What is "cassiterite"

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.

n. (context mineral English) A generally black mineral, composed of tin oxide, SnO₂, which is an important ore of tin.

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

Cassiterite is a tin oxide mineral, SnO. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite has been the chief tin ore throughout ancient history and remains the most important source of tin today.