Roger Weller, geology instructor
firstname.lastname@example.org copyright 2010-R.Weller
muscovite and biotite
Muscovite is KAl3Si3O10(OH)2
Biotite is K(Mg,Fe)3AlSi3O10(OH)2
Muscovite (white mica) and biotite (black mica) are really two distinct minerals.
In this specimen both micas are present and there is no overlap in composition.
Photo is copyright free for non-commercial educational uses.
Just credit photo to R.Weller/Cochise College.