mineral

Biotite on Quartz

Biotite (K(Mg,Fe)3AlSi3O10(F,OH)2) and Quartz (SiO2)

Biotite: Hardness 2.5-3.0, black to dark brown, pearly to submetallic luster, monoclinic (basal cleavage into thin sheets). Quartz: Hardness 7.0, white/translucent, vitreous luster.

Identified June 16, 2026More mineral →

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Physical properties

Biotite: Hardness 2.5-3.0, black to dark brown, pearly to submetallic luster, monoclinic (basal cleavage into thin sheets). Quartz: Hardness 7.0, white/translucent, vitreous luster.

Formation & geological history

Formed in igneous or metamorphic environments, specifically associated with granitic pegmatites or medium to high-grade metamorphic rocks like schist or gneiss.

Uses & applications

Used as an insulating material in the electronics industry and as a filler in paints and rubber. Quartz is used in glassmaking and jewelry.

Geological facts

Biotite is known as 'Black Mica' and is part of the mica group; it can be peeled into thin, flexible, transparent sheets using only a fingernail.

Field identification & locations

Identify by its 'book-like' layering (books of mica) and shiny, platy cleavage. Commonly found in granitic outcrops globally.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

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)]

mineral