Mineralogy & Crystallography

GY 302: Crystallography & Mineralogy

GY 302: Crystallography & Mineralogy

UNIVERSITY OF SOUTH ALABAMA

Lecture 8: Native ElementsLecture 8: Native Elements

Last Time1. Mineral properties under XN (crossed Nichols/polars)

2. Mineral Classes/Properties3. Native Elements; Chemistry & Crystallography

(properties)

B: Crossed Nichols (XN)

6) Extinction: occurs when the indicatrix aligns up with the polars and the entire crystal goes black (extinct).

PPLPPL XNXN

Optical Properties


7) Birefringence. This is the most important property of minerals under crossed polars. It is defined as the difference between the index of refraction of the minimum and maximum refractive indices of a mineral.

For uniaxial minerals; no – ne or ne - no. For biaxial crystals; na – nc or nc - na.

As far as you are concerned, you see pretty colours under XN

Optical Properties

Optical Properties


8) Optical Twinning. Same thing as physical twins whereby two or more crystals of a single mineral grow together in a mathematically predicable pattern (involves twin planes, twin axes etc).

Optical Properties

PPL XN


9) Zonation. Some minerals change their composition has they grow, particularly those that that form continuous series through solid solution during igneous processes (e.g., olivine, plagioclase). This can result in optical zonation.

PPLPPL XNXN

Optical Properties

Today’s Agenda

Native elements1. Chemistry and Crystallography (properties)2. Occurrences and Associations 3. Economics (resources, reserves, extraction)

Featured Minerals: Gold and Diamonds

Today’s Agenda

Native elements1. Mineral Classes/Properties2. Chemistry and Crystallography (properties)3. Occurrences and Associations 4. Economics (resources, reserves, extraction)

Featured minerals: Gold, Diamonds

Native Elements

Copper Cu IsometricGold Au* IsometricSilver Ag* IsometricPlatinum Pt* IsometricArsenic As HexagonalAntimony Sb HexagonalBismuth Bi HexagonalTellurium Te TrigonalSulfur S OrthorhombicGraphite C* HexagonalDiamond C* Isometric

Metals

Semi-metals

Non-metals

* primary production from native elements

Metallic Native Elements

Gold (Au)Crystal: IsometricPt. Group: 4/m32/mHabit: octahedral, dendriticSG: 15.6-19.3 (depending on Ag content)

H: 2.5-3* L: metallicCol: gold-yellowStr: gold-yellowClev: noneOptical: Opaque

─

Name Derivation: Anglo Saxon, of uncertain origin.

http://www.rocksandgems.info


Gold (Au)Occurrence: quartz veins (igneous rocks, hydrothermal), placer deposits

Associated Mins: quartz, pyrite, chalcopyrite, galena, stibnite, sphalerite, arsenopyrite, tourmaline, molybdenite

Related Mins: Calaverite [AuTe2], sylvanite [(Au,Ag)Te2], maldonite[Au2Bi], electrum [Au-Ag solid solution]

http

://w

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gold

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Metallic Native ElementsGold (production, reserves in tonnes*)

Production: refined metal produced per year (metric tons)*1 metric ton (tonne) = 1000 kg = 32,150.7 troy ounces

http://minerals.usgs.gov/minerals/pubs/mcs/2011/mcs2011.pdf

Metallic Native ElementsResources: a concentration of a material useful to humanity (water, food, minerals)

Geological Resources: all materials (mineral and energy) including those only surmised to exist, that have present or anticipated future value and which can be extracted from the Earth via economically feasible methods ($$$) (i.e., gold, diamonds, coal, oil, natural gas, water)

Reserve Base: The in-place demonstrated (measured+indicated) amount of a resource that can be extracted via current mining and production techniques (currently economical + marginal +/- subeconomical) . Equivalent to the old “geological reserve” definition.

Reserve (current): That part of the reserve base that could be economically extracted today

Production: refined metal produced per year (metric tons)

(see lecture suppliments for additional resources jargon)

Metallic Native ElementsGold (US data)

2011 Mineral Commodity Summaries. USGS


Silver (Ag)Crystal: IsometricPt. Group: 4/m32/mHabit: massive, acicularSG: 10.1-10.5H: 2.5-3 L: metallicCol: silver-whiteStr: gold-yellowClev: noneOptical: Opaque

─

Name: Derivation: Anglo Saxon, of uncertain origin.

http://webmineral.com/specimens/picshow.php?id=1060


Silver (Ag)Occurrence: hydrothermal deposits and in oxidized zones of ore deposits.

Associated Mins: arsenopyrite, Ni and As ores.

Related Mins: dyscrasite [Ag3Sb], argentite [Ag2S], proustite[Ag3AsS3], pyrargyrite [Ag3SbS3], amalgram [Hg-Ag solid solution]; electrum [Au-Ag solid solution]

Metallic Native ElementsPlatinum Group (Pt, Ir, Pa, Rh, Ru, Os,)

Crystal: IsometricPt. Group: 4/m32/mHabit: massive, acicularSG: 21.47H: 4-4.5 L: metallicCol: gray-silverStr: gray-silverClev: noneOptical: opaque

─

Name Derivation: Spanish, platina = "silver."

Metallic Native ElementsPlatinum Group

Occurrence: ultramafic rocks and in placer deposits.

Associated Mins: chromite, spineland olivine

Related Mins: none

Metallic Native ElementsPlatinum Group (US data)


Non-metallic Native Elements

Graphite (C)Crystal: HexagonalPt. Group: 6/m 2/m 2/mHabit: platey, massiveSG: 2.1-2.2H: 1-2 L: submetallicCol: lead-gray, blackStr: blackClev: perfect basal {001}Optical: opaque

Name derivation: From the Greek, graphein, "to write


Graphite (C)Occurrence: metamorphic rocks (esp. schists, marbles and gneisses). Rare in igneous rocks.

Associated Mins: none to speak of

Related Mins: none


Diamond (C)Crystal: IsometricPt. Group: 4/m32/mHabit: octahedral, twinnedSG: 3.5H: 10 L: adamantineCol: colorless, rare blue, red,

yellowStr: n/aOptical: isotropic, n=2.419Clev: perfect {111}

─


Diamond (C)Occurrence: altered ultramafic rocks and carbonated igneous rocks (Kimberlites)

Associated Mins: olivine, pyrope, zircon, kyanite

Related Mins: none

Metallic Native ElementsDiamond (production, reserves in 1000s of karats of gem quality stone)


Non-metallic Native ElementsGemstones (US data)


Emplacement and Extraction

GoldGold is largely produced through hydrothermal precipitation


http://www.chesapeakegold.com/images/maps/hydrothermal-2-full.gif


http://gsc.nrcan.gc.ca/mindep/synth_dep/gold/vms/pdf/deposit_synthesis.gold_vms.dube.pdf

GoldAustralian Gold Deposits

GoldHemlo Gold

play

Gold

GoldGolden Giant Mine (Newmont)

GoldGolden Giant Mine

GoldGolden Giant Mine

Gold ExtractionGolden Giant Mine

A typical underground mine

Gold ExtractionWaihi open pit gold mine (Newmont),

New Zealand

Gold ExtractionSummitville (Co) Gold Mine

An atypical open pit mine

Gold ExtractionCyanide Leeching Method

4Au + 8CN- + O2 + 2H2O = 4Au(CN)2- + 4OH-

http://www.daa.com.au/uploads/RTEmagicC_mm_leachfeed.jpg.jpg

Gold ExtractionHeap Cyanide

Leeching Method

Diamonds

Diamonds

http://members.tm.net/lapointe/Carbon_Phase_Diagram.gif

Diamond Phase diagram

Diamond Kimberlite Pipes

http://www.kimcordiamonds.com/formation.phphttp://www.earth.ox.ac.uk/~oesis/field/medium/kimberlite.jpg

Diamonds

Diamond Kimberlite Pipes

http://www.kimcordiamonds.com/formation.php

http://gsc.nrcan.gc.ca/diamonds/kirkland/images/c14_3.jpg

Diamonds

Diamonds

Diamonds

Diamonds

Etaki Mine

Diamonds

http://gsc.nrcan.gc.ca/mindep/synth_prov/slave/pdf/regional_synthesis.slave.bleeker.pdf

Diamonds

http://gsc.nrcan.gc.ca/mindep/synth_prov/slave/pdf/regional_synthesis.slave.bleeker.pdf

Today’s Homework1.1. Finish Lab Assignment 5 (Optical mineralogy)Finish Lab Assignment 5 (Optical mineralogy)

Next Lecture1. The Sulfides part 1

Mineralogy & Crystallography

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