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Minerals and Rocks Rocks • Aggregates (mixture—can be separated) of minerals. Minerals • Four Characteristics: – Naturally occurring – Inorganic (was never alive) – Solid – Possesses a definite chemical structure Properties of Minerals • Crystal form— external expression of internal structure Properties of Minerals • Color—unreliable in identifying minerals Properties of Minerals • Streak—the color of a mineral in its powder form—obtained by rubbing the mineral across a hard, unglazed porcelain Properties of Minerals • Hardness—resistance of a mineral to abrasion or scratching – Mohs scale—hardness scale ranging from 10 (hardest) to 1 (softest) – Diamond is 10, talc is 1 Properties of Minerals • Cleavage—tendency of a mineral to break along planes of weak bonding Properties of Minerals • Fracture—do not exhibit cleavage when broken • Specific gravity—the weight of a mineral compared to the same volume of water Mineral Groups • Silicates – Silicon and oxygen are the two most abundant elements in the Earth’s crust; they form silicates – All have the same basic structure—the silicon-oxygen tetrahedron—four oxygen atoms surrounding a silicon atom – Other elements join the tetrahedrons together in chains, sheets, or threedimensional networks. – Feldspars are most abundant, with quartz second Mineral Groups • Carbonates – Calcite • Limestone—used in building and paving • Marble—used decoratively • Halite (salt) and Gypsum also found in sedimentary rock Mineral Resources • Reserves—already identified deposits from which minerals can be extracted profitably • Ores—useful metallic minerals that can be mined at a profit • Changing economic factors determine whether a deposit is profitable to extract