This mineral is found in an ahnost pure state, forming a layer 1–2 m. thick at an average depth of about 50 m. beneath ground level, on the northern slope of the Monteti near to Capelbio (Orbetello, Tuscany). Above the layer of micaceous mineral there is developed a series of clays containing halloysite, metahalloysite, montmorillonite and kaolinite, locally rich in iron and manganese hydroxides. The series is quaternary, and lies on top of phyllites which have been attributed to the Permian. The whole series of clayey and ochreous minerals is of low-temperature hydrothermal origin, as I have shown in a recent communication (1948).