mineral
Biotite mica
Biotite, a potassium–iron–magnesium phyllosilicate mica; approximate formula K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂
AI-generated identification · may be incorrectDark brown to black with a vitreous-to-pearly luster and perfect basal cleavage, splitting into thin flexible sheets. Mohs hardness 2.5–3; monoclinic crystal structure. The specimen appears consistent with a mica-rich piece, though identification from the image alone is uncertain.
Identified More mineral →
Explore Biotite mica in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown to black with a vitreous-to-pearly luster and perfect basal cleavage, splitting into thin flexible sheets. Mohs hardness 2.5–3; monoclinic crystal structure. The specimen appears consistent with a mica-rich piece, though identification from the image alone is uncertain.
Formation & geological history
Biotite crystallizes in many igneous rocks and forms during metamorphism; it is common in granite, schist, and gneiss. Its formation spans a wide range of geological ages.
Uses & applications
Used mainly as a geological indicator and mineral specimen; ground mica has limited industrial uses as a filler and insulating material. Large attractive crystals may be collected or displayed.
Geological facts
Mica’s layered structure allows it to cleave into extremely thin sheets. Biotite is a common rock-forming mineral named for physicist Jean-Baptiste Biot.
Field identification & locations
Look for dark, shiny flakes that peel into thin sheets; it is commonly found in granites and metamorphic rocks worldwide. A close view of cleavage and a scratch test can help distinguish it from other dark minerals.
