mineral

Biotite (Black Mica)

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

Hardness: 2.5–3 on Mohs scale; Color: Black, dark green, or dark brown; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets).

Hardness: 2
Color: Black, dark green, or dark brown
Luster: Vitreous to pearly

Identified May 7, 2026More mineral →

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Physical properties

Hardness: 2.5–3 on Mohs scale; Color: Black, dark green, or dark brown; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets).

Formation & geological history

Forms in a wide range of igneous and metamorphic environments. It is a common constituent in granite, diorite, and schists, typically forming at high temperatures and pressures.

Uses & applications

Primarily used in industry as an insulator in electrical equipment, as a lubricant, and in the manufacturing of rubber and paint products. It is also significant in scientific dating through argon-argon and potassium-argon methods.

Geological facts

Biotite was named in honor of the French physicist Jean-Baptiste Biot, who researched the optical properties of micas in the early 19th century.

Field identification & locations

Identify by its dark color and the way it flakes into thin, flexible, elastic sheets. Common in many igneous mountain ranges and metamorphic belts globally.