Geochemical features of the kaolin deposits from Sardinia (Italy) and genetic implications

Seventy six samples of altered and fresh volcanic rocks collected from four major kaolin deposits of Sardinia have been studied for major- and trace-element geochemistry. Kaolinization generally led to Al2 O3 increase and release of alkalis, alkaline earths, most of Fe and SiO2. Besides kaolinite other alteration products are cristobalite, alunite, dickite, illite, montmorillonite and quartz. The geochemical features of the Sardinian kaolins are independent of the parentrocktype, and dependent, on the contrary, on the physical-chemical conditions of formation.