mineral
Biotite Mica (or Tourmaline fragment)
K(Mg,Fe)3AlSi3O10(F,OH)2
AI-generated identification · may be incorrectHardness 2.5–3.0 Mohs, black to dark greenish-brown, vitreous to pearly luster, perfect basal cleavage producing thin sheets, monoclinic.
Identified More mineral →
Explore Biotite Mica (or Tourmaline fragment) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness 2.5–3.0 Mohs, black to dark greenish-brown, vitreous to pearly luster, perfect basal cleavage producing thin sheets, monoclinic.
Formation & geological history
Forms in igneous rocks (like granite and pegmatites) and regional metamorphic rocks under moderate-to-high pressure and temperature.
Uses & applications
Used primarily as an insulating material in electrical equipment, in joint compounds, and as a scientific indicator of thermal history.
Geological facts
Biotite was named in honor of French physicist Jean-Baptiste Biot, who discovered the unique optical properties of mica crystals.
Field identification & locations
Identified by its dark color, flexible flaky sheets, and glassy luster; widely found within granite outcrops and mica schists.
More like this
Other mineral specimens
Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Limonite
FeO(OH)•nH2O
mineral
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Feldspar
Feldspar Group (Tectosilicate, e.g., KAlSi3O8)
mineral
Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous