Image: <a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a> (CC BY 2.0)
monocliniccommonSilicates
Biotite
K(Mg,Fe)₃AlSi₃O₁₀(OH)₂
Biotite appears as dark, often black, flaky or platy crystals, typically with a shiny, somewhat pearly luster on its cleavage surfaces. It is often found in aggregates of stacked sheets.
Biotite Physical Properties
Mohs Hardness
2.5Crystal System
monoclinicLuster
vitreousStreak Color
white to grayishCleavage
perfect basal cleavage in one directionFracture
unevenSpecific Gravity
2.8Colors
black, dark brown, dark greenTransparency
translucentType Locality
Ruggles Pegmatite Mine, New Hampshire, USAMineral Group
SilicatesUses
industrial filler, insulation, geological indicator, collectorAssociated Minerals
muscovite, quartz, feldsparRarity
commonGeological Context
Biotite is a common rock-forming mineral found in a wide range of igneous rocks, such as granites and pegmatites, and metamorphic rocks like schists and gneisses. It forms during the cooling of magma or through the recrystallization of existing rocks under heat and pressure.
