mineral
Biotite Mica
Biotite (K(Mg,Fe)3AlSi3O10(OH,F)2)
Hardness: 2.5-3.0 Mohs; Color: Dark brown, black, or dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal cleavage (easily splits into thin sheets).
- Hardness
- 2
- Color
- Dark brown, black, or dark green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 2.5-3.0 Mohs; Color: Dark brown, black, or dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal cleavage (easily splits into thin sheets).
Formation & geological history
Formed in a wide range of igneous and metamorphic conditions. It is common in granites, schists, and gneisses. Geological age varies based on the host rock formation.
Uses & applications
Used in the electronics industry as an insulator, in paints as a filler, and by collectors for mineral specimens.
Geological facts
Biotite is known as 'black mica' and is part of a solid-solution series between phlogopite and annite. It was named in honor of Jean-Baptiste Biot, a French physicist.
Field identification & locations
Identify by its dark color and the way it flakes into flexible, elastic thin sheets. It is very common worldwide in regions with continental crust.
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock
![Green Apatite on Albite (Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]) — mineral](https://media.rockidentification.com/2391a63f-fb20-47d5-af9a-2035851eb32e-thumbnail.jpg)
Green Apatite on Albite
Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]
mineral