\Mi"ca\, n. [L. mica crumb, grain, particle; cf. F. mica.]
(Min.)
The name of a group of minerals characterized by highly
perfect cleavage, so that they readily separate into very
thin leaves, more or less elastic. They differ widely in
composition, and vary in color from pale brown or yellow to
green or black. The transparent forms are used in lanterns,
the doors of stoves, etc., being popularly called
{isinglass}. Formerly called also {cat-silver}, and
{glimmer}.
Note: The important species of the mica group are:
      {muscovite}, common or potash mica, pale brown or
      green, often silvery, including {damourite} (also
      called {hydromica}); {biotite}, iron-magnesia mica,
      dark brown, green, or black; {lepidomelane}, iron,
      mica, black; {phlogopite}, magnesia mica, colorless,
      yellow, brown; {lepidolite}, lithia mica, rose-red,
      lilac. Mica (usually muscovite, also biotite) is an
      essential constituent of granite, gneiss, and mica
      slate; {biotite} is common in many eruptive rocks;
      {phlogopite} in crystalline limestone and serpentine.
{Mica diorite} (Min.), an eruptive rock allied to diorite but
   containing mica (biotite) instead of hornblende.
{Mica powder}, a kind of dynamite containing fine scales of
   mica.
{Mica schist}, {Mica slate} (Geol.), a schistose rock,
   consisting of mica and quartz with, usually, some
   feldspar.