Muscovite.

Muscovite.

Muscovite is the most common form of mica. It is known as insinglass, potash mica, or common mica, and is a complicated hydrated phyllosilicate of aluminium and potassium. The basic formula is KAl2(AlSi3O10)(F,OH)2  The very thinly laminated structure of mica, is very obvious in this specimen, which has been collected from Two waters, Liskeard, East Cornwall.