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 is a dark, flaky mica mineral, typically black or dark brown, forming platy crystals with a vitreous to pearly luster.
Biotite Physical Properties
Mohs Hardness
2.5Crystal System
monoclinicLuster
vitreousStreak Color
white to grayishCleavage
perfect basal (one direction)Fracture
unevenSpecific Gravity
2.7Colors
black, dark brown, dark greenTransparency
translucentType Locality
Ruggles Pegmatite Mine, New Hampshire, USAMineral Group
SilicatesUses
geological dating, mineral specimensAssociated Minerals
muscovite, quartz, feldsparRarity
commonGeological Context
It is a common rock-forming mineral found in a wide range of igneous rocks, such as granite and pegmatite, and metamorphic rocks like gneiss and schist.
