XANES study of titanium coordination in natural diopsidic pyroxenes
Quartieri, Simona; Antonioli, Gianni; Artioli, Gilberto; Lottici, Pier Paοlο
European Journal of Mineralogy Volume 5 Number 6 (1993), p. 1101 - 1110
published: Dec 1, 1993
manuscript accepted: Jun 25, 1993
manuscript received: Feb 2, 1993
ArtNo. ESP147050506018, Price: 29.00 €
Abstract A series of diopsidic pyroxenes having Si and Al deficiency in the tetrahedral sites were selected for an X-ray absorption near-edge study at the Ti and Fe K-edge using synchrotron radiation. The samples were previously characterized by single-crystal X-ray diffraction and the geometrical features were interpreted on the basis of Ti4+ → Si substitution. The analysis of the XANES spectral features confirms that Ti4+ preferentially enters the tetrahedral site in two of the diopsides (D3 and D13), characterized by the complete absence of Al3+. In the other three diopside samples (D38, D39, D102) Ti4+ appears to be distributed among the tetrahedral and the octahedral sites. The Fe K-edge spectra of the five pyroxenes do not show any evidence of tetrahedrally-coordinated iron; the energies of the XANES features, compared with those of the reference compounds, suggest that the prevalent oxidation state of iron in the diopsides investigated is 2+.