Biotite Mica in Matrix, from USA (No.143)

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Biotite Mica in Matrix, from USA (No.143)Biotite Mica in Matrix, from USA

Measurements Approx.
Height - 5.1 cm
Width - 5.7 cm
Length - 8.5 cm


Biotite is a common phyllosilicate mineral within the mica group. 

Biotite was named by J.F.L Hausmann in 1847 in honour of the French physicist Jean-Baptiste Biot, who, in 1816, researched the optical properties of mica, discovering many properties.

Biotite is a sheet silicate. Iron, magnesium, aluminium, silicon, oxygen, and hydrogen form sheets that are weakly bound together by potassium ions. It is sometimes called "iron mica" because it is more iron-rich than phlogopite. It is also sometimes called "black mica" as opposed to "white mica" (muscovite) – both form in some rocks, and in some instances side-by-side.


Biotite is found in a wide variety of igneous and metamorphic rock. For instance, biotite occurs in the lava of Mount Vesuvius and in the Monzoni intrusive complex of the western Dolomites. It is an essential phenocryst in some varieties of lamprohyre. Biotite is occasionally found in large cleavable crystals, especially in pegmatite veins, as in New England, Virginia and North Carolina. Other notable occurrences include Bancroft and Sudbury, Ontario. It is an essential constituent of many metamorphic schists, and it forms in suitable compositions over a wide range of pressure and temperature. It has been estimated that biotite comprises up to 7% of the exposed continental crust.

The largest documented single crystals of biotite were approximately 7 m2 (75 sq ft) sheets found in Iveland, Norway.

Biotite is said to may assist restructuring disorganised cell patterns. It is traditionally used to heal eyes and growths and to regulate bile.