Mystery of the Libyan desert glasses

High and low temperature and terrestrial and extraterrestrial origins have been proposed for the formation of Libyan desert glass (LDG). This paper reports results on the homogeneity of this mysterious material on a macro‐, micro‐ and nanometre scale and on its thermal expansion from −200 to 1500°C. A comparison with commercial SiO₂ glasses and some noncrystalline silicate varieties such as opal, agate and flint displays a similarity between LDG and the high temperature prepared SiO₂ glasses, whereas no similarity between LDG and the low temperature formed natural SiO₂ materials is present. New x‐ray diffraction results show equally that the intermediate range structures of LDG and high temperature prepared silica glasses are similar and that there is no similarity to those of opals (old gels) and silica gels (fresh gels). All published experimental findings are consistent with the hypothesis that LDG resulted from the fusion of a terrestrial material probably by the impact of an extraterrestrial body such as a comet or a meteorite. A low temperature sol‐gel like origin seems to be unlikely.