Various chemical formula are given for vermiculite. The general formula given below suggests a typical formula, which has been calculated from 65 vermiculite analyses.
(Na0,21, K0,39 Mg0,19 Ca0,13 6H2O) (Mg5 Fe+20,2 Fe+3 0,8) [Si5.5 Al2.5 O20] (OH)4 Where the components in the first set of parenthesis represent the ion-exchangeable layer, the components in the second set of parenthesis compose the cations of the octahedral layer, and the components within the brackets comprise the tetrahedral layer.