Source : Webster's Revised Unabridged Dictionary (1913)

Cassiterite \Cas*sit"er*ite\, n. [Gr. ? tin.] (Min.)
   Native tin dioxide; tin stone; a mineral occurring in
   tetragonal crystals of reddish brown color, and brilliant
   adamantine luster; also massive, sometimes in compact forms
   with concentric fibrous structure resembling wood ({wood
   tin}), also in rolled fragments or pebbly ({Stream tin}). It
   is the chief source of metallic tin. See {Black tin}, under
   {Black}.

Source : WordNet®

cassiterite
     n : a hard heavy dark mineral that is the chief source of tin