mica (redirected from micaceous)

mica (mī`kə), general term for a large group of minerals, hydrous silicates of aluminum and potassium, often containing magnesium, ferrous iron, ferric iron, sodium, and lithium and more rarely containing barium, chromium, and fluorine. All crystallize in the monoclinic system, but mica is most commonly found in the form of scales and sheets. All the micas have an excellent basal cleavage, splitting into very thin, elastic laminae. Some varieties are transparent; resistance to heat is high. Commercially, the most important micas are muscovite (potassium mica) and phlogopite (magnesium mica). Muscovite, the commoner variety, is usually colorless, but it may be red, yellow, green, brown, or gray, with a vitreous to pearly luster. It occurs in granites, syenites, mica schists, and gneisses, but is most common in pegmatite dikes. It is widely distributed. Phlogopite varies in color from yellow to brown, some specimens having a coppery tint and others being greenish. It occurs in crystalline limestones, dolomites, and serpentines in Canada, New York, New Jersey, and Finland. Mica mining, because of the necessity of keeping the crystals intact, is a delicate operation; drills and blasting powder must be used carefully, if at all. The mined crystals are first "cobbed," i.e., roughly trimmed of rock and cut, then split with a hammer into plates, and further split into sheets with a knife. Sheet mica is used as an insulating material and as a resonant diaphragm in certain acoustical devices. Scrap and ground mica is used in wallpaper, fancy paint, ornamental tile, roofing, lubricating oil, and Christmas-tree snow. Ground mica is sometimes pressed into sheets (micanite) that can be used as sheet mica. Most of the sheet mica used in the United States is imported, chiefly from India and also from Brazil. Synthetic mica was produced in the United States after intensive government-sponsored research began in 1946.

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mica

Any of a group of hydrous potassium, aluminum silicate minerals that exhibit a two-dimensional sheet, or layer, structure. A very abundant variety of mica is muscovite; two other common varieties are biotite and phlogopite. Micas have various industrial uses. The varieties that contain little iron are used as thermal or electrical insulators in appliances and in such electrical devices as capacitors. In ground form, micas are used in the manufacture of wallpaper, roofing paper, and paint. Ground micas also serve as lubricants, absorbents, and packing material.

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mica

any of a group of lustrous rock-forming minerals consisting of hydrous silicates of aluminium, potassium, etc., in monoclinic crystalline form, occurring in igneous and metamorphic rock. Because of their resistance to electricity and heat they are used as dielectrics, in heating elements, etc.