Mica

(mi'kah.) [From L. mico, to glitter.] (Min.) A mineral of a foliated structure, called also tale, glimmer, and Muscovy gla . It consists of a number of thin lam inæ adhering to each other; and has long been used as a substitute for gla , particularly in Ru ia. Its chief constituents are silica, alumina, potash, and oxide of iron. It is one of the substances which constitute granite.-Mica-schist is, next to gnei , one of the most abundant of the Metamorphic Rocks (q. v.). It consists of alternate layers of mica and quartz, but is sometimes composed almost entirely of the thin and shining plates or scales of mica, and from this it pa es by insensible gradations into clay-slate. [s. 598]