Mineral group · Mica group
Biotite
K(Mg,Fe)3(AlSi3O10)(OH)2 (series)
Biotite is the black to brown mica series (annite–phlogopite) of granites and schists; the IMA now treats 'biotite' as a series name rather than a species. Large books come from Ontario (Bancroft), Norway and Brazil. It is a reference specimen; the golden-brown magnesium end member phlogopite is more collectible.
| Formula | K(Mg,Fe)3(AlSi3O10)(OH)2 (series) |
|---|---|
| IMA status | group |
| Crystal system | Monoclinic |
| Mohs hardness | 2.5–3 |
| Group | Mica group |
| Type locality | None |
| Streak | White to grey |
| Specific gravity | 3.0 |
Elsewhere
- Wikidata: Q116451656
- Mindat: Biotite
- Wikipedia: Biotite
Cite this article
Stratum Study. "Biotite" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/biotite. Accessed 2026-09-20.
@misc{stratum-biotite,
title = {Biotite},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/minerals/biotite}},
year = {2026},
note = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.