Al coordination and local structure in minerals: XAFS determinations and multiple-scattering calculations for K-feldspars

¹ INFN - Laboratori Nazionali di Frascati, P.O. Box 13, 00044 Frascati, Italy
² Commissariat à l'Energie Atomique, DSM/DRECAM/SRSIM, Bâtiment 462, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
³ Dipartimento di Scienze Geologiche, Università di Roma Tre, Via Ostiense 169, I-00154 Roma, Italy
⁴ Dipartimento di Scienze della Terra, Università di Camerino, Via Gentile III da Varano, I-62032 Camerino, Italy
⁵ Dottorato in Scienze Mineralogiche e Petrologiche, Universitá di Firenze Via La Pira 4, I-50121 Firenze, Italy

Received: 24 January 1997
Accepted: 15 April 1997

Abstract

The Al K-edge spectra of three potassium feldspars : sanidine, microcline and orthoclase, all with four-fold–coordinated Al, have been measured by X-ray absorption near-edge structure spectroscopy and calculated according to the multiple-scattering formalism using clusters of different sizes and the exchange-correlation potential. Although these structures are quite complex, and clusters as large as containing ca. 150 atoms are needed to calculate them, a significant agreement has been obtained between experimental spectra and calculated ones up to 60 eV above the threshold, both for energy positions and for relative intensities. Moreover, while the gross features of all spectra appear to be dominated mainly by the first coordination sphere around the absorber, effects due to higher shells are detected.