Mica

The name of a group of minerals characterized by highly perfect cleavage, so that they readily separate into very thin leaves, more or less elastic. They differ widely in composition, and vary in color from pale brown or yellow to green or black. The transparent forms are used in lanterns, the doors of stoves, etc., being popularly called isinglass. Formerly called also cat-silver, and glimmer.

any of various minerals consisting of hydrous silicates of aluminum or potassium etc. that crystallize in forms that allow perfect cleavage into very thin leaves; used as dielectrics because of their resistance to electricity