D defs.my
Entry 1 sense Webster, 1913

Biotite

/bī'-ət-ītˌ/ · Bi·o·tite · IPA /ˈbaɪəˌtaɪt/
01 n. Mica containing iron and magnesia, generally of a black or dark green color; -- a common constituent of crystalline rocks. See Mica.
  1. 1.
    Mica containing iron and magnesia, generally of a black or dark green color; -- a common constituent of crystalline rocks. See Mica.(Min.) See: Mica