Properties of Biotite

Biotite is a dark-colored mica mineral belonging to the phyllosilicate group. It is part of the larger mica mineral family, which also includes muscovite, phlogopite, and others. Biotite is typically black or dark brown and is characterized by its sheet-like structure.

Image of biotite mineral
Credit: James St. John, CC BY 2.0, via Wikimedia Commons

The following table provides a comprehensive list of biotite properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).

Note: click on the icon to switch between Metric and Imperial units.

Table of Biotite Properties
Physical Properties
Metric
Chemical FormulaK(Mg,Fe)3AlSi3O10(OH,F)2
Molar Mass433.53 g/mol
Crystal SystemMonoclinic
Mohs Hardness2.5 - 3
Density2700 - 3300 kg/m3
ColorDark brown, greenish brown, blackish brown, yellow, or white
DiaphaneityTransparent to opaque
LusterVitreous, pearly
Cleavage(001) perfect
FractureUneven, elastic
StreakWhite gray

Note: unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)

Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017.