Post on 29-Dec-2015
description
transcript
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
B: Crossed Nichols (XN)
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
B: Crossed Nichols (XN)
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
B: Crossed Nichols (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
Metallic Native Elements
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
ww
.usa
gold
.com
/
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 Elements
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
Metallic Native Elements
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
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
Non-metallic Native Elements
Graphite (C)Occurrence: metamorphic rocks (esp. schists, marbles and gneisses). Rare in igneous rocks.
Associated Mins: none to speak of
Related Mins: none
Non-metallic Native Elements
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}
─
Non-metallic Native Elements
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)
2011 Mineral Commodity Summaries. USGS
GoldGold is largely produced through hydrothermal precipitation
http://www.chesapeakegold.com/images/maps/hydrothermal-2-full.gif
GoldGold is largely produced through hydrothermal precipitation
http://gsc.nrcan.gc.ca/mindep/synth_dep/gold/vms/pdf/deposit_synthesis.gold_vms.dube.pdf
Gold ExtractionCyanide Leeching Method
4Au + 8CN- + O2 + 2H2O = 4Au(CN)2- + 4OH-
http://www.daa.com.au/uploads/RTEmagicC_mm_leachfeed.jpg.jpg
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