Structural Evolution of Quartz and Feldspar Crystals and their Glasses by Shock Compression

Abstract

The shock wave resulting from a meteorite impact may be considered one of the basic tenets for the Cretaceous/Tertiary extinction [1],[2]. We can find several impact craters on the present earth where we find shock-wave deformation textures and high-pressure minerals formed by shock-wave effects. Especially, stishovite is one of the best known shock products in nature [3]. Diaplectic glasses transformed from mineral crystals by shock metamorphism are also very interesting shock metamorphic materials. Tschermak [4],[5] observed high-density glass of plagioclase composition in the Shergotty basaltic achondrite and named it Maskelynite. The name diaplectic glass was also introduced for such amorphous materials from Ries crater by Chao [3] and Engelhart and Stoffler [6]. Initial investigations of natural diaplectic glasses from meteorites and meteorite crater rocks were begun by Duke [7], Bunch et al. [8], and Stoflfler [9]. They reported that diaplectic plagioclase glasses showed higher refractive index than fused plagioclase glasses. The natural diaplectic quartz glasses also show higher density or refractive index than those of fused SiO2 glass [10],[11]. However, the number of impact craters on the present earth and the amount of shock-wave-derived material that we can investigate are very limited because of the large erosion effects on the earth’s surface. Therefore, it is difficult to estimate the scale of impact pressure and shock effect correctly. On the other hand, shock compression experiments have been extensively carried out for various minerals [12],[13].