mineral

Biotite

K(Mg,Fe)_3AlSi_3O_10(OH,F)_2

Mohs hardness of 2.5 to 3; dark green, brown, or black color; pearly to submetallic luster; monoclinic crystal system with perfect basal cleavage.

Identified November 2, 2026More mineral →

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Physical properties

Mohs hardness of 2.5 to 3; dark green, brown, or black color; pearly to submetallic luster; monoclinic crystal system with perfect basal cleavage.

Forms in igneous and metamorphic rocks, such as granites, gneisses, and schists, through crystallization from magma or high-temperature alteration.

Used primarily as an industrial filler, in paints, and as a mineral specimen for educational and geological study.

Biotite is commonly known as 'black mica' and is part of the phyllosilicate mineral group.

Easily identified by its dark color and extreme flexibility into thin, elastic sheets; found worldwide in granitic pegmatites.

Gneiss or Schist

Gneiss or Mica Schist with Garnet

Limonite

FeO(OH)•nH2O

Limonite

FeO(OH)•nH2O

Limonite

FeO(OH)•nH2O

Limonite

FeO(OH)•nH2O

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)