Vermiculite is a base-exchange mineral with a high base exchange capacity. The exchangeable bases are Mg exclusively, cr Mg and Ca. Base exchange takes place readily without grinding the material. Upon replacing the naturally occurring exchangeable bases of vermiculite with Li, Na, K, NH4, Rb, Cs, Mg, Ca and Ba, the resulting samples were subjected to x-ray and differential thermal analysis and water loss was determined at various temperatures. The results showed that the kind of adsorbed cation determines the expansion of the lattice, its hydration properties and the shape of the differential thermal curve. The properties of K saturated vermiculite closely approximate these of biotite.

By leaching Gruner’s hydrobiotite with MgCl2 solution, K ions are replaced by Mg ions with the resulting conversion of hydrobiotite into vermiculite, and by prolonged treatment of biotite with MgCl2 solution, it was converted into a material closely resembling vermiculite.

The results of this investigation seem to justify the conclusion that the exchangeable bases of vermiculite occupy interlayer positions as do K ions in biotite, and that vermiculite is essentially a Mg or Mg plus Ca mica. A new formula for vermiculite with the exchangeable bases in interlayer positions is proposed.

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