The Collaborative International Dictionary of English v.0.48:

Diopside \Di*op"side\, n. [Gr. di- = di`s- twice + ? a sight,
   fr. the root of ? I shall see: cf. F. diopside.] (Min.)
   A crystallized variety of pyroxene, of a clear, grayish green
   color; mussite.
   [1913 Webster]