Published online by Cambridge University Press: 14 March 2018
A genetic classification of clay rocks is given in which five main types are recognized. In this classification minerals of the kaolin group formed directly from hydrothermal solutions, along with sulphides, sulphates, and pneumatogenic minerals, are separated from the same minerals formed by the hydrothermal-metasomatic action of gases and vapours on aluminosilicate rocks. Some data on the occurrence of these two types in Azerbaijan are recorded. The origin of the bentonitic clays (“gilabi”) of Azerbaljan is also discussed; the geology of the deposits indicates cycles of volcanic activity and long-range transport of volcanic ash.