Mica
Micas (/ˈmaɪkəz/ 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. 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.
| Mica | |
|---|---|
| General | |
| Category | Phyllosilicates |
| Formula (repeating unit) | AB2–3(X, Si)4O10(O, F, OH)2 |
| IMA symbol | Mca |
| Identification | |
| Color | purple, rosy, silver, gray (lepidolite); dark green, brown, black (biotite); yellowish-brown, green-white (phlogopite); colorless, transparent (muscovite) |
| Cleavage | Almost perfect |
| Fracture | flaky |
| Mohs scale hardness | 2.5–4 (lepidolite); 2.5–3 (biotite); 2.5–3 (phlogopite); 2–2.5 (muscovite) |
| Luster | pearly, vitreous |
| Streak | White, colorless |
| Specific gravity | 2.8–3.0 |
| Diagnostic features | cleavage |
| References | |
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 to add "shimmer" or "frost."