The Mineral Biotite (Mica)
biotite mineral

Biotite belongs to the mica group and is a  Common Phyllosilicate Mineral. In a wider perspective, it refers to the darker group of mica, mainly a chain of solid solution in between the Magnesium-Endmember Phlogopite and the Iron-Endmember Annite; Siderophyllite being a part of  most of the Aluminous Endmembers. In the year 1847 J. F. L. Hausmann named the mineral as Biotite in honor of Jean-Baptiste Biot, a French physicist. In the year 1816, he investigated the optical properties of mica, whereby, he discovered various peerless properties.

Chemical Formula

K (Mg, Fe) 3 (AlSi3O10) (F, OH) 2

Derivation Of Name

Biotite was named after Jean Baptiste Biot (1774 – 1864) the French physicist, who researched the optical properties of mica.


A major class of black mica minerals often identified in the metamorphic and igneous rocks is named as Biotite. These comprise of fluorophlogopite, siderophyllite, astronaut, unit, phlogopite, flourannite as well as many more. This  kind of mica possesses identical physical properties of Sheet Silicate Minerals,  but their chemical composition differs. We come across Biotite in various metamorphic and igneous rocks. For example, we find Biotite in the lava of the Mount Vesuvius and in the invasive, complex of Monzoni belonging to the western Dolomites.


This mineral Biotite is believed as a stone of life, and connects one to a higher esteem and aids in guiding our lives.  Biotite helps in promoting systematic and disciplined advances, and helps one to view problems wisely.


Sometimes, you can find Biotite as big crystals that you can cleave, especially occurring in the veins of Pebmatite, such as in Virginia, New England and Northern Carolina. Other prominent places where they occur are Sudbury, Bancroft and Ontario.


Similar to many other mica minerals, the basal cleavage of Biotite is  very true. Comprising of thin layers or of flexible sheets, they flake off easily. The crystal system is monoclinic and laminated to form prismatic crystals having clear Pinacoid Ending. The pseudohexagonal crystal is made up of two pinacoid faces and four prism faces.
As mentioned above, the name Biotite is applied to many black colored mica minerals, with varied chemical compositions and identical physical properties. Other than by an analysis conducted in the Laboratory, there is no other means of differentiating one mineral from the other.

Color Deep brown, black, black with reddish tint, deep green. Minerals belonging to separate groups are Eastonite and Phlogopite with pale colors

Density 2.8–3.4 g/cm

Mohs scale hardness    2.5–3.0

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