

Prof. Dr. Supriya RoyLaubsängerweg 45, D-12351 Berlin, Germany Department of Geological Sciences, Jadavpur

University, Calcutta - 700 032, India [m]

[n] [o]

Dr. rer. nat. Hans-Peter Röper Prof. Dr.-Ing. Peter Halbach

Witzlebenstr. 19, D-14057 Berlin, Germany

Sodenstr. 19, D-12309 Berlin, Germany Dr. Michael QuednauEichenstraße 15, 61476 Kronberg, Germany

*(as cited in the mineral description text)

Instrument Settings

Microscope

Model Lamp Position Filter Aperture Objectives

Camera Model

Optical Zoom Objektive

Picture Size/Quality* Rotation* Focusing Point* Makro* AF-assist Light* AF Operation* Zoom*

Flash* Flash Quality* White Balance* Exposure Compensation* Flash Exposure Compensation* Metering Mode* ISO Speed* Photo Effect* Tv/Av Setting* Av* Tv*

*(Software Settings for “Canon RemoteCapture”)

Zeiss Axioplan 8 none

2nd to last marking Air (no oil objectives)

Canon PowerShot A70 5.4 - 16.2mm Large/Super Fine - 2048x1536 ( 1 MB) 0 degree Automatic Selection Off Off AF Lock 1.3x to 3.2x (also further enhanced electronically)

Nicols //Nicols +

Off/ Off /

Fluorescent0 Fluorescent 0

/Evaluative / Evaluative

50Vivid 50 Vivid

Manual8.0 Manual 8.0

1/250 to 1/20001/3 to 1/50

Preface

Having been involved with ore microscopy for many years, I came to the conclusion that the magnificent work by Ramdohr (1969) on ore petrography needed to be supplemented by colour photos for as many different ore minerals as possible. It is simply impossible to deduce colour tints from black and white micrographs or descriptions alone (not to mention the many ill-tinted micrographs found on the internet). This task was quite daunting, because of the large number of minerals to be photographed. However, tools that were not accessible to Ramdohr, i.e., a desktop computer connected to a digital camera that was mounted on the microscope, eased the challenge considerably.

This atlas does not attempt to be a handbook on how to examine ore minerals under the microscope (see following paragraph for some of the respective literature) or distinguish textures for obtaining genetic information, but rather it is meant as a search file for comparative use. Therefore, all text is limited to a minimum. This seems to be contradicted by the fact that the tables relating to an individual mineral are repeated for other members of the same group. Nevertheless, in order to show all relevant information close to the particular photo plate without the need to further search for comprehensive data tabulations, I adopted this approach.

Ore minerals generally don’t occur just by themselves and, thus, a number of common gangue minerals are incorporated in this book, together with secondary alteration minerals. The latter present a further tool for the identification of entire mineral associations, because various elements exhibit very typical colours in their oxidised states. Examples are copper phases with green, blue, and sometimes red tinges or cobalt with pink shades, while iron shows pronounced tones of red, brown, and occasionally green. The term gangue minerals can also be fairly misleading for several reasons: a) it constitutes a more economic approach than a strict scientific meaning - a particular gangue mineral may be considered as waste in one deposit and as ore mineral in another (e.g., hedenbergite), b) its meaning shifts over time - sphalerite, for instance, was dumped by early miners, while it is being mined today.

Strunz (2001) provides the mineralogical frame in which the minerals of this book are arranged and presented. This grouping of interrelated compounds also makes sense with respect to optical characteristics because of distinctive similarities within the respective groups. Such semblance also proves to be a valuable tool in the identification of unknown minerals.

Other books on ore microscopy, which were used during the preparation phase for this atlas, are Baumann and Leeder (1991), Craig and Vaughan (1981), Gierth (1989), Mücke (1989), and Oelsner (1960), while Criddle and Stanley (1986) and Rösler (1991) were frequently consulted for optical and mineralogical information, respectively. Further helpful publications on mineralogy and geochemistry were by Harris and Burke (1970), Lawrence (1998), Makeyev et. al. (1999), Mücke et al. (1999), Naldrett (2005), Strunz et al. (1958).

The literature pertaining to the investigated mineral deposits is tremendous and it would have been superfluous to list it comprehensively. However, the most important publications for this atlas are the following ones (excluding those already mentioned above): Barnes and Hay (1983), Blatter (1997), Boström et al. (1979), Cabri and Laflamme (1997), Cairncross (2004), Cook (1979), Dobrovolskaya (1999), Dunn (1995), Dyuzhikov et al. (1999), Excursion-Participants (2002), Favreau and Dietrich (2006), Flach (1984), Garuti et al. (1995), Graeme (1981), Graeme (1993), Graeser (1965), Grokhovskaya (1999), Hammer and Peterson (1968), Hernandez et al. (1999), Holtstam and Langhof (1999), Jahn (1991), Keller (1984), Lahl (2005), Leydet (2006), Lhoest (1995), Lombaard (1986), Martin et al. (1994), Nysten et al. (1999), Ondruš et al. (1997), Parafiniuk and Domanska (2002), Pauliš and Haake (1991), Pawlowski (1991), Ream (2004), Rieck (1993), Sejkora and Tvrdý (2002), Shiga (1987), Sokatsch and Weiss (2001), Stahle et al. (2002), Stekhin (1994), Strunz et al. (1958), Szentpéteri et al. (1999), Torgashin (1994), Torres-Ruiz et al. (1996), Walenta (1992), Watanabe (1959), Watanabe et al. (1960), Watkinson (1999), Weiß (1990), Whitehead (1919), Wilson (1950a, b), Wittern (2001).

A fast internet access helped to obtain additional information, whenever necessary. An enormous wealth of data regarding mineral associations from world-wide locations was found at mindat.org - an exquisite source of information, particularly in cases when rare samples were examined for which there was no proper mineral inventory. Further deposit descriptions originated from: binn.strahlen.org, franklin-sterlinghill.com, ber gbauverein-ronneburg.de, ge-at.iastate.edu, geology.neab.net/locality/lainejau.htm, grube-lengenbach.ch, k1q.net, metalin.com, nrm.se, vstm.at, wsu.edu, outokumpu.fi, zinngrube.de. These were supplemented by data from gl.rhbnc.ac.uk/geode.

Comparable to mindat.org, webmineral.com provides a vast amount of detailed mineralogical, geochemical, and optical data; specific mineral descriptions derived from un2sg4.unige.ch/athena, miner.ch, rruff.geo.arizona.edu, duke.edu, gov.mb.ca, as well as from various museums assembled at euromin.w3sites.net (for precise links see “Bibliography/Electronic Media” on page 870).

Mineral Descriptions

1 Goethite lining vug in coronadite, Broken Hill, Australia

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Explanations & Abbreviations

Mineral Name Synonyms

Geologic Environment Reflection Colour

Internal Reflections

The mineral names reflect the naming of by the International Mineralogical Association (IMA), wherever possible, and are printed in bold in the index section. Synonyms (and outdated names) are provided in brackets immediately behind the mineral name, they are printed in italics in the index section. Typical geological settings are presented for each mineral, although in many cases, these do not cover all possible genetic conditions. This is the mineral’s colour in reflected light (without polarisers) as observed on an untarnished surface; it occasionally differs from the handspecimen, which may show internal reflections that contribute to the overall colour impression (even for ore minerals, this is sometimes the case under the microscope). Cleavage and cracks in the observed mineral or phase boundaries between adjacent minerals can result in reflections within semi-transparent or translucent minerals. Reflectance

Bireflectance Anisotropy

Pleochroism

Reflectance relates to the percentage of light that is reflected from the mineral’s surface relative to the initial beam. Literature data were recalculated to 589 nm for direct comparison of all data (observation wave lengths vary considerably from one publication to the next). When minimum - maximum values are provided, they show the range found for different optical axes in cases of optical anisotropic. Values without decimal places and in square brackets (e.g., [35]) are visual estimates on the basis of photo comparisons (i.e., taken with the same camera setting) and reflection data of 6 well-known minerals; wherever possible, these estimates were made with minerals of similar tints. Tests showed errors ranging between 2 and 5 percent points (e.g. 38% instead of the documented 35%); occasionally, this error may be larger (in particular within fine-grained materials). Bireflectance is an optical effect (see also pleochroism), where the reflectance changes when the sample is rotated while illuminated by plane polarised light. The polarisers are not crossed (preferably the polariser is taken out) to observe bireflectance. Isotropic minerals, such as pyrite or galena, do not show bireflectance. Anisotropic minerals possess differences in physical properties (e.g., hardness, refractive index, density, etc.) along different crystallographic axes. Here, anisotropy either results in different grey shades or colours, when the sample is rotated and observed under crossed nicols (polariser + analyser). Occasionally, it is necessary to slightly open the analyser in order to judge anisotropy. Isotropic minerals, such as pyrite or galena, generally do not show anisotropy (although some exceptions are known and also documented in this atlas: see galena, for instance). Pleochroism describes a mineral’s ability to absorb/reflect light of different wavelengths depending on the crystallographic orientation of the sample. This results in a colour change when the specimen is rotated (under parallel nicols). Pleochroism is the general term that includes dichroism in uniaxial (one optical axis) and trichroism in biaxial (two optical axes) crystals. I/A.01-10

Hermann-Maugin Symbols for Crystallographic Classes

[a - o] Nic. //, Nic.+

These are the Strunz classification symbols for the respective mineral.

Wherever a precise Hermann-Maugin symbol for the respective mineral has not yet been determined, the class is given as stated below: tri. = triclinic trig. = trigonal mono. = monoclinic ortho. = orthorhombic tet. = tetragonal hex. = hexagonal cub. = cubic (isometric) The letters correspond to individuals and/or institutions providing polished sections for examination and presentation (referenced on page XV). The nicols (polariser & analyser) are parallel (//) or crossed (+, exact alignment). However, in reflected light microscopy, the analyser is occasionally rotated a few degrees (denoted as (+2°) from its ideal position to emphasise anisotropy effects.

Descriptions A

Skeletal copper (light pink) with small specs of cuprite (bluish grey); Broken Hill, Australia [c]; Nic. // Anhedral native copper (pink tint) next to domeykite (grey) in jasper; Çayeli, NE Turkey [n]; Nic. // Anhedral native copper (dark; scratches) next to domeykite (almost black) in jasper (red internal reflections); Çayeli, NE Turkey [n]; Nic. +

Copper (Cuivre, Kupfer)

Geologic Environment:basic Precambrian magmatites, at border between oxidation and cementation zone, cap rocks of Cu sulfide veins, volcanic and sedimentary rocks

Reflection Colour:Internal Reflections: pink-white

Reflectance [%]: Anisotropy: Pleochroism: 92.20isotropic Bireflectance:

Strunz Classification - Group Members - Chemical Formula - Crystallography

I/A.01-Copper, Silver and Gold Series

I/A.01-10 Copper Cu 4/m 3– 2/m

I/A.01-15 Allabogdanite (Fe,Ni)2P 2/m 2/m 2/m

I/A.01-20 Silver Ag 4/m 3– 2/m

I/A.01-40 Gold Au 4/m 3– 2/m

I/A.01-50 Auricupride Cu3Au 4/m 3– 2/m

I/A.01-60 Tetraauricupride AuCu 4/m 2/m 2/m

I/A.01-65 Bogdanovite (Au,Te,Pb)3(Cu,Fe) 4/m 3– 2/m

I/A.01-68 Hunchunite (Au,Ag)2Pb 4/m 3– 2/m

I/A.01-70AnyuiiteAu(Pb,Sb)24/m 2/m 2/m

Copper

B C 125 μ125 μ

Descriptions A

Anhedral silver (white) in galena (light grey), thin reaction rim of argentite (greenish grey); Monte Narba, Sardinia, Italy [b]; Nic. // Anhedral silver (medium grey, many scratches) in galena (dark, some scratches); Monte Narba, Sardinia, Italy [b]; Nic. + Myrmekitic intergrowth of native silver (white), chalcopyrite (olive), and cabriite (pinkish cream, slight bireflectance), niggliite (here greenish cream), geversite (blue grey), galena (medium grey); Oktjabrsky, Norilsk, GUS [d]; Nic. // Fine-grained aggregates of “knitted” silver (white), galena (medium grey), carbonate matrix (dark grey); Brand-Erbisdorf, Saxony, Germany [g]; Nic. // Silver (isotropic), galena (isotropic), carbonates (white and brownish internal reflections); Brand-Erbisdorf, Saxony, Germany [g]; Nic. +

Silver

Geologic Environment:hydrothermal sulfide veins

Reflection Colour:Internal Reflections: bright silver white

Reflectance [%]:

Anisotropy: Pleochroism:

82.82 (87.5 antimonian) isotropic, scratches give impression of anisotropy

Bireflectance:

(Parte 2 de 3)

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