Micas (/ˈmkəz/ MY-kəz) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin 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.[6] It is particularly prominent in many granites, pegmatites, and schists,[7] and "books" (large individual crystals) of mica several feet across have been found in some pegmatites.[8]

(repeating unit)
AB2–3(X, Si)4O10(O, F, OH)2
IMA symbolMca[1]
Colorpurple, rosy, silver, gray (lepidolite); dark green, brown, black (biotite); yellowish-brown, green-white (phlogopite); colorless, transparent (muscovite)
CleavageAlmost perfect
Mohs scale hardness2.5–4 (lepidolite); 2.5–3 (biotite); 2.5–3 (phlogopite); 2–2.5 (muscovite)
Lusterpearly, vitreous
StreakWhite, colorless
Specific gravity2.8–3.0
Diagnostic featurescleavage
Sheets of mica
Photomicrographs of a thin section containing phlogopite. In cross-polarized light on left, plane-polarized light on right.
Dark mica from eastern Ontario

Micas are used in products such as drywalls, paints, fillers, especially in parts for automobiles, roofing and shingles, as well as in electronics. The mineral is used in cosmetics and food[9] to add "shimmer" or "frost."

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