Abstract

Cerium L3 absorption edge (L3-edge) X-ray absorption near edge structure (XANES) spectra were obtained from ~7 × 5 μm areas on green titanite and brown titanite (both with total Ce ~ 0.6 wt%) using the X-ray microprobe at the Pacific Northwest Consortium–X-ray Science Division (PNC-XSD) Insertion Device (ID) line of the Advanced Photon Source (APS). Using a wavelength-dispersive X-ray (WDX) fluorescence detector with a bent LiF (220) crystal monochromator (EE ~ 1000), we have overcome the challenge of having to measure trace amounts of Ce in a Ti-rich sample of which the energy of the fluorescence X-rays from Ce L3-edge and Ti K-edge excitation cannot be resolved with solid-state detectors. We show that both Ce3+ and Ce4+ are present in our titanite samples by examining the Ce L3-edge XANES spectra.

Our results show that to correctly determine trace element substitution mechanisms in titanite (and other minerals), it is necessary to determine multivalent element concentrations, including Ce3+/Ce4+. We present a new approach for predicting and evaluating multivalent trace element substitution in titanite and other minerals.

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