Source : Webster's Revised Unabridged Dictionary (1913)

Natrolite \Na"tro*lite\ (?; 277), n. [Natron + -lite: cf. F.
   natrolithe.] (Min.)
   A zeolite occuring in groups of glassy acicular crystals, and
   in masses which often have a radiated structure. It is a
   hydrous silicate of alumina and soda.

Source : WordNet®

natrolite
     n : a group of minerals of the zeolite family consisting of a
         hydrous silicate of sodium and aluminum