The Collaborative International Dictionary of English v.0.48:

Zoisite \Zois"ite\, n. [After its discoverer, Von Zois, an
   Austrian mineralogist.] (Min.)
   A grayish or whitish mineral occurring in orthorhombic,
   prismatic crystals, also in columnar masses. It is a silicate
   of alumina and lime, and is allied to epidote.
   [1913 Webster]