| Biotite | |
|---|---|
 Thin tabular biotite aggregate (Image width: 2.5 mm) | |
| General | |
| Category | Darkmica series |
| Formula (repeatin unit) | K(Mg,Fe) 3(AlSi 3O 10)(F,OH) 2 |
| Creestal seestem | Monoclinic (2/m) Space Group: C 2/m |
| Identification | |
| Formula mass | 433.53 g |
| Colour | Mirk broun, greenish-broun, blackish-broun, yellae, white |
| Creestal habit | Massive tae platy |
| Twinnin | Common on the [310], less common on the {001} |
| Cleavage | Perfect on the {001} |
| Fractur | Micaceous |
| Tenacity | Brickle tae souple, elastic |
| Mohs scalehaurdness | 2.5–3.0 |
| Skinkle | Vitreous tae pearly |
| Streak | White |
| Diaphaneity | Skyre tae leamin tae opaque |
| Speceefic gravity | 2.7–3.1 |
| Density | 2.8–3.4 |
| Optical properties | Biaxial (-) |
| Refractive index | nα = 1.565–1.625 nβ = 1.605–1.675 nγ = 1.605–1.675 |
| Birefringence | δ = 0.03–0.07 |
| Pleochroism | Strong |
| Dispersion | r < v (Fe rich); r > v weak (Mg rich) |
| Ultravioletfluorescence | None |
| References | [1][2][3] |
Biotite is a commonphyllosilicatemeeneral athin themica group, wi the approximate chemical formulaK(Mg,Fe)
3AlSi
3O
10(F,OH)
2. Mair generally, it refers tae the dark mica series, primarily asolid-solution series atween the iron-endmemberannite, an the magnesium-endmemberphlogopite; mair aluminous endmembers includesiderophyllite. Biotite wis named biJ.F.L. Hausmann in 1847 in honour o the FrenchpheesicistJean-Baptiste Biot, who, in 1816, researched the optical properties omica, discovering mony unique properties.[4]
Biotite is a sheetsilicate.Airn,magnesium,aluminium,silicon,oxygen, anhydrogen furm sheets that are waikly boond thegither bipotassium ions. It is whiles cried "iron mica" acause it is mair airn-rich nor phlogopite. It is an aa whiles cried "black mica" as opponed tae "white mica" (muscovite) – baith furm in some rocks, in some instances side-bi-side.
