XAFS study on the Zr local structures in tektites and natural glasses

Abstract

The local structures of tektites and natural glasses were studied by Zr K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements in order to obtain quantitative data on the Zr-O (bonding) distances and coordination numbers for the glasses. Zr4+ ions have different coordination environments. The structure of glass (tektite, impact-related glass, fulgurite, and volcanic glasses) is affected by the temperature during the glass-formation process. Differences in the formation processes for natural glasses result in different local structures for the zirconium ions. All tektites can be classified as being of the same type and as having 7-fold coordination Zr ions. The Zr-O distances in tektite glasses are 2.198-2.215 Å, and their XANES spectra are similar, too. Impact-related glasses can be classified into different types and are formed under different physical and geological processes at the impact event. Volcanic glasses, impact-related glasses, and fulgurite glasses have several local Zr structures with 6- and 7-fold coordinated Zr ions. It can thus be concluded that local structures of Zr in natural glasses are closely related to the formation temperature and quenching conditions of the glasses. The Zr XAFS spectra of natural glasses can be used to identify the naturalglasses.