Webster’s Revised Unabridged Dictionary · 1913
Vermiculite
Ver·mic′u·lite (vẽr·mĭk′ū·līt), 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.