mica

thumb|Sheets of mica thumb|Optical mineralogy|Photomicrographs of a thin section containing phlogopite. In cross-polarized light on the left, plane-polarized light on the right. thumb|Dark mica from eastern Ontario

Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into fragile elastic plates. This characteristic is described as perfect basal cleavage. Mica is common in igneous and metamorphic rock and is occasionally found as small flakes in sedimentary rock. It is particularly prominent in many granites, pegmatites, and schists, and "books" (large individual crystals) of mica several feet across have been found in some pegmatites.