High temperature crystallization process into opalized tuff

Abstract

White opalized tuff from the locality “Strmoš”– Probištip, is dominantly consisted of amor­phous SiO₂ (over 90% mass), and a minor quantity of crystalline tridymite and quartz. Disordered structure of this material is consequence of its genesis. Fast transition from liquid to solid state enables existence of dominant amor­phous state. This is confirmed by X-ray analysis and optical transmission microscopy. Thermal treatment of the mate­rial at 1200^oC causes higher degree of structure stabilization – crystallization of tridymite. The basic mass remains in the same disordered amorphous state, while the process of crystallization extends only in the zones with higher order degree. At the same time minimal changes occurs in the porosity, resulting in insignificant decreasing of specific sur­face area.