Mg
Al
Si
O
H
H2O

Vermiculite

Vermiculite, Mg3(Al,Si)4O10(OH)2 ยท 4H2O, has a monoclinic crystal system with a platy habit. It is an expanding clay.

Shirozu, H., and S.W. Bailey. 1966. Crystal structure of a two-layer Mg-vermiculite. American Mineralogist. 51:1124-1143.