GY 302: Crystallography & MineralogyGY 302: Crystallography & MineralogyUNIVERSITY OF SOUTH ALABAMALecture 8: Native ElementsLecture 8: Native ElementsLast 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). PPLPPLXNXNOptical PropertiesB: 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–neor ne-no. For biaxial crystals; na–ncor nc-na.As far as you are concerned, you see pretty colours under XNOptical PropertiesOptical PropertiesB: 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 PropertiesPPL XNB: 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. PPLPPLXNXNOptical PropertiesToday’s AgendaNative elements1. Chemistry and Crystallography (properties)2. Occurrences and Associations 3. Economics (resources, reserves, extraction)Featured Minerals: Gold and DiamondsToday’s AgendaNative elements1. Mineral Classes/Properties2. Chemistry and Crystallography (properties)3. Occurrences and Associations 4. Economics (resources, reserves, extraction)Featured minerals: Gold, DiamondsNative ElementsCopper Cu IsometricGold Au* IsometricSilver Ag* IsometricPlatinum Pt* IsometricArsenic As HexagonalAntimony Sb HexagonalBismuth Bi HexagonalTellurium Te TrigonalSulfur S OrthorhombicGraphite C* HexagonalDiamond C* IsometricMetalsSemi-metalsNon-metals* primary production from native elementsMetallic Native ElementsGold (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.infoMetallic Native ElementsGold (Au)Occurrence: quartz veins (igneous rocks, hydrothermal), placer depositsAssociated Mins: quartz, pyrite, chalcopyrite, galena, stibnite, sphalerite, arsenopyrite, tourmaline, molybdeniteRelated Mins:Calaverite [AuTe2], sylvanite[(Au,Ag)Te2], maldonite[Au2Bi], electrum [Au-Ag solid solution]http://www.usagold.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 ounceshttp://minerals.usgs.gov/minerals/pubs/mcs/2011/mcs2011.pdfMetallic 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 todayProduction: refined metal produced per year (metric tons)(see lecture suppliments for additional resources jargon)Metallic Native ElementsGold (US data)2011 Mineral Commodity Summaries. USGSMetallic Native ElementsSilver (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=1060Metallic Native ElementsSilver (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 GroupOccurrence: ultramafic rocks and in placer deposits.Associated Mins: chromite, spineland olivineRelated Mins:noneMetallic Native ElementsPlatinum Group (US data)2011 Mineral Commodity Summaries. USGSNon-metallic Native ElementsGraphite (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: opaqueName derivation: From the Greek, graphein, "to writeNon-metallic Native ElementsGraphite (C)Occurrence: metamorphic rocks (esp. schists, marbles and gneisses). Rare in igneous rocks. Associated Mins: none to speak ofRelated Mins:noneNon-metallic Native ElementsDiamond (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 ElementsDiamond (C)Occurrence: altered ultramafic rocks and carbonated igneous rocks (Kimberlites)Associated Mins: olivine, pyrope, zircon, kyaniteRelated Mins:noneMetallic Native ElementsDiamond (production, reserves in 1000s of karats of gem quality stone)2011 Mineral Commodity Summaries. USGSNon-metallic Native ElementsGemstones (US data)2008 Mineral Commodity Summaries. USGSEmplacement and ExtractionGoldGold is largely produced through hydrothermal precipitationGoldGold is largely produced through hydrothermal precipitationhttp://www.chesapeakegold.com/images/maps/hydrothermal-2-full.gifGoldGold is largely produced through hydrothermal precipitationhttp://gsc.nrcan.gc.ca/mindep/synth_dep/gold/vms/pdf/deposit_synthesis.gold_vms.dube.pdfGoldAustralian Gold DepositsGoldHemlo Gold