Minerals Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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There are several thousand minerals in the world, but only about 100 are common. Minerals are inorganic, homogeneous, crystalline solids withdefinite physical properties and chemical composition. They are commonly defined by their chemical composition. Elements are minerals such as gold or copper that are composed of a single kind of atom. All other minerals are compounds of two or more elements. Minerals are chemically bonded in their atomic structure by the sharing of electrons. They are commonly classified by the negative part of their chemical bond (negative ion) into groups such as: sulfides, halides, oxides, borates, silicates, carbonates, sulfates, phosphates, and chromates.

Minerals are crystalline and can be classified by their crystallographic characteristics. The atoms in minerals have properties that organize them into geometrical forms (crystals) such as cubes like halide (common table salt) or sheets (mica). Mineral crystals are classified into seven systems: isometric, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, and triclinic.

The physical characteristics of minerals used to identify a specimen include luster, cleavage, hardness, and color. The luster of a mineral is the manner in which its surface reflects light. The luster may be either metallic or nonmetallic. Minerals like gold nuggets or lumps of “fool’s gold” (iron sulfides or pyrites) have a shiny metallic luster. Minerals have a nonmetallic luster if the surface looks vitreous (glassy like quartz), pearly (talc), resinous, silky, or is dull and clay-like. The Mohs hardness scale classifies minerals by their hardness on a scale from 1 to 10. The color of minerals depends on their chemical composition. Mineral colors range from white to black with the colors of the rainbow in between. However, the color of a mineral may have been affected by chemical impurities in the formation process.

Some minerals may be recognized by their habit (general appearance). Streak tests are used to identify minerals. After a mineral is rubbed across a rough porcelain plate, the streak it produced is examined for its color. Flame tests to identify minerals use a bit of the mineral specimen ground into a powder. When the mineral powder is burned the color will aid in identification. Chemical tests are used to identify minerals, even in the field.

Minerals are usually formed in various kinds of solutions. The core of the earth is molten magma. As magma wells up from the center of the earth it fractures the crust, melts the rock in its vicinity, and superheats water. As the liquid rock solutions cool, crystals form. Crystals also form when they precipitate out of solutions of hot gases or hot water in fracture veins. Crystals also form from sublimation in cooling volcanic vapors, by chemical reactions to air, water, or other minerals, and by the evaporation of salt lakes or seas.

Mineral deposits are classified by their manner of formation. Igneous actions produce magmatic and pegmatic minerals such as diamonds or corundum. Mineral deposits can form by metamorphic contact (metasomatism), or from magmatic gases (pneumatolysis). Sedimentary action can produce iron ores. Evaporites, such as gypsum, salt, and potash, are solid remains from evaporation. Some deposits are the residue of erosion or other forces. Miners and others seek mineral deposits to work for commercial gain; for them, these include some substances such as granite, oil, gas, opal, and amber that are not true minerals.

Bibliography:

C. Bishop et al., Cambridge Guide to Minerals, Rocks and Fossils (Cambridge University Press, 2001);
Walter Borchardt-Ott, Crystallography (Springer-Verlag, 1995);
Ole Johnsen, Photographic Guide to Minerals of the World (Oxford University Press, 2002);
Kennie Lyman, , Simon & Schuster’s Guide to Gems and Precious Stones (Simon & Schuster, 1986);
Frederick Pough, A Field Guide to Rocks and Minerals (Houghton Mifflin, 1997);
Putnis, Introduction to Mineral Sciences (Cambridge University Press, 1992);
Donald E. Sands, Introduction to Crystallography (Dover Publications, 1975);
Walter Schumann, Minerals of the World (Sterling Publishing , 1992).