MIAVA, A town of the County of Nentra, Il(mrary, on the Aliava Giver. GO miles northeast of Vienna (Map: Hungary. E 2). The ?manufacture of woolen and linen goods and bag ging is the chief industry. Population in 1900, 10.639.
MICA (Neo-Lat., from bat. micarc. to flash; confused with and influenced by mica, crumb). A group of mineral, that crystallize in the mono clinic system, and consist essentially of al num silicate with varying proportion- of potas sium, sodium, lithium. iron. magnesium. etc. The different speeies are characterized by a basal cleavage. yielding thin. tottoli scales that are colorless to jet black. The prinenial members of the group include the following: IluNcorite. or common called also potassium mica. as it is essentially an aluminum and potassium silicate. The colorless varieties of arc used in the doors of stoves and as lamp ehinineys. It is also employed as an insulation material. in wall-paper manufaeture. as in lubricant. and NvIwn ground it is used as an absorbent for glycerin 111 the manufacture of dynamite. During 1900 711,:i57 pound.: of sheet mica were mined in the United states. or sodium mica, is similar to the foregoing, e•xeept that the ,odium replaces the potassium in its It is of a yellowish to greenish color, /./pido/i(e, or lithium nmic•a, is a potassium. lithium. alumi nom silicate. also containing fluorine, is of a rose or peach-blossom color. It finds some use for
ornamental purposes, and is a source of lithium salts. Zinn/rah/it(' is of a complex composition, containing iron in addition to the potassium, lithium. and aluminum silicates. In color it is of a pale violet or yellow to brown and dark gray. Biotite, or magnesium iron mica, is a magnesium. potassium, and iron silicate. It is usually dark-colored, as green, brown, or black. Phloyopite is also a magnesium mien, generally nearly free from iren, and usually containing some fluorine. It is dark in color, being yellow ish-brown to brownish-red. Lepidomelanc is an iron mica generally black in color. The miens in crystalline rocks, muscovite being a normal constituent of granite, gneiss, and similar rocks. The deposits from which sheet mica is obtained are found in a coarse granite called pegmatite. The preparation of mica for the mar ket is comparatively simple. Tlit blocks, after being hoisted from the mine, are freed from ad hering rock, and then split by means of wedges or heavy knives. After this the mica is cut up into sizes suitable for the market, usually in pound packages. The mica waste is utilized as described previously under Muscovite'. Consult the volumes of the Mineral Resources, United States Oeologicul Surrey (Washington, annual).