In several recent papers the chemical constitution of the tektitest has been compared with that of terrestrial rocks, both igneous and sedimentary. The impression might be obtained from these papers that there are no systematic chemical differences between tektites and terrestrial rocks. In fact, however, there is a systematic tendency for the tektites to be deficient in volatile materials. Friedman has found that the gas content of tektites is less than 1 ppm. He also finds that the water content is lower than that of nearly all terrestrial materials; it is nearly always less than .02 percent. In the same way Mueller first pointed out that the alkalies are systematically low in the tektites as compared to the oxides of divalent metals. Loewinson-Lessing is stated to have found a systematic chemical difference depending both on the acidity coefficient and the ratio of monovalent to divalent oxides.