Muscovite – KAl₂(OH)₂Si₃AlO₁₀

(a) The structure of 2:1 clay minerals such as muscovite mica KAl₂(OH)₂Si₃AlO₁₀, in which K⁺ resides between the charged layers (exchangeable cation sites), Si⁴⁺ resides in sites of coordination number 4, and Al³⁺ in sites of coordination number 6.
(b) The polyhedral representation. In talc, Mg²⁺ ions occupy the octahedral sites and O atoms on the top and bottom are replaced by OH groups and the K⁺ sites are vacant.