'Vermiculite' definitions:

Definition of 'vermiculite'

noun

Any of a group of yellow or brown hydrous silicate minerals having a micaceous structure

From: GCIDE

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. [1913 Webster] Vermiculose