mica
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Mica. Credit: U.S.
Geological Survey
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Any of a group of common silicate minerals
composed of sheets of linked silicate (SiO4) tetrahedra, with
aluminum replacing silicon
to some extent, and containing cations and
hydroxyl groups between the layers. The
three main types are biotite, muscovite,
and lepidolite; others include chlorite
and glauconite. Micas occur widespread
in many igneous, metamorphic,
and sedimentary rocks, and weather to
clay minerals. They show perfect basal
cleavage, producing thin, flexible flakes
which are used as electrical insulators and as the dielectric
in capacitors; ground mica is used in
paints, inks, wallpaper, rubber, and waterproof coatings.
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• GEOLOGY
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