Source : Webster's Revised Unabridged Dictionary (1913)

Biotite \Bi"o*tite\, n. [From Biot, a French naturalist.] (Min.)
   Mica containing iron and magnesia, generally of a black or
   dark green color; -- a common constituent of crystalline
   rocks. See {Mica}.

Source : WordNet®

biotite
     n : dark brown to black mica found in igneous and metamorphic
         rock