Lecture 14 Systematic Description of Minerals 1. Mineral Classifications

Principally by dominant anion or anionic group Secondarily by internal mineral structure

Native ElementNative ElementSulfides (S)Sulfides (S)Sulfosalts (SbSulfosalts (Sb22SS33))Oxides (O)Oxides (O)Hydroxides (OH)Hydroxides (OH)Halides (Cl, F, Br, I)Halides (Cl, F, Br, I)Carbonates (COCarbonates (CO33))Sulfates (SOSulfates (SO44))Phosphates (POPhosphates (PO44))Nitrates, Borates, Tungstates, Molybdates, Arsenates, Vanadates...Nitrates, Borates, Tungstates, Molybdates, Arsenates, Vanadates...

SilicatesSilicates NesosilicatesNesosilicates SorosilicatesSorosilicates CyclosilicatesCyclosilicates InosilicatesInosilicates PhyllosilicatesPhyllosilicates TectosilicatesTectosilicates

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

AuAu AgAg CuCu PtPt

Native Non-metalsSulfurSulfur DiamondDiamond GraphiteGraphite

SS88 ring molecules ring molecules bonded by weakbonded by weakvan der Waals van der Waals forcesforces

CC66 ring molecules ring molecules bonded by weakbonded by weakvan der Waals van der Waals forces; good forces; good electrical electrical conductivityconductivity

StrongStrongCovalentCovalentBondsBonds

Synthetic (industrial) DiamondsSynthetic (industrial) Diamonds

Native Element Occurrences

GoldGold – Hydrothermal fluids related to magmatism, especially late – Hydrothermal fluids related to magmatism, especially late fractionation; commonly occurs in veins of quartz and pyrite; may form fractionation; commonly occurs in veins of quartz and pyrite; may form detrital grains to produce placer deposits; Rarely occurs alloyed with detrital grains to produce placer deposits; Rarely occurs alloyed with other elements.other elements.

SilverSilver – Hydrothermal ore deposits rich in sulfides, arsenides, and – Hydrothermal ore deposits rich in sulfides, arsenides, and bismuthides; also commonly associated native copper.bismuthides; also commonly associated native copper.

Copper – Sulfide-poor hydrothermal ore deposits or secondary Copper – Sulfide-poor hydrothermal ore deposits or secondary oxidation of Cu-sulfide minerals; most abundant occurrence is the oxidation of Cu-sulfide minerals; most abundant occurrence is the native copper deposits of the Keweenawan Peninsula of Upper native copper deposits of the Keweenawan Peninsula of Upper Michigan where it occurs in lava flows and interflow conglomerates. Michigan where it occurs in lava flows and interflow conglomerates.

Native Element Occurrences

Platinum – Occurs as primary deposits in mafic intrusions and as Platinum – Occurs as primary deposits in mafic intrusions and as secondary placer deposits.secondary placer deposits.

Diamond – Occurs in mantle-derived Kimberlite pipes with other high Diamond – Occurs in mantle-derived Kimberlite pipes with other high temperature/high pressure minerals. Needs a subduction zone to temperature/high pressure minerals. Needs a subduction zone to pressurize ocean floor carbon, the a rising plume to hit the right depth pressurize ocean floor carbon, the a rising plume to hit the right depth in the subduction zone. That’s why they are rare.in the subduction zone. That’s why they are rare.

Sulfur – Precipitates near volcanic vents from volcanic gasses and Sulfur – Precipitates near volcanic vents from volcanic gasses and secondarily by oxidation of sulfide minerals. secondarily by oxidation of sulfide minerals.

Sulfides and Sulfosalts Most common ore source of metals XmSn

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 StabilityReducing to Oxidizing, Acidic to Basic Environments

Cu-HCu-H22O-OO-O22-S-CO-S-CO22 phase diagram phase diagramat 25°C and 1 atm pressureat 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 Minerals

PyPy

PoPo

CpCp

BnBn

CcCc

DgDg

CvCv

Other Common Sulfide Minerals

Galena PbS - dense, cubic cleavage

may contain substantial silver

Sphalerite (Zn,Fe)S – submetallic black to resinous yellow, brown lusterYellow streak

Pentlandite (Fe,Ni)9S8 – yellow-bronze; in magmatic ores

Cinnabar HgS – vermilion-red color, dense

Molybdenite MoS2 – silver metallic sheets

PtPt

GalenaGalena

Zn>>FeZn>>Fe

Zn>FeZn>Fe

ZnZn

Arsenosulfides, Arsenides and Sulfosalts

Cobaltite (Co,Fe)AsSCobaltite (Co,Fe)AsS – silver white metallic – silver white metallic

Arsenopyrite FeAsSArsenopyrite FeAsS – silver white metallic – silver white metallic

Realgar AsS Realgar AsS (red)(red) - Orpiment As - Orpiment As22SS33 (yellow)(yellow)

Stibnite SbStibnite Sb22SS33 silver-gray prisms silver-gray prisms

Enargite CuEnargite Cu33AsSAsS44 – striated metallic columns – striated metallic columns and blades – a sulfosaltand blades – a sulfosalt

Skutterudite (Co,Ni)AsSkutterudite (Co,Ni)As33 silver-gray cubes silver-gray cubes

(Antimony sulfide)