Calcium sulpho - aluminate (Ettringite) can form on line stabilization of smectite soils containing sulphates and it is known to cause harmful effects to foundations. To examine the effect of line treatment on sulphate containing smectites a study was carried out on commercial bentonite from Rajasthan, India using a fixed percentage of sulphates of sodium, potassium, magnesium and aluminum prior to line treatment. The plasticity characteristics and X-ray diffraction patterns were obtained for all treatments. The study showed that no ettringite was formed in these cases but calcium aluminum silicate hydrate (3.35 angstroms0) was formed in all cases of line treatment in sulphate containing calcium bentonite. Evidence of occurrence of calcium aluminum silicate hydrate from a natural soil sample in Madras, India was observed close to a sample containing smectite and sulphate. This occurrence leads to the view that smectities can undergo modification to calcium aluminum silcate hydrates by diagenesis. The addition of barium chloride prevents the formation of this compound.