The transformation of feldspars and muscovite to clay minerals in (Ca,Mg)-carbonate bearing hydrothermal media

Abstract

Experimental transformations of feldspars and muscovites following additions of magnesite and dolomite have been studied at PH₂O = 1 kbar, T = 200–600°C. Formation of layer silicates such as smectite, 7 Å (Mg,Al)-serpentine, some mixed-layer phases and other minerals is shown to be a function of the composition of the starting materials, temperature and run duration. It is established that 1 M- and 2 M₁-phlogopites are formed from 1 M- and 2 M₁-muscovites, respectively, under Mg-bearing hydrothermal conditions. Some causes of variations in the composition of 7 Å (Mg,Al)-serpentines at elevated temperature as a function of the composition of hydrothermal media are given. These data may be used to explain the main characteristics of clay mineral formation from feldspar- and muscovite-bearing sedimentary rocks during their alteration in postdiagenetic and metasomatic processes.