Properties
| Category | Phyllosilicate minerals |
|---|---|
| Formula | K(Mg,Fe)3(AlSi3O10)(F,OH)2 |
| Crystal system | Monoclinic |
| Color | Dark brown, greenish-brown, blackish-brown, yellow |
| Crystal habit | Massive to platy |
| Cleavage | Perfect on the {001} |
| Fracture | Micaceous |
| Tenacity | Brittle to flexible, elastic |
| Mohs scale hardness | 2.5–3.0 |
| Luster | Vitreous to pearly |
| Streak | White |
| Diaphaneity | Transparent to translucent to opaque |
| Specific gravity | 2.7–3.3 |
From the Wikipedia article
Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula K(Mg,Fe)3AlSi3O10(F,OH)2. It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more aluminous end-members include siderophyllite and eastonite. Biotite was regarded as a mineral species by the International Mineralogical Association until 1998, when its status was changed to a mineral group. The term biotite is still used to describe unanalysed dark micas in the field. Biotite was named by J.F.L. Hausmann in 1847 in honor of the French physicist Jean-Baptiste Biot, who performed early research into the many optical properties of mica.
Source
Source record: crystal-compendium/biotite/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Biotite — revision id 1377997466. Text and properties from Wikipedia, licensed CC BY-SA 4.0.