Glass chemistry of tektites

Due to their chemical composition tektite glasses can be considered as rhyolitic glasses according to petrological nomenclature. In comparison with industrial glasses, the aluminum content of all igneous rocks is unusually high. Tektite glasses are so-called “hard”, peraluminous network glasses. The incorporation of Al, Mg, Ca, Fe, and alkaline elements into the glass structure is discussed from the perspective of glass-chemical experience with obsidian glasses. From the point of view of glass technology, the differences in the chemical composition of tektites and obsidians are relatively small. Despite this fact clear differences in some physical characteristics exist. Measurements of the linear thermal expansion, the change in density after annealing, and micrographs confirm the different thermal history of obsidian and tektite glasses. Also on this basis, a volcanic source for the tektites can be excluded in all probability. The observed homogeneity of the glass composition in the individual strewn or sub-strewn fields is the consequence of an extreme formation process, e.g. the condensation from a plasma. So far there has been no technological experience with large-volume glass synthesis using a plasma jet. Tektites represent a natural product with remarkable material properties, e.g. high chemical resistance, long-term stability against devitrification, very small water contents and high Fe2+/Fe3+ ratios.