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CH3041
2 :1 CLAY STRUCTURES
Muscovite
 [KAl3Si3O10(OH)2]2 

(Illite a 2o mineral
  also has this structure)
•
Smectite
[M0(Al2)(Si4)O10(OH)2 ]2



eg.montmorillonite
K+x+y(Al2-xMgx) (Si4-yAly)O10(OH)2