Internal Structure of Smectite Group

This group has trioctahedral or dioctahedral t-o-t-c structure, in which each o-sheet is sandwiched between two inward-pointing t-sheets. In the o-sheet, four out of six apical anions of each octahedron are 0 A the remaining two are OH-. 

Both tetrahedral and octahedral cations are substituted by cations of lower charge. The charge imbalance thus produced is neutralised by a small number of interlayer cations like Ca or Na, but they don t occupy all the available vacant sites between two t-o-t layers. They are probably arranged in alternating chains of occupied and vacant sites (Deer et al., 1992). 

Most common clay mineral of this group is montmorillonite, the general chemical formula of which is given below  

It is to be noted here that it contains nH20, which must be differentiated from the OH . While the former occupies the interlayer spaces, the latter occurs 

Number ofHfi sheets (in between two t-o-t lasers) Basal spacing 0) 

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