mica

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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 Group of common rock-forming minerals characterized by a platy or flaky appearance. All contain aluminium, potassium and water; other metals, such as iron and magnesium, may be present. Micas have perfect basal cleavage. Common micas are muscovite and the biotite group. Muscovite is commonly found in coarse-grained acidic rocks, schists and gneisses, and in sedimentary rocks. The biotite micas are found in a wide range of igneous and metamorphic rocks, but more rarely in sedimentary rocks.

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mi·ca / ˈmīkə/ • n. a shiny silicate mineral with a layered structure, found as minute scales in granite and other rocks, or as crystals. It is used as a thermal or electrical insulator. DERIVATIVES: mi·ca·ceous / mīˈkāshəs/ adj.

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MICA

MICA (Heb. מִיכָא; "who is like [El]"), son of *Mephi-Bosheth, son of Jonathan, son of Saul (ii Sam. 9:12). In the genealogical list of the tribe of Benjamin (i Chron. 8:34, 35; 9:40, 41) he is called Micah (Heb. מִיכָה). Thanks to *Jonathan, his grandfather, and Mephi-Bosheth, his father, Mica no doubt benefited from David's generosity (ii Sam. 9:12; cf. 19:24–29).

For his descendants, see *Benjamin.

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mica † small plate of talc, etc.; mineral consisting essentially of silicate of aluminium occurring in glittering scales or in crystals. XVIII. — L. mīca grain, crumb; the use in min. was prob. orig. contextual (‘a particle’ of … ); perh. assoc. with L. micāre shine.
Hence micaceous XVIII.

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