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MINERALOGY Some Common Minerals Illustrated by Charina Cameron Mineral Groups • • • • • Nearly 4000 minerals Only a few dozen are abundant in Earth’s crust These are the rock-forming minerals 8 elements comprise the bulk of these minerals They also represent 98% of the continental crust: – – – – – – – – O Si Al Fe Ca Na K Mg 47% 28% 8% 5% 4% 3% 3% 2% Silicate minerals Major Properties of Minerals • • • • • • Crystal form Luster (metallic, non-metallic, etc.) Colour (often due to impurities) Streak (colour of powder) Hardness (Moh’s scale: 1 to 10) Cleavage – none or up to 6 surfaces – planes of weakness in crystal structure • Fracture (conchoidal, etc.) • Specific gravity – density compared to water – galena is much greater than quartz (2.65) Special Mineral Properties • • • • • • Magnetic Elastic malleable taste smell feel – Soapy – Greasy • Double refraction • Reaction to HCl Moh’s HARDNESS SCALE 1 7 4 Quartz Fluorite Talc 8 Topaz 2 5 Gypsum 9 Apatite 6 3 Corundum 10 Orthoclase Calcite Diamond Common Mineral Groups • • • • • • • • Sulfides Oxides Carbonates Sulphates Phosphates Halides Native elements Silicates S2O2(CO3)2(SO4)2(PO4)3F,Cl, etc. Au, Cu, C, etc. (SiO4)4- SULFIDES • Pyrite • FeS2 • Sphalerite • (Zn,Fe)S Chalcopyrite (Cu,Fe)S2 Galena PbS OXIDES • Hematite – Fe2O3 • Corundum – Al2O3 Limonite Magnetite Fe2O3 nH2O Fe3O4 CARBONATES • Double refraction in Calcite CaCO3 • Dolomite crystals (Ca,Mg)CO3 • Siderite • FeCO3 CARBONATES • Calcite crystals from a vein in Wolfville Formation, showing 3 perfect cleavages not at right angles CARBONATES • Hexagonal Calcite crystals from Scots Bay Fm SULPHATES • Gypsum CaSO4nH2O • Anhydrite CaSO4 PHOSPHATES • Apatite Ca3(PO4)2 HALIDES • Fluorite CaF2 4 cleavages • Halite NaCl 3 cleavages at right angles NATIVE ELEMENTS • Sulphur S8 • Gold Au tiny nuggets panned at Ovens, Nova Scotia • Graphite C • Diamond C