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Biotite identification and geology

A common dark-colored black to dark brown sheet silicate mineral of the mica group, with the generalized formula K Mg,Fe ₃ AlSi₃O₁₀ OH ₂. Biotite is an important rock-forming mineral found in a wide variety of igneous and metamorphic rocks, including granite, diorite, schist, and gneiss. It is characterized by perfect basal cleavage, elastic sheets, and a vitreous to submetallic luster on cleavage surfaces. Field: mineralogy. Example: Biotite crystals in a granite hand specimen appear as shiny, dark flakes that can be peeled into flexible, elastic sheets using a fingernail or knife blade.. Related terms: Muscovite, Mica, Sheet silicate, Cleavage.

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:41.970235+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Biotite mean in geology?
A common dark-colored black to dark brown sheet silicate mineral of the mica group, with the generalized formula K Mg,Fe ₃ AlSi₃O₁₀ OH ₂. Biotite is an important rock-forming mineral found in a wide variety of igneous and metamorphic rocks, including granite, diorite, schist, and gneiss. It is characterized by perfect basal cleavage, elastic sheets, and a vitreous to submetallic luster on cleavage surfaces.
What is an example of Biotite?
Biotite crystals in a granite hand specimen appear as shiny, dark flakes that can be peeled into flexible, elastic sheets using a fingernail or knife blade.
Which earth-science field uses the term Biotite?
Biotite is used in mineralogy.
Which terms are related to Biotite?
Related terms in this reference are Muscovite, Mica, Sheet silicate, Cleavage.

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