Chapter 2 - Minerals.docx

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Earth Sciences
Earth Sciences 1022A/B
Stephen R Hicock

Minerals 9/13/2012 9:16:00 AM Mineralogy  study of minerals Rock - any solid mass of mineral that occurs naturally as part of our planet - most are aggregate of various minerals Definition of Minerals Minerals Variation of Minerals  solid chemical compound that is found in nature  chemical compounds that combine to form rocks  every mineral is a molecule  hardness, cleavage varies depending on element composition  4000 minerals, 20 common  some have same chemical composition but different physical characteristics  polymorphs eg. Graphite and Diamonds Criteria 1. occur naturally 2. solid at surface temp and pressure 3. posses orderly internal structure, atoms arranged in pattern 4. definite chemical composition 5. usually inorganic Cleavage Cleavage  how minerals break along the weakest plains Crystal Habit (shape) • external expression of a mineral Lustre • quality of light reflected from the surface Streak • colour of mineral in powdered form Hardness ** • mineral’s resistance to abrasion, measured on Mohs scale Fracture • minerals that have similar strength in all directions and lack ability to cleavage can fracture in distinctive manner. Eg. conchoidal fracture (curved like glass) Specific Gravity • number representing ratio of weight of mineral to weight of an equal Double refraction - when placed over letter, reflects twice Common Minerals Common Minerals Silicates Most abundant mineral  most abundant;  made of the silicon-oxygen tetrahedron Silicon-oxygen (silica, (Si4 ) ) bonded to various metallic tetrahedron. cations tetra = 4, hedron = pyramid Common Silicate Minerals Ferromagnesian Ferromagnesian (dark) silicates: kinds. contain Fe and Mg cations Olivine olivine - single silica tetrahedral bonded to Fe+2, Mg +2 ions - grass-green in colour - found deep in crust Pyroxene pyroxene
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