The Collaborative International Dictionary of English v.0.48:

Wollastonite \Wol"las*ton*ite\, n. [After Dr. W. H. Wollaston,
   an English chemist, who died in 1828.] (Min.)
   A silicate of lime of a white to gray, red, or yellow color,
   occurring generally in cleavable masses, rarely in tabular
   crystals; tabular spar.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wollastonite
    n 1: a white or greyish mineral typically found in metamorphic
         limestone; a silicate of calcium