mineral
Biotite on Quartz
Biotite (K(Mg,Fe)3AlSi3O10(F,OH)2) and Quartz (SiO2)
AI-generated identification · may be incorrectBiotite: 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.
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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.
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Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Septarian Pebble
Septarian nodule / Concretion
sedimentary