Biotite mica

Formula: K(Mg, Fe)3(Al, Fe)Si3O10(OH, F)2
Hardness: 2.5-3
Description: the Biotite mineral group has a monoclinic crystal system and a pearly lustre. Biotite is a very common form of mica most commonly found in intrusive igenous and metamorphic rocks. The crystals can form in thin sheets that can be peeled off as layers which are very transparent and flexible.
Specimen number: R22782