Quartz and Feldspar Glasses Produced by Natural and Experimental Shock

Refractive index, density and infrared absorption studies of naturally and experimentally shocked‐produced glasses formed from quartz, plagioclase, and alkali‐feldspar confirm the existence of two main groups of amorphous forms of the framework silicates: solid‐state and liquid‐state glasses. These were apparently formed as metastable release products of high‐pressure‐phases above and below the glass transition temperatures. Solid‐state glasses exhibit a series of structural states with increasing disorder caused by increasing shock pressures and temperatures. They gradually merge into the structural state of fused minerals similar to that of synthetic glasses quenched from a melt. Shock‐fused alkali feldspars can, however, be distinguished from their laboratory‐fused counterparts by infrared absorption and by higher density. It is concluded from recovery shock experiments on single crystals that solid‐state glasses are formed by shock pressures between about 300 and 450 kb (feldspars) and 350 and 500 kb (quartz), whereas pressures exceeding some 430 kb (feldspars) and 500 kb (quartz) are necessary to produce liquid‐state glasses