Fact Sheet:
– Chemical Composition: K(Mg,Fe)₃(AlSi₃O₁₀)(F,OH)₂
– Hardness: 2.5 to 3 on the Mohs scale
– Crystal System: Monoclinic
– Color Varieties: Black, dark brown, dark green
– Major Localities: Russia, Canada, the United States, and Brazil
– Common Uses: Electrical insulator, soil additive, petrologic study

Introduction: Biotite is a common phyllosilicate mineral within the mica group, characterized by its dark coloration and sheet-like crystal structure. It is named after the French physicist Jean-Baptiste Biot, who made significant contributions to the study of the optical properties of mica.

Formation: Biotite forms in a variety of geological environments, including igneous, metamorphic, and sedimentary rocks. It typically crystallizes from magmas and is a major component of granites and other intrusive rocks. Biotite also occurs in metamorphic rocks such as schist and gneiss, where it forms under high-temperature and pressure conditions.

Types and Colors: Biotite is typically black or dark brown, though it can appear dark green when iron content is lower. The mineral’s sheets can exhibit a metallic to glassy luster, and it is known for its perfect basal cleavage, allowing it to be split into thin, flexible layers.

Localities and Mining: Significant biotite deposits are found in Russia, Canada, the United States (notably in New England states), and Brazil. While biotite is widespread and commonly found in various geological formations, it is not typically mined for industrial use. Instead, it is often extracted incidentally during the mining of other minerals.

Applications:
Biotite has several practical applications:
– Electrical Insulator: Due to its resistance to heat and electricity, biotite is used as an insulator in electrical equipment.
– Soil Additive: Biotite can be ground into a powder and added to soils to improve potassium content and enhance plant growth.
– Petrologic Study: In geology, biotite is studied to understand the history and conditions of rock formation. It is also used to date rocks through radiometric methods.

Sources and further reading
https://mineralseducationcoalition.org/minerals-database/biotite/
https://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=214329