K
Al
Si
O
H
F

Muscovite

Muscovite, KAl2(AlSi3)O10(OH,F)2, has a monoclinic crystal system with a tabular habit. The octahedral layer is occupied by Al3+ and the mineral is therefore dioctahedral, since two-thirds of the octahedra are occupied. The source of the lattice charge is the presence of Al3+ in place of Si4+ in 1/4 of the tetrahedral sites. The interlayer potassium is neatly nested among 12 oxygens and 2 hydroxyl groups, half from each layer.

Distribution

Muscovite is a widely distributed mineral and is found in igneous rocks. It also occurs from the decomposition of feldspars.

Collins, D.R., and C.R.A. Catlow. 1992. Computer simulation of structures and cohesive properties of micas. American Mineralogist. 77:1172-1181.