Biotite

One calls biotite all Phyllosilicate of the family of the Mica S of composition intermediate between the Phlogopite KMg3AlSi3O10 (OH, F, Cl) 2 and the Annite KFe3AlSi3O10 (OH, F, Cl) 2. Often it also contains other cations like Titane and Manganèse.

Of color brown with black, it is one of the main components of the Granite S, of the Gneiss and of the Micaschiste S. Its Altération transforms it into Chlorite.

Biotite gives several polytypes to the number of variable layers. Symmetry depends on the stacking of the layers in each polytype. The most common polytypes are 1 M (monoclinical), 2 M 1 (monoclinical) and 3 T (trigonal).

The biotite name comes from Jean-Baptiste Biot, physicist French.

Deteriorations

Biotite is hydrated in Vermiculite or Chlorite, often with Ti remainder in the form of microcrystals of Rutile.

Layers

Biotite is one of minerals constituting of the plutonic rocks (Granite S, Diorite S, Syénite S, especially in the calc-alkali intermediate families), of the metamorphic rocks (Schiste S, Gneiss and Micaschiste S), and more rarely in the volcanic rocks (Ryolite S, Dacite S, Trachyte S, Andésite S).

  • largest biotite is a blade of cleavage of 2,5 X 1,5 m found in the mines of Purdey in Ontario with the Canada

  • Monts Ilmen in Russia
  • Evjö in Scandinavia
  • most beautiful alpine biotites are in the Val di Fassa in Italy

See too

Related article

Reference for the nomenclature

  • Rieder, Mr., Cavazzini, G., Of yakonov, Yu.S., Frank-Kamenetskii, V.A., Gottardi, G., Guggenheim, S., Koval', statement, Müller. G., Neiva, A.M.R., Radoslowich, E.W., Robert, J.L., Sassi, F.P., Takeda, H., Weiss, Z. and Wones. D.R.: Nomenclature off the micas . Canadian Mineralogist, 36 (1998), 905-912.

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