From The Collaborative International Dictionary of English v.0.48 :
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.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
cassiterite
n 1: a hard heavy dark mineral that is the chief source of tin