Glass chemistry of tektites

Due to their chemical composition tektite glasses can be considered as rhyo litic glasses according to petrological nomenclature. In comparison with in dustrial glasses, the aluminum content of all igneous rocks is unusually hi gh. Tektite glasses are so-called "hard", peraluminous network glasses. The incorporation of Al, Mg, Ca, Fe, and alkaline elements into the glass stru cture is discussed from the perspective of glass-chemical experience with o bsidian glasses. From the point of view of glass technology, the difference s in the chemical composition of tektites and obsidians are relatively smal l. Despite this fact clear differences in some physical characteristics exi st. Measurements of the linear thermal expansion, the change in density aft er annealing, and micrographs confirm the different thermal history of obsi dian and tektite glasses. Also on this basis, a volcanic source for the tek tites can be excluded in all probability. The observed homogeneity of the g lass composition in the individual strewn or sub-strewn fields is the conse quence 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 re markable material properties, e.g. high chemical resistance, long-term stab ility against devitrification, very small water contents and high Fe2+/Fe3 ratios. (C) 2001 Elsevier Science Ltd. All rights reserved.