Source : Webster's Revised Unabridged Dictionary (1913)

Vermiculite \Ver*mic"u*lite\, n. [L. vermiculus, dim. of vermis
   worm.] (Min.)
   A group of minerals having, a micaceous structure. They are
   hydrous silicates, derived generally from the alteration of
   some kind of mica. So called because the scales, when heated,
   open out into wormlike forms.