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 a group of chemically and physically related aluminum silicate minerals, common in igneous and metamorphic rocks, characteristically splitting into flexible sheets used in insulation and electrical equipment.