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mica

(Science: chemical) The name of a group of minerals characterised 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 colour 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.

The important species of the mica group are: muscovite, common or potash mica, pale brown or green, often silvery, including damourite (also called hydromica); biotite, iron-magnesia mica, dark brown, green, or black; lepidomelane, iron, mica, black; phlogopite, magnesia mica, colourless, yellow, brown; lepidolite, lithia mica, rose-red, lilac. Mica (usually muscovite, also biotite) is an essential constituent of granite, gneiss, and mica slate; biotite is common in many eruptive rocks; phlogopite in crystalline limestone and serpentine. Mica diorite, a schistose rock, consisting of mica and quartz with, usually, some feldspar.

Origin: L. Mica crumb, grain, particle; cf. F. Mica.