The Collaborative International Dictionary of English v.0.48:

Heulandite \Heu"land*ite\, n. [After Heuland, an English
   mineralogist.] (Min.)
   A mineral of the Zeolite family, often occurring in
   amygdaloid, in foliated masses, and also in monoclinic
   crystals with pearly luster on the cleavage face. It is a
   hydrous silicate of alumina and lime.
   [1913 Webster]

WordNet (r) 3.0 (2006):

heulandite
    n 1: a group of minerals of the zeolite family consisting of a
         hydrous aluminum silicate of sodium and calcium