Resistance of natural glass

Abstract

Natural glass is a well-known phenomenon found in different geological formations on both the earth and the lunar surface. This demonstrates that the vitreous state has been resistant to change on these surfaces for more than a hundred million years. Glass formation is determined by magmatic, metamorphic and sedimentary processes. The quantities of naturally produced glass vary between 10^-6 and 10^9 g, and the occurrence is given in microscopie glassy inclusions as well as in 'glassy mountains'. The chemical composition of natural glass is mainly rhyolitic and peraluminous. Industrially produced glass usually contains less AI2O3 (< 10 wt%) than glass found in its natural state. The transformation of the glassy state occurs in different processes (in many cases at constant volume): crystallization ('devitrification'), solution (corrosion), or hydratization and pallagonitization. By these processes, glass is transformed into sheet silicates, zeolithes, feldspars etc. and amorphous gels of silicon, iron, manganese etc. Natural glass has been under consideration for use as a suitable material for isolating complex and dangerous wastes. To help solve problems of waste management particular to industrial production, and to achieve a greater productive use of natural glass resources, glass scientists and engineers as well as geoscientists will have to cooperate in the future.