Characteristic of Fe in tektite observed from XANES and UV-Vis spectroscopy

Abstract

Abstract Tektite is a geological sample formed as a result of a collision of the meteorite on the surface. An energy from the collision results in an excavation of the melted material into the Earth’s atmosphere and landed back on the surface further away from the impact site having glassy or crystalline textures. Tektite was deposited in Thailand and was identified as part of the Australasian strewn field. Chemical compositions of tektites have previously been studied. However, there is no study has established a relationship between composition and color of tektites. Thus, this study aims to relate the characteristic of color-center element, Fe, to the color of tektites using X-ray Absorption Near Edge Structure (XANES) and UV-Vis spectroscopy. Nine tektite samples were collected from Korat plateau and purchased from Thailand and Vietnam gem markets. XANES spectra of all (nine) samples show similar Fe K-edge pattern with pre-edge and E0 at 7080-7089 and 7118 eV, respectively. The spectrum is 100 percent matched with XANES structure of FeO standard suggesting Fe component of Fe2+ oxidation state in the sample. Seven, out of nine, samples establish similar UV-Vis broad absorption peak at 492-539 nm, which corresponds to absorption peak of Fe2+. The UV-Vis absorption spectrum cannot be obtained from two samples possibly due to high Fe-content in the samples. The calculated energy band gaps (E g ) of the samples are in between 1.35 eV to 1.76 eV with maximum absorption in between 1.88 eV to 1.95 eV. The result is in consistent with a black color of the tektite. It indicates that cause of color in tektites is related to Fe-content and can be explained by the energy band. This study can be furthered compare with moldavite (green variety of tektite) in order to identify cause of color in impact-related materials like tektites, as well as to provide information for identification of synthetic and genuine moldavites and also for characterization of tektites sources using the component of various Fe oxidation states.