Water in tektites and impact glasses by Fourier-transformed infrared spectrometry

To improve the scarce data base of H2O content in tektites and impact glasses, we analyzed 26 tektites from all four strewn fields and 25 impact glass samples for their H2O content. We used the fourier-transformed infrared (FTIR) spectrometry method, which permits measurement of areas of similar to 40 mu m in diameter. Our results show that the tektites have H2O contents ranging from 0.002 to 0.030 wt% (average 0.014 +/- 0.008 wt%). Ivory Coast tektites have the lowest H2O abundances (0.002-0.003 wt%), and Muong Nong-type indochinites and some North American tektites having the highest contents (up to similar to 0.03 wt%). Impact glass samples (from the Zhamanshin, Aouelloul, and Rio Cuarto craters) yielded H2O contents of 0.008 to 0.13 wt% H2O. Typical impact glasses from the Aouelloul and Zhamanshin craters have low H2O contents (0.008 to 0.063 wt%). Libyan Desert Glasses and Rio Cuarto glasses have higher H2O contents (similar to 0.11 wt%). We also analyzed glasses of unknown origin (e.g., urengoites; glass fragments from Tikal), which showed very low H2O contents, in agreement with an origin by impact. Our data confirm that all tektites found on land have very low H2O contents (<0.03 wt% H2O), while impact glasses have slightly higher H2O contents. Both glass types are very dry compared to volcanic glasses. This study confirms that the low H2O contents (<0.05 wt%) of such glasses can be considered good evidence for an origin by impact.