Mica
Silicate · e.g. KAl₂(AlSi₃O₁₀)(OH)₂ · also: Muscovite, Biotite
Mica is a group of sheet silicates that split into thin, flexible, transparent flakes; muscovite is silvery and biotite is dark brown-black.
What is mica?
Micas are sheet-silicate minerals with one perfect cleavage, so they peel apart into thin, elastic, transparent sheets. Silvery muscovite and dark brown-black biotite are the common ones, both widespread in granites and schists. Large muscovite “books” were once used as furnace windows.
Properties
- Chemical formula
- e.g. KAl₂(AlSi₃O₁₀)(OH)₂
- Category
- Silicate
- Hardness (Mohs)
- 2–2.5
- Crystal system
- Monoclinic
- Lustre
- Pearly to vitreous
- Streak
- White
- Colour
- Silvery (muscovite), dark (biotite)
- Cleavage / fracture
- Perfect basal (one direction)
How to identify mica
- →Splits into thin, flexible, elastic sheets (perfect basal cleavage).
- →Silvery and transparent (muscovite) or dark brown-black (biotite).
- →Very soft, hardness 2–2.5.
- →Pearly, shimmering lustre on the sheets.
Where mica is found
Mica is common worldwide in granites and pegmatites, with large crystals from India, Brazil and the USA.
Mica finds on minShelf
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