1993 1

Introduction to Ore Microscopy I

Erich U. Petersen

OBJECTIVE

In this laboratory exercise you will learn to use reflected-light observations toidentify minerals in polished mounts or polished thin-sections.

PROCEDURE

Read Craig and Vaughan (1981), Spry and Gedlinske (1987), and review theaccompanying summary before you begin work. Eight techniques will be used todistinguish minerals in reflected-light.

1. Color - especially color contrasts between your unknown and known minerals.Best seen in oil, but it's messy (We will not use oils).

2. Reflectivity - the amount of light reflected back by the mineral. In a lab set up forquantitative work, monochromatic light sources are used, and the light reflectedfrom the mineral is measured by a photocell. We will simply note whether thereflectivity is weak, moderate, or strong.

3. Hardness - In a lab set up for quantitative work, the size of indentations made bysmall weights dropped for a fixed distance onto the polished surface are comparedfrom mineral to mineral (Microhardness testing). Instead, we will observe themovement of the pseudo-Becke line, a faint bright line which moves into the softerof two adjacent minerals as the objective/sample distance is increased.

4. Texture of the polished surface is often diagnostic. For example, intersectingorthogonal cleavages in galena give rise to prominent triangular pits. In addition,noting whether the mineral tends to form euhedral crystals or is anhedral is veryuseful.

5. Bireflectance - an optical effect similar to pleochroism - the mineral changes color asit is rotated in plane polarized light (polarizers not crossed).

6. Anisotropy - a change in color observed with cross-polarized light. Weakanisotropy (which is quite common) is best observed with the polarizers, almost,but not quite, crossed.

7. Internal reflections are apparent in some incompletely opaque minerals.

8. Mineral associations are extremely useful. For example sphalerite commonlyoccurs with galena.

1998 EUP7

THE OPTICAL PROPERTIES OF ORE MINERALS(A Primmer)

The optical properties of ore minerals determinable in polarized reflected light fallnaturally into two groups:

1. Properties observed without the analyzer: color, reflectivity, relative hardness, kalbhardness, bireflectance, morphological character and pleochroism.

2. Properties observed between crossed nicols: anisotropism vs. isotropism,polarization colors, rotation properties, dispersion colors, morphological characterand internal reflections.

This handout describes these various optical properties and the procedures used toobserve them. For a theoretical explanation of these phenomena, the reader is referred tothe contributions of Cameron (1961) and Freund (1967).

A. Relative Reflectivity and Color

In reflected light there is no optical path in the specimen and hence there is nointerference. The phenomena observed are due to surface reflection, and the most strikingis the reflectivity, which varies from below 10 to nearly 100 percent in opaque substances.Reflectivity is defined as the ratio of the intensity of the light reflected by a mineral to theintensity of the light incident upon it, expressed in percent. The qualitative degree ofreflectivity is judged in comparison with a known mineral. It must be considered that thevisual impression of the reflectivity is influenced markedly by the effect of contrast toneighboring crystals with higher or lower reflectivity. In an environment of highlyreflecting crystals, a moderately reflecting crystal appears oppressed and pale or,conversely, will seem brighter than would correspond to its real reflectivity. For example,consider a polished specimen of quartzose gangue with molybdenite (R percent 20.9-40.0)and arsenopyrite (R percent to 52.0). The molybdenite appears bright against the gangue,but when there is arsenopyrite in the field, the molybdenite is so dull that it hardly appearsto be the same mineral as before. In such cases, use of the incident field stop (IFS) may beof assistance in ascertaining relative reflectivity of ore minerals. Remember that thebrightest crystal present in the field of vision determines the impression of brightness of theothers.

Estimation by eye can rapidly establish an order of reflectivity in the ore minerals ina specimen, but a difference in color can affect this subjective judgment. For example,niccolite is pinkish-yellow and has a range of 52 to 58 percent reflectivity in white light.Cobaltite is pinkish white and in the same light has a reflectivity of 52.7 percent, yet itgenerally appears distinctly the brighter of the two. Even in well-polished sectionsminerals vary in the way that they take the polish. If one mineral takes a less good polishthan another of similar reflectivity, then the first mineral will appear distinctly less highlyreflecting than the second.

Assuming equally good polish, isometric minerals exhibit constant reflectivitywithin a given species - all galena, regardless of the orientation of the crystal with respect tothe plane of the polish, has the same silvery-white appearance in vertically reflected light.Non-isometric minerals theoretically have different absorption coefficients, hence differentreflectivities, in different optical directions. In a few minerals, such as covellite andmolybdenite, such differences are readily recognizable to the unaided eye, and a givenspecies, e.g. chalcopyrite, shows essentially the same reflectivity regardless of orientation.

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Dissolved impurities also affect reflectivity, but again, except in a few cases likesphalerite where an increase in iron content increases reflectivity, the differences arepractically negligible as far as visual comparison is concerned.

B. Color of Reflection

The colors of ore minerals, which range from pure white to gray, are one of theirmost characteristic and useful properties. The eye is poor at 'remembering' a particularcolor after even a very short time lag, and hence consecutive comparisons of color can bemade only for large differences. This means that a color cannot be distinguished by aname, except in a crude way. For example pyrrhotite has a characteristic color ('pyrrhotitecolor') which the observer soon learns to recognize, but which has been described in theliterature as cream, pale brownish-cream, clear-bronze, pale yellowish-red, and so on. Ascolor is a function of the character of the human eye, each observer must make his owndescriptions of the colors of minerals and must not be disconcerted if the pale creammineral he has just observed is described as light yellow by someone else. As the eye isquite sensitive to very slight differences in hue or brightness of two minerals lying side byside, use of the double, or comparison microscope is strongly urged. This apparatusallows an unknown mineral to be viewed in the same field with a standard mineral fromanother specimen.

Notes:

1. A difference in reflectivity can affect the eye, and where two minerals have a similarcolor but different reflectivity, the one of higher reflectivity appears the clearerbecause of its greater brightness.

2. The color of a mineral is strongly influenced by the color of neighboring crystals('mutual color interference'). For example, chalcopyrite by itself has acharacteristic and easily recognizable yellow color. Inside sphalerite, it appears avery clear yellow, but in contrast with native gold, it appears a dull greenishyellow. In these circumstances, it may help to close down the IFS, so that the fieldof view is essentially monomineralic.

3. Color is a function of the index of refraction of the immersion medium (the mediumcomprising the space between the objective and the surface of the mineral).Covellite in air (R.I. = 1.00) is deep blue, in water (R.I. - 1.333) violet blue, incedar oil (1.515) red violet, and in methelene iodide (R.I. = 1.74) orange red.

4. It should be stressed that many minerals which occupy solid solution fields (forexample ilmenite, sphalerite, pentlandite) will exhibit color variations, even inidentically oriented sections; occasionally, this leads to an overlapping of the colorsof minerals which may normally distinguished readily.

In some cases the change of color produced by immersion in cedar oil is an aid toidentification.

TO OBSERVE COLOR:

IFS and IAD (incident aperture diaphram) opened wideLow power objectiveHigh voltage for light of good intensityPolarizer inserted, Analyzer withdrawn

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C. Bireflectance and Pleochroism

Isometric minerals (for example, pyrite, galena, pentlandite) remain unchanged incolor and brightness as the stage of the microscope is turned. Many minerals of the othercrystal systems, however, show distinct changes in brightness or color, or both, withrotation of the stage, and grains of differing orientation side by side in a section differ incolor or brightness. The effects are analogous in appearance to absorption, dichroism andpleochroism shown by transparent minerals in thin section, and in the literature of oremicroscopy are commonly referred to as pleochroism or reflection pleochroism .

Bireflectance or bireflexion is the change in intensity of the light reflected from amineral as it is rotated on the microscope stage.

Reflection pleochroism is the variation in tint of a colored mineral observed as it isrotated on the microscope stage. A pleochroic mineral is by necessity alsobireflectant.

The change of tint may make it difficult to be certain of change in intensity, if this isslight. These two phenomena are manifestations of anisotropy in the mineral section. Thebireflectance depends on the difference between the two reflectivities (O and E) whereas thepleochroism depends on the differences between the dispersions of the two reflectivities. Itmust be remembered that for a given mineral, the intensity of the bireflectance varies withthe orientation of the section and that the highest bireflectance observed for the mineral in apolished section is not necessarily the maximum for the mineral. For example, only avertical section of a uniaxial mineral (//C) will show the maximum bireflectance for themineral in question. For all practical purposes, four degrees of intensity can bedistinguished:

1. Bireflectance strong:graphite, molybdenite, pyrolusite, covellite, marcasite, stibnite

2. Bireflectance medium:ilmenite, pyrrhotite, niccolite, cubanite

3. Bireflectance weak:arsenopyrite, enargite, hematite, loellingite (Best observed by contrastagainst neighboring isotropic crystals)

4. Bireflectance weak to absent:chalcocite, argentite, chalcopyrite

In white light, weak bireflectance is much more easily observed if accompanied inthe mineral by even a slight reflection pleochroism, since the eye is much more sensitive tochange of tint than to change of intensity. Thus, with minerals showing dispersion of thebireflectance sufficient to alter the color perceived by the eye (i.e. the mineral ispleochroic), the detection of even very weak bireflectance is difficult. In reflectionpleochroism usually the dominant color does not change, only the tints and intensities;these changes are, however, very useful in diagnosis. Some examples are given below:

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Examples of Reflection Pleochroism

Mineral Mean Color Color of R1 (darker) Color of R2 (lighter)

covellite blue deep violet blue bluish-white

molybdenite whitish to gray whitish-gray white

pyrrhotite clear brownish yellow pinkish-brown brownish-yellow

niccolite pinkish to brownish whiteclear pinkish-brown bluish-white

cubanite bronze-yellow pink-brown clear yellow

Notes:

1. Bireflectance, like color, is a function of the index of refraction of the immersionmedium. Generally, the higher the index of refraction of the immersion medium,the higher the bireflectance of an ore mineral. You should examine covellite both inair and in cedar oil to convince yourself of this fact.

2. Bireflectance is also a function of crystallographic orientation, and for everyanisotropic mineral, there is at least one crystallographic plane, sections parallel towhich will show no bireflectance (for example, sections of hexagonal or tetragonalcrystals perpendicular to the c-axis). Thus, observations of bireflectance should bemade on several grains of each anisotropic silicates.

3. Bireflectance is also shown by the carbonate of Pb, Fe, Mg and Ca, but not by thecommon rock-forming silicates.

4. When studying a section, always record the strength of the bireflectance, and alsoany color changes, if detectable, for several grains of each bireflectant mineral,noting the relationships between the positions of maximum and minimumreflectance and crystal outline, cleavage traces, etc.

TO OBSERVE BIREFLECTANCE (AND PLEOCHROISM):

IFS and IAD opened widePolarizer inserted, analyzer withdrawnLow power objectiveHigh voltageChoose an area with several grains of the mineral in question and NO grainsof any other mineral showing bireflectance. (If this is not possible, closedown the IFS to shut out the unwanted mineral grains from the field ofview).

One final note . . . when you can detect the bireflectance of pyrrhotite andarsenopyrite your eye is trained to a satisfactory sensitivity. Congratulations.

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D. Measurement of Hardness

There are numerous ways of estimating hardness in polished surfaces. When aspecimen is polished on a yielding (e.g. cloth) lap, obviously the harder minerals will becut less than the softer and thus stand in positive relief with respect to the softer. In suchcases it is possible to judge the relative polishing hardness by mere observation. But if thespecimen has a low-relief polish from a hard lap and diamond dust the hardness of mineralssofter than a steel needle may be judged by drawing the needle lightly across the surface ofthe mineral in question. The lightest possible scratch is the most definitive. Comparativehardness can be ascertained by drawing the needle lightly across a contact between aknown-mineral and an unknown, and relative hardness can be obtained by varying thespecimen - objective distance. With a little practice it is possible to estimate the difficultywith which soft minerals scratch. One should eventually be able to estimate which ofShort's soft mineral groups A, B, C and D applies. With increasing practice, one can addqualifications such as A-, slightly softer than A. This is an important property to measureas accurately as possible.

Kalb Hardness Determination

At the junction of a hard and softgrain, there tends to be a slight departurefrom flatness, and the Kalb light-line effect,which is analogous to the Becke-line effect,can be observed.

As the distance between the objectivelens and the polished section is increased (i.e.the stage is lowered) the white line will moveinto the softer mineral.

TO OBSERVE THE KALB LINE:

Moderate voltage Formation of the Kalb line at the junctionIFS opened wide of a hard mineral (M1) and a softIAD closed mineral (M2).10 X or 40 X power objective Polarizer inserted, analyzer withdrawn

E. Anisotropy and Polarization Colors

To observe these phenomena, both the analyzer and polarizer must be crossed .When the stage is rotated with the polars crossed, it is noticeable that certain ore grainsremain dark; these are referred to as uniradial sections (mono-reflecting) and are eitherisometric minerals or else basal sections of some uniaxial mineral. These basal sections canbe recognized as such because different sections of the same mineral are bireflecting.Sometimes the section, although uniradial, is not completely dark; this is the case withminerals of high (metallic) reflectivity. But such sections can be recognized as beinguniradial because the slight luminosity remains constant on rotation of the stage; this can bemore easily observed if the polarizer is uncrossed very slightly (2 or 3o). Thus, undercrossed polars, an isotropic mineral will show one of two kinds of behavior:

1998 EUP12

1. It will remain completely dark through 360o of rotation. Examples of isotropicminerals with good extinction (i.e. low to medium reflectivity) are sphalerite,magnetic and chromite.

2. It will be very faintly illuminated, but will show no change in color or intensity ofillumination through 360o of rotation. Isotropic minerals with poor extinction (i.e.of high reflectivity) are pyrite and native silver.

One precaution must be kept in mind, however. Not all isometric minerals are fullyisotropic. Pyrite and bornite, for example, are often anisotropic, although many X-raystudies have shown that pyrite at least is invariably isometric. Anomalous anisotropism isvery weak, however, and it rarely hinders identification.

Under crossed polars an anisotropic mineral will show a change in intensity ofillumination or color of illumination, or both, as the stage is rotated. The observed colorsare referred to as polarization colors and are often highly characteristic and useful in mineralidentification. If the nicols are exactly crossed, then in general in a 360o rotation of thestage there will be four positions of maximum darkness ('extinction positions') 90o apartalternating with four positions of maximum illumination lying at about 45o to the positionsof darkness. Examples of distinctly anisotropic minerals (i.e. with distinct positions ofextinction or minimum luminosity on rotation of the stage) are pyrrhotite, wolframite andarsenopyrite. Strongly anisotropic minerals, which have bright reflection in between thefour definite positions of extinction (or minimum illumination) include graphite, covellite,sylvanite and chalcophenite. Weakly anisotropic minerals such as chalcopyrite should beviewed very carefully in strong light. In many cases it is best to view adjacent grains whilerotating the stage of the microscope, rather than try to see light and dark positions in asingle grain. Remember that polarization colors are constant only if the nicols are exactlycrossed.

Care must be taken in using anisotropy not to confuse reflection from scratches orroughness of polish for a true anisotropic. Poorly polished pyrite often shows apparentanisotropy which will disappear if the polish is improved. It must also be remembered thatany anisotropic mineral may show an isotropic section by fortuitous orientation. More thanone grain must be observed before concluding that a mineral is isotropic.

Some anisotropic minerals show a distinct and characteristic sequence of colors asthe polarizer is turned, degree by degree, to and beyond the minimum position. Thesection is turned in white light between crossed polars, so that the vibration direction ofgreater reflectivity is parallel to the vibration direction of the polarizer (N S). The stage isthen turned first clockwise to the plus 45o position. In each of these two positions thepolarizer is slowly turned through a few degrees, and the sequence of tints is noted. Twoexamples are shown below; in the last column, mention is made only of the tints whichdiffer in the two stage settings:

Tints at 45o setting Rotation of Tints at 45o settingMineral of stage polarizer of stage

niccolite Blue 0oDeep blue -1oDark violet gray -2oDeep brownish-yellow -4o

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Clear orange-brown -5o Bluish-white to clear blue

cubanite Bluish-gray 0oDeep violet -2oReddish brick-brown -5o to -4o Bluish-grayLeather-brown -6o to -5o yellowish-whitePurplish -6o

TO OBSERVE ANISOTROPY/POLARIZATION COLORS:

Polarizer and analyzer insertedIntense illuminationLow power objective (10X)IFS may be closed down to cut out periphery of field

F. Recognition of Internal Reflections

Many ore specimens (for example, sphalerite) are sufficiently translucent ortransparent to admit incident light to substantial depths below the surface of the specimen.If this light is reflected back up through the tube of the microscope by a cleavage crack,grain boundary, or some other subsurface feature, it will assume the color of the mineral intransmitted light. Thus, malachite has green internal reflections, but the true surfacereflection color is dark-gray. Cuprite has scarlet red internal reflections, but the truesurface color is bluish-white.

After focusing the specimen in reflected light, turn off the vertically incident lightand view the surface in a strong beam of obliquely incident light. Scratches on the polishedsurface will appear bright, but if the focus is lowered slightly, internal reflections may beobserved. Table 2 (Short, p. 293) lists minerals with distinctive internal reflections. Non-opaque minerals, for example, quartz and the feldspars, will also show internal reflections -- usually white or perhaps yellow in the case of biotite.

Most internal reflections are in the range from red to brown to yellow. Someexperience is required for distinguishing the color of internal reflections of differentminerals in the above color range. Consequently, it is mostly not the color of internalreflections of different minerals that is useful in the determination of minerals, but rather thepresence or absence of internal reflections, and, where present, their frequency andintensity. Some examples are listed below:

Visibility of Internal Reflection Mineral Colors of Internal Reflection

Often visible in air scheelite white and intense in oilsphalerite yellow to reddish-brown

cinnabar clear blood redmiargyrite deep raspberry redrutile clear yellow to deep brown

azurite bluecuprite strong red

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Sometimes visible in air chromite brownish-redand often in oil hematite blood red

wolframite deep brownilmenite very deep brown

Not usually visible in air tetrahedrite reddish brownand only rarely in oil uraninite very deep brown

Variations in composition affect the abundance of internal reflections. Internalreflections are usually numerous in sphalerite low in iron, and few or lacking in sphaleriterich in iron or containing minute inclusions of chalcopyrite or pyrrhotite.

TO OBSERVE INTERNAL REFLECTIONS:

IAD openedIFS opened or closed downNicols crossed 40X or 10X objectiveCedar oil immersion (R.I. = 1.515) strongly recommended for use with 100XobjectiveLarge grains generally show internal reflections best

It is hoped that these summary notes will be useful in giving you an appreciation ofsome of the important optical techniques available for the identification of ore minerals.The only way to become proficient in this art is through continued, diligent practice, and sothe ball is now in your court . . . . .

F2F1

M2 M1

Focus initially atF1; Lower mineralspecimen so that thefocus is now at F2and observe th Kalbline.

Formationof the Kalb Line at thejunction of a hard mineral (M1) anda soft mineral (M1).

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Reflected Light Properties of Some Ore Minerals

argentite Ag2S Isometric/Monoclinic H = 2-2.5Gray to greenish

darker than galena; greener than silverLow reflectivityIsotropic to weakly anisotropic

arsenopyrite FeAsS Monoclinic H = 5.5-6White or cream to pink - pleochroic

whiter than pyrite; grayer than antimonyyellow relative to sphalerite and galena

High reflectivityAnisotropic - strongly blue to green to brown

bismuth (native) Bi Hexagonal H = 2-2.5White tarnishing to pink and brown

brighter than antimony; whiter than niccolitePleochroicVery high reflectivityAnisotropic - distinct to strongly so

bornite Cu5FeS4 Isometric H = 3Pinkish brown to orange - tarnishes purple and violet; darker

and more variegated than enargiteModerate reflectivityAnisotropic - weakly anomalous (it's isometric)

cassiterite SnO2 Tetragonal H = 6-7Gray - weakly pleochroic

darker than sphalerite and wolframiteLow reflectivityAnisotropic - distinctly so

chalcocite Cu2S Orthorhombic H = 2.5-3Bluish white - weekly pleochroic

bluish relative to galenabluish-gray relative to pyritewhite relative to covellite, covellite looks pinkbluish relative to tetrahedrite

Moderate reflectivityAnisotropic - weak to distinct; emerald green to pinkish

chalcopyrite CuFeS2 Tetragonal H = 3.5-4Brassy yellow but tarnishes - weakly pleochroic

darker and yellower than pyrite and galenalighter than pyrrhotitebright yellow relative to sphalerite andmagnetite and relative to tetrahedrite and stannite

High reflectivityAnisotropic - weak; gray blue to greenish yellow

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covellite CuS Hexagonal H = 1.5-2Indigo blue to bluish white strongly pleochroic

pinkish and lighter relative to chalcociteModerate reflectivityExtremely anisotropic: fiery orange to reddish brown

chromite FeCr2O4 Isometric H = 5.5Dark gray with brownish tint

darker than magnetitedarker and red brown relative to ilmenitesimilar to sphalerite but slightly darker

Low reflectivityIsotropic

enargite Cu3AsS4 Orthorhombic H = 3Grayish pink to grayish violet - pleochroic

pinkish white relative to bornitepinkish brown relative to chalcocitegray relative to galenadarker pink than tennantite

Moderate reflectivityAnisotropic - strong blue to red to orange

galena PbS Isometric H = 2.5Bright white

whiter than sphalerite and stibnitepinker than tennantite

Prominent triangular pitsHigh reflectivityIsotropic

hematite Fe2O3 Hexagonal H = 5.5-6.5Gray-white with bluish tint - weakly pleochroic

whiter than ilmenite magnetite and goethitebluish gray relative to pyriteslightly brown relative to chalcocitewhite relative to cuprite

Moderate to high reflectivityDistinctly anisotropic - gray-blue to gray-yellow

huebnerite MnWO4 Monoclinic H = 5Gray - pleochroic

similar to sphaleritereddish and lighter than wolframite

Low reflectivityAnisotropic - strong

ilmenite FeTiO3 Hexagonal H = 5.5-6Pleochroic - Light to dark brown + pink or violet tints

darker than magnetite, much darker than hematitebrighter and brown relative to sphaleritelighter and red brown relative to chromite

Low reflectivityAnisotropic - strong - green gray to brown gray

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magnetite Fe3O4 Isometric H = 6Gray often with a brown tint

admixed TiO2 gives a brown tintadmixed MnO gives a yellow-green tintmuch darker and browner than hematitelighter than ilmenitelighter than sphaleritedarker and duller than psilomelane

Low reflectivityIsotropic

marcasite FeS2 Orthorhombic H = 6-6.5Yellowish white with pink green or yellow tintsPleochroic white to yellow whiter than pyriteHigh reflectivityAnisotropic - strong: blue-yellow-gray

NiS Hexagonal H = 3-3.5Yellow

lighter than chalcopyrite; chalcopyrite appears greenyellower than pentlandite; no brown tints

Pleochroic bright to brownish yellowHigh reflectivityAnisotropic - brown to blue gray - strong

molybdenite MoS2 Hexagonal H = 1-1.5White to dull gray with dark blue tint -

very similar to galenamuch lighter than graphite

PleochroicBasal sections appear isotropicReflectivity - varies with orientationAnisotropic - strongly - white with a pink tint

niccolite NiAs Hexagonal H = 5-5.5Yellow pink to brown pink - strongly pleochroic

pinker than bismuthlighter and pinker than pyrrhotitemuch lighter than bornite

Very high reflectivityAnisotropic - strongly yellow to gray-green to violet blue

pentlandite (Fe,Ni)9S8 Isometric H = 3.5-4Light cream or yellowish

much lighter than pyrrhotite which appears brownHigh reflectivityIsotropic - but no complete extinction

pyrrhotite Fe1-XS Hexagonal H = 4.Cream to red brown-tarnishes-pleochroic

much darker than pentlandite and niccolitecream-brown relative to bismuth

High reflectivityAnisotropic - strong-yellow-gray to green-gray to blue gray

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pyrite FeS2 Isometric H = 6-6.5Yellowish white

yellower than marcasite, arsenopyrite, and galenaless yellow than chalcopyritegray-green relative to silver

High reflectivityIsotropic

rutile TiO2 Tetragonal H =High reflectivityAnisotropicInternal reflections, Twinning common

silver (native) Ag Isometric H = 2.5-3Bright white - tarnishes to pink or brown

brighter than native antimony, copper, or bismuthReflectivity - the highest of all ore minerals

sphalerite ZnS Isometric H = 3.5-4Gray - darker than magnetiteOften displays internal reflectionsLow reflectivityIsotropic

stannite Cu2FeSnS4 Isometric/Tetragonal H=3.5Brownish olive green - variable pleochroic

darker than tetrahedritelighter than sphaleritedark and green brown relative to chalcopyrite

Moderate reflectivityAnisotropic - strongly yellow brown to olive to bluish

wolframite ( Fe , Mn)WO4 Monoclinic H = 5-5.5Gray to white

similar to sphalerite and magnetiteLow reflectivityAnisotropic strongly

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REFERENCES

Craig, J.R. and Vaughan, D.J., 1981, Ore Microscopy and Ore Petrography . Wiley,New York, 1-14, 33-47, 315-377.

Klein, C. and Hurlbut, C.S., Jr., Manual of Mineralogy, (Any Edition), John Wiley andSons.

Palache, C., Berman, H. and Frondel, C., 1944, Dana's System of Mineralogy, Volume I,(Seventh edition), John Wiley and Sons, 834 p.

Spry, P.G. and Gedlinske, B.L., 1987, Tables for the Determination of Common Opaque Minerals . Economic Geology.

Wuensch, B.J., 1974, Sulfide crystal chemistry, Sulfide Mineralogy , (P.H. Ribbe, Ed.),W21- W44.

Zoltai, T. and Stout, J.H., 1984, Mineralogy: Concepts and Principles , BurgessPublishing Company.

Mineral Identification Tree

Color

Pleochroism(1 filter)

Anisotopism(2 filters)

Internal Reflections

Hardness

Colored Weakly Colored

S W SW

S W SM

P AP A

Mineral Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

M

S HM S HM S HM S HM

W

P A P A

Pleochroism, Anisotropism:W, weakS, strong

Internal Refelctions:A, absentP, present

Hardness:S, soft

M, mediumH, hard

Mineral Group

1 breithauptitecovellitedelafossitefamatiniteidaiteluzonitemackinawitemarcasitemawsoniteniccolitevalleriite

2 cubaniteenargitemilleriteniccolitepyrrhotite

3 bornitechalcocitechalcopyritebornite

4 bornitebravoitechalcopyritecopperdigenitegold/electrumpyritetetrahedrite-tennantiteulvospinel

5 alabanditeamphibolebiotitebranneritechromitecolumbitecupritefeldsparfranklinitefreibergite

garnetjacobsitepyroxenequartzsphaleritetetrahedrite-tennatiteuraninitewurtzitezincite

6 calaveritechalcocitedjurleitefreibergitegalenasilvertetradymite

7 allargentumcarrolitecoffinitecooperitemaghemitemaucheritepentlanditeplatinumtetrahedrite-tennantite

8 bixbyitebraunitecarrolitechromitecobaltitegersdorffitejacobsitelinnaeitemagnetitepyriteseigeniteskutteruditesperryliteullmannite

violarite

9 pearciterealgar

10cupritescheelitezincite

11cassiteritecolumbitegoethitehematitewolframite

12acanthiteargentitestephanitetetradymite

13bournonitechalcostibitedyscrasitegaucodot

14braunitecobaltite

15cassiteritecinnabarcupritegoethitehausmannitehematitemanganitepearceite-polybasiterealgarrutilezincite

16bismuthbismuthiniteboulangerite

bournonitekrenneritestromeyeritetetradymite

17antimonyarsenicbraggitecubaniteenargiteparar-ammelsbergitestannite

18arsenopyriteilmeniteloellingitepyrolusiterammelsberitesafflorite

19cnnabarjamesonitelepidochrocitemiargyriteorpimentpyrolusite-pyrargyritepsilomelane

20berthieriteboulangeritecalcitechalcophanitegraphitemackinawitemarcasitemolybednitestibnitetenoritevalleriite