Lecture 14 Systematic Description of Minerals 1. Mineral Classifications  Principally by dominant anion or anionic group  Secondarily by internal mineral structure Native Element Sulfides (S) Sulfosalts (Sb 2 S 3 ) Oxides (O) Hydroxides (OH) Halides (Cl, F, Br, I) Carbonates (CO 3 ) Sulfates (SO 4 ) Phosphates (PO 4 ) Nitrates, Borates, Tungstates, Molybdates, Arsenates, Vanadates... Silicates Nesosilicates Nesosilicates Sorosilicates Sorosilicates Cyclosilicates Cyclosilicates Inosilicates Inosilicates Phyllosilicates Phyllosilicates Tectosilicates Tectosilicates

Minerals for term paper electronics

Native Elements and Sulfides are frequently the targets of mining companies

Native Elements  Metals – Gold, Silver, Copper, Platinum, Palladium, Osmium, Iridium, Iron, Fe-nickel  Semi-metals – Arsenic, Bismuth, Antimony  Non-metals – Sulfur, Diamond, Graphite

Native Metals  metallic bonding  dense, cubic close packing (“CCP”)  properties: soft, malleable, ductile, sectile, good heat and electrical conductors  Melting points: low-Au, Ag, Cu Au AgCuPt

Native Non-metals SulfurDiamondGraphite S 8 ring molecules bonded by weak van der Waals forces C 6 ring molecules bonded by weak van der Waals forces; good electrical conductivity StrongCovalentBonds Synthetic (industrial) Diamonds

Native Element Occurrences Gold – Hydrothermal fluids related to magmatism, especially late fractionation; commonly occurs in veins of quartz and pyrite; may form detrital grains to produce placer deposits; Rarely occurs alloyed with other elements. Silver – Hydrothermal ore deposits rich in sulfides, arsenides, and bismuthides; also commonly associated native copper. Copper – Sulfide-poor hydrothermal ore deposits or secondary oxidation of Cu-sulfide minerals; most abundant occurrence is the native copper deposits of the Keweenawan Peninsula of Upper Michigan where it occurs in lava flows and interflow conglomerates.

Native Element Occurrences Platinum – Occurs as primary deposits in mafic intrusions and as secondary placer deposits. Diamond – Occurs in mantle-derived Kimberlite pipes with other high temperature/high pressure minerals. Needs a subduction zone to pressurize ocean floor carbon, the a rising plume to hit the right depth in the subduction zone. That’s why they are rare. Sulfur – Precipitates near volcanic vents from volcanic gasses and secondarily by oxidation of sulfide minerals.

Sulfides and Sulfosalts  Most common ore source of metals  X m S n  As (arsenic) may substitute for S giving rise to sulfarsenides, and arsenides  X= Fe, Cu, Zn, Pb, Ni, Co, Hg, Mo  Magmatic and hydrothermal origin  Sulfosalts, As, Sb, and Bi take the place of metals (X)

Sulfide Stability Reducing to Oxidizing, Acidic to Basic Environments Cu-H 2 O-O 2 -S-CO 2 phase diagram at 25°C and 1 atm pressure Eh-pH diagrams are used for reactions that occur from aqueous solutions at low pressures. The voltage across a galvanic cell and the pH determine which mineral precipitates in a laboratory vessel containing all needed elements. These atmospheric pressure conditions model the formation of many major ores

High Temperature Low Pressure Sulfide formation at MORs

Cu-Fe Sulfide MineralsPy Po Cp Bn Cc Dg Cv

Other Common Sulfide Minerals  Galena PbS - dense, cubic cleavage may contain substantial silver  Sphalerite (Zn,Fe)S – submetallic black to resinous yellow, brown luster Yellow streak  Pentlandite (Fe,Ni) 9 S 8 – yellow- bronze; in magmatic ores  Cinnabar HgS – vermilion-red color, dense  Molybdenite MoS 2 – silver metallic sheets Pt Galena Zn>>Fe Zn>Fe Zn

Arsenosulfides, Arsenides and Sulfosalts Cobaltite (Co,Fe)AsS – silver white metallic Arsenopyrite FeAsS – silver white metallic Realgar AsS (red) - Orpiment As 2 S 3 (yellow) Stibnite Sb 2 S 3 silver-gray prisms Enargite Cu 3 AsS 4 – striated metallic columns and blades – a sulfosalt Skutterudite (Co,Ni)As 3 silver-gray cubes (Antimony sulfide)