Mineralogical transformations accompanying the chemical weathering of clay-slates from New South Wales

Abstract

A study has been made of the mineralogical transformations that have accompanied the chemical weathering of some Palaeozoic clay-slates from New South Wales. The weathered sequences occur within a limited range of climatic and topographical conditions. Chlorite, interlayered with other expanded-lattice silicate minerals, is the least chemically stable of the primary constituents. Montmorillonite is a little more resistant to the percolating waters, whereas illite, present in all primary materials as the 2M₁ polymorph, is relatively chemically stable. In the zone of maximum leaching, however, partial degradation and loss of illite is apparent. Kaolinite is the end-product of the breakdown of these clay minerals.