mineral

Biotite (Black Mica)

Biotite - K(Mg,Fe)3(AlSi3O10)(OH)2

Hardness: 2.5–3.0 Mohs; Color: Black, dark green, or dark brown; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal (peels into thin sheets); Specific Gravity: 2.7–3.3

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

Identified February 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily in igneous and metamorphic rocks through high-temperature and pressure environments. Common in granite, schist, and gneiss; found across most geological eras where tectonic activity occurs.

Uses & applications

Used in industry as a filler in paints and plastics, as a lubricant, and in the manufacturing of rubber. Occasionally used as a mineral specimen for educational purposes, though less common in jewelry due to its fragility.

Geological facts

Biotite is known as 'black mica' and is a common component of the rock cycle. It is often used by scientists for potassium-argon dating of rocks because it contains high levels of potassium.

Field identification & locations

Identify in the field by its black color and ability to peel into flexible, elastic flakes with a fingernail. Found worldwide, particularly in mountainous regions containing granite and metamorphic basement rocks.

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Arenite (SiO2 based)

sedimentary

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Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

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Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

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