Mica

Mica: mica (pronounced: mike-a) Mica is a silicate mineral composed of potassium (K), alluminum (Al), silicate (SiO). It breaks down into thin, flexible, shiny and often transparent sheets. Two of the most common varieties are dark mica, biotite and light mica, muscovite. Both of these minerals are very common in metamorphic rocks such as gneiss and schist, as well as in intrusive rocks like granite. Long sheets of mica usually occur in dikes (pegmatite) in connection with felsic batholiths.