THE IMPACT ORIGIN OF LIBYAN DESERT GLASS

Libyan Desert Class (LDG) is a type of natural glass composed of nearl y pure silica (98 wt %). On the basis of this composition, a low-tempe rature process by precipitation from silica-rich water has been sugges ted. Here we present results which contradict this hypothesis. First, the molecular structure studied by infrared spectrometry is characteri zed by the absence of OH ions, which are usually found in amorphous si lica produced at low temperature. Second, chemical analyses show that the glass is not homogeneous in composition, but shows local enrichmen ts of meteoritic elements with typical chondritic proportions. The onl y explanation for these observations is that Libyan Desert Class forme d in a meteorite impact on a silica-rich target. The absence of organi c remains and the occurrence of pure silica inclusions (lechatelierite ) are consistent with this explanation.