Earth Sciences 1022A/B Lecture Notes - Lecture 2: Drywall, Plagioclase, Biotite
11 Apr 2016
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Document Summary
Minerals are solid chemical compounds that combine to form rocks: they are found in nature and vary in atomic bonding, molecular structure, and element composition, all of which determine their chemical, physical properties and permit their identification. An infinite number of chemical combinations are possible and almost 4000 natural minerals are known; however, only about 20 minerals dominate the earth"s crust. Natural solid compounds found commonly in earth"s crust. Most abundant; made of the silicon-oxygen tetrahedron (silica, (sio4)-4) bonded to various metallic cations. Ferromagnesian (dark) silicates: contain fe+2 and mg+2 cations. Olivine (grass green colour) - covalently-bonded silica tetrahedra surrounded by. Fe, mg cations; fe, mg substitute for each other to form a group of minerals. Pyroxene - single chains of tetrahedra ionically bonded to metallic cations, nearly right angle cleavage; Amphibole - double chains of tetrahedra ionically bonded to metallic cations, 120 cleavage; Biotite (black mica) tetrahedral sheets ionically sandwich k+, perfect platy cleavage; sheets with perfect (basal) cleavage.
