The Collaborative International Dictionary of English v.0.48:

Sphene \Sphene\, n. [F. sph[`e]ne, fr. Gr. sfh`n a wedge.]
   (Min.)
   A mineral found usually in thin, wedge-shaped crystals of a
   yellow or green to black color. It is a silicate of titanium
   and calcium; titanite.
   [1913 Webster]