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Earth Materials Unit 2 Chapters 3-5 in text Minerals I. Composition of minerals a. Most rocks have a number of different minerals in them. b.The element oxygen is the most common element found in the earth’s crust. c. Silicon is usually found bonded with oxygen in most minerals. d.The most common class of minerals contains the silicates, the basis of which is the silicon-oxygen tetrahedra. II. Rock-forming minerals a. Oxides contain elements, often metals, and oxygen b.Sulfides are usually metals and sulfur c. Calcium Carbonates include calcite d.Ferrous minerals contain iron (Fe) III. New York State Minerals a. garnet-used as abrasives, found in metamorphic rock in Adirondacks b.gypsum, a sulfur-bearing rock, found where ancient seas dried up in central/western NY c. Halite and other salts, from deposits left by evaporating seas d.Wollastonite, an evaporite. IV. The 5 properties of all minerals 1.They are all solid 2.All minerals have a basic crystal structure: orderly internal pattern of units 3.All minerals have a definite chemical composition, which means that their elements are always in the same ratio 4.They are inorganic (do not come from living things or the remains of living things). 5.They are naturally occurring, not anthropogenic V. Mineral Identification 1.Luster- the manner in which the mineral _shines in reflected light Metallic luster; if polished, it would look like silver, gold or black metal. Opaque, heavy and dark. Non-metallic luster; anything that does not look like a metal. Ex. Pearly, earthy, dull, glassy 2.Specific gravity- compares the density of the mineral to the density of water.\ 3.Hardness- a measure of the minerals resistance to being scratched. Moh’s scale of hardness compares minerals to each other. (talc is 1, _diamond_ is 10). 4. Cleavage vs. fracture: description of the mineral’s tendency to break along definite angles and planes. Very hard to use without being able to repeatedly break samples. cleavage describes clean, patterned breaks, while fracture indicates a lack of pattern to the break. 5.Streak- the color of the powdered form of a mineral, obtained from dragging it along an unglazed porcelain plate 6.Color- color is not always helpful, because one mineral may have trace amounts of metal and other impurities that will change the color. 7.Other specific tests/indicators such as: a. sulfur smells b.calcite (CaCO3) fizzes even in weak acids c. magnetite is magnetic d.iron rusts e. halite tastes salty f. flame tests can accurately identify minerals and elements