A Mِssbauer effect study of Fe environments in impact glasses

A room temperature 57Fe Mössbauer effect investigation is reported for four impact glasses: Aouelloul glass, Darwin glass, an Irghizite and Wabar glass. Resulting spectra are suitably fit to two components using the two-dimensional extended Voigt-based fitting method. The present results show that the Fe environments in impact glasses show a well defined distribution of Fe oct 2 + sites similar to that seen in tektites with mean values of the center shift and quadrupole splitting of about +1.0 mm/s (relative to α-Fe) and 1.9 mm/s, respectively. However, unlike tektites there is no clearly defined Fe tet 2 + sites and no clear distinction, in general between Fe tet 2 + and Fe3+ sites. The non- Fe oct 2 + sites in impact glasses show both a broad distribution within each sample as well as considerable variation between samples. These features are characteristic of a wider range of pressures, temperatures and oxygen fugacities that were present during formation these materials. The clear differences between the Mössbauer spectra of impact glasses and tektites may form an effective method of distinguishing between these classes of materials.