Mystery of the Libyan desert glasses

High and loll, temperature and terrestrial and extraterrestrial origins hav e been proposed for the formation of Libyan desert glass (LDG). This paper reports results oil the homogeneity of this mysterious material on a macro- , micro- and nanometre scale and on its thermal expansion from -200 to 1500 degreesC. A comparison with commercial SiO2 glasses and some noncrystallin e silicate varieties such as opal, agate and flint displays a similarity be tween LDG and the high temperature prepared SiO2, glasses, whereas no simil arity 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 s imilar and that there is no similarity to those of opals (old gels) and sil ica gels (fresh gels). All published experimental findings are consistent w ith the hypothesis that LDG resulted from the fusion of a terrestrial mater ial probably kv the impact of an extraterrestrial body such as a comet or a meteorite. A low temperature sol-gel like origin seems to be unlikely.