mineral
Biotite (Mica)
K(Mg,Fe)3AlSi3O10(OH,F)2
Hardness: 2.5-3.0; Color: Dark brown to black; Luster: Vitreous to pearly; Structure: Monoclinic (platy/flaky); Cleavage: Perfect basal
- Hardness
- 2
- Color
- Dark brown to black
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 2.5-3.0; Color: Dark brown to black; Luster: Vitreous to pearly; Structure: Monoclinic (platy/flaky); Cleavage: Perfect basal
Formation & geological history
Formed in igneous rocks like granite and metamorphic rocks like schist through cooling magma or high-pressure alteration. Found throughout all geological eras.
Uses & applications
Used in the electronics industry as a thermal insulator, in building materials, and as a filler in paints and plastics.
Geological facts
It is often called 'black mica' and is part of a large group of sheet silicate minerals. It was named in honor of Jean-Baptiste Biot, a French physicist.
Field identification & locations
Identify in the field by its ability to peel into thin, flexible, transparent sheets. Extremely common in granite and gneiss worldwide.
More like this
Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
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
Epidote
Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)
mineral