Geological Glossary
Glossary of common terms used in geology, and related to earth sciences.
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Mica

Muscovite mica
Micas are another group of silicate minerals composed of varying amounts of potassium, magnesium, iron as well as aluminum, silicon and water.

All micas form flat, book-like crystals that peal apart into individual sheets on cleavage planes. Crystals cleave into smooth flakes. Biotite is dark, black or brown mica; muscovite, shown here, is light-colored or clear mica. Mica is so soft that you can scratch it with a fingernail.


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