Published online by Cambridge University Press: 09 July 2018
The chemical composition and structural characteristics of clays from samples of eight Tuscan soils were investigated. Using simple selective dissolution method (successive boiling in 1 N HCl and 0·5 N NaOH) it was possible to distinguish two types of low charge dioctahedral vermiculite; one easily HCl soluble the other practically insoluble.
Structural formulae for the soluble type were calculated from the chemical analysis of the dissolved material; for the insoluble type it was possible to calculate only an 'average' structural formula which included the micaceous material.
Since the HCl soluble vermiculites show a high content of Fe and Mg, they can be considered either as alteration products of glauconites or biotites, or as a result of a synthesis, at least in soils derived from basic rocks which do not contain mica.
The aluminous insoluble type, present also in parent material, may be the result of an incomplete 'illitization' in a marine environment.