Mica containing metal and magnesia generally speaking of a black or dark green shade a typical constituent of crystalline rocks See Mica
- darkish to black mica found in igneous and metamorphic rock
- Mica containing iron and magnesia, generally speaking of a black or dark-green shade; -- a typical constituent of crystalline stones. See Mica.
In the mica-schists of this group biotite or muscovite may be the principal mineral and often both are present in varying proportions; the mica has developed from the argillaceous matter of the original rock; in addition there is always quartz and sometimes felspar (albite or oligoclase).