The mica group of sheet silicate (phyllosilicate) minerals includes several closely related materials having close to perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.

The word "mica" is derived from the Latin word mica, meaning "a crumb", and probably influenced by micare, "to glitter".

Chemically, micas can be given the general formula

Structurally, micas can be classed as dioctahedral (Y = 4) and trioctahedral (Y = 6). If the X ion is K or Na, the mica is a "common" mica, whereas if the X ion is Ca, the mica is classed as a "brittle" mica.

Common micas:

Brittle micas:

Very fine-grained micas, which typically show more variation in ion and water content, are informally termed "clay micas". They include

Mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites.

Tat language may refer to the following: