Source : Webster's Revised Unabridged Dictionary (1913)

Hornblende \Horn"blende`\, n. [G., fr. horn horn + blende
   blende.] (Min.)
   The common black, or dark green or brown, variety of
   amphibole. (See {Amphibole}.) It belongs to the aluminous
   division of the species, and is also characterized by its
   containing considerable iron. Also used as a general term to
   include the whole species.

   {Hornblende schist} (Geol.), a hornblende rock of schistose
      structure.

Source : WordNet®

hornblende
     n : a green to black mineral of the amphibole group; consists of
         silicates of calcium and sodium and magnesium and iron