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GY 302: Crystallography &

Mineralogy

GY 302: Crystallography &

Mineralogy

UNIVERSITY OF SOUTH ALABAMA

Lecture 8: Native ElementsLecture 8: Native Elements

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Last Time

1. Mineral properties under XN (crossed Nichols/polars)

2. Mineral Classes/Properties

3. Native Elements; Chemistry & Crystallography(properties)

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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

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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 orne - no.For biaxial crystals; n

a

nc

ornc

- na

.

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

Optical Properties

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Optical Properties

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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

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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

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Todays Agenda

Native elements1. Chemistry and Crystallography (properties)

2. Occurrences and Associations

3. Economics (resources, reserves, extraction)

Featured Minerals: Gold and Diamonds

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Todays Agenda

Native elements1. Mineral Classes/Properties

2. Chemistry and Crystallography (properties)

3. Occurrences and Associations

4. Economics (resources, reserves, extraction)

Featured minerals: Gold, Diamonds

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Native Elements

Copper Cu Isometric

Gold Au* Isometric

Silver Ag* Isometric

Platinum Pt* Isometric

Arsenic As HexagonalAntimony Sb Hexagonal

Bismuth Bi Hexagonal

Tellurium Te Trigonal

Sulfur S Orthorhombic

Graphite C* Hexagonal

Diamond C* Isometric

Metals

Semi-metals

Non-metals

* primary production from native elements

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Metallic Native Elements

Gold (Au)Crystal: IsometricPt. Group: 4/m32/m

Habit: octahedral, dendritic

SG: 15.6-19.3 (depending on Ag content)H: 2.5-3*

L: metallic

Col: gold-yellow

Str: gold-yellowClev: none

Optical: Opaque

Name Derivation: Anglo Saxon, of uncertain origin.

http://www.rocksandgems.info

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Gold (Au)Occurrence: quartz veins (igneousrocks, 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://www.usagold.com/

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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

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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)

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Gold (US data)

2011 Mineral Commodity Summaries. USGS

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Silver (Ag)Crystal: IsometricPt. Group: 4/m32/m

Habit: massive, acicular

SG: 10.1-10.5H: 2.5-3

L: metallic

Col: silver-white

Str: gold-yellowClev: none

Optical: Opaque

Name: Derivation: Anglo Saxon, of uncertain origin.

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

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Silver (Ag)Occurrence: hydrothermal depositsand 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]

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Platinum Group (Pt, Ir, Pa, Rh, Ru, Os,)

Crystal: IsometricPt. Group: 4/m32/m

Habit: massive, acicular

SG: 21.47H: 4-4.5

L: metallic

Col: gray-silver

Str: gray-silverClev: none

Optical: opaque

Name Derivation: Spanish, platina = "silver."

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Platinum GroupOccurrence: ultramafic rocks and in

placer deposits.

Associated Mins: chromite, spinel

and olivine

Related Mins: none

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Platinum Group (US data)


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Non-metallic Native Elements

Graphite (C)Crystal: HexagonalPt. Group: 6/m 2/m 2/m

Habit: platey, massive

SG: 2.1-2.2H: 1-2

L: submetallic

Col: lead-gray, black

Str: blackClev: perfect basal {001}

Optical: opaque

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

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

in igneous rocks.

Associated Mins: none to speak of

Related Mins: none

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Diamond (C)Crystal: IsometricPt. Group: 4/m32/m

Habit: octahedral, twinned

SG: 3.5H: 10

L: adamantine

Col: colorless, rare blue, red,

yellowStr: n/a

Optical: isotropic, n=2.419

Clev: perfect {111}

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Diamond (C)Occurrence: altered ultramafic rocksand carbonated igneous rocks

(Kimberlites)

Associated Mins: olivine, pyrope,zircon, kyanite

Related Mins: none

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Diamond (production, reserves in 1000s of karats of gem quality stone)


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Gemstones (US data)


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Emplacement and Extraction

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GoldGold is largely produced through hydrothermal precipitation

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

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

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GoldAustralian Gold Deposits

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Gold

Hemlo Gold

play

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Gold

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Gold

Golden Giant Mine (Newmont)

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Gold

Golden Giant Mine

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Gold

Golden Giant Mine

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Gold Extraction

Golden Giant Mine

A typical

underground mine

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Gold Extraction

Waihi open pit gold mine (Newmont),

New Zealand

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Gold Extraction

Summitville (Co) Gold Mine

An atypical open

pit mine

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Gold Extraction

Cyanide Leeching Method

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

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

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Gold ExtractionHeap Cyanide

LeechingMethod

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Diamonds

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Diamonds

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

Diamond

Phase diagram

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Diamond

Kimberlite Pipes

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

http://www.earth.ox.ac.uk/~oesis/field/medium/kimberlite.jpg

Diamonds

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Diamond

Kimberlite Pipes

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

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

Diamonds

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Diamonds

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Diamonds

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Diamonds

Etaki Mine

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Diamonds

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

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Diamonds

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

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Todays Homework

1.1. Finish Lab Assignment 5 (Optical mineralogy)Finish Lab Assignment 5 (Optical mineralogy)

Next Lecture1. The Sulfides part 1

Documents

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