Biotite
| Colour | Black, Brown |
|---|---|
| Mohs hardness | 2.5–3.0 |
| Lustre | Vitreous to pearly |
| Streak | White |
| Crystal system | Monoclinic |
| Transparency | Transparent to translucent to opaque |
| Cleavage | Perfect on the {001} |
| Fracture | Micaceous |
| Specific gravity | 2.7–3.3 |
What is Biotite?
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 hono
How to identify Biotite
- Lustre: Vitreous to pearly.
- Hardness: Mohs 2.5–3.0 — soft; a knife will scratch it.
- Streak: White.
- Habit: Monoclinic crystal system.
Biotite in different forms
Stones often confused with Biotite
Frequently asked questions
How hard is Biotite?
Biotite is Mohs 2.5–3.0 on the hardness scale.
What colour is Biotite?
Biotite is typically black, brown (Dark brown, greenish-brown, blackish-brown, yellow).