Polarized optical absorption spectra of synthetic chromium doped Mg2SiO4 (forsterite)

Abstract

Abstract. Polarized optical absorption measurements were carried out on three single crystals of Mg2SiO 4 (forsterite), differently doped with Cr. Two crystals containing average 0.013 and 0.027 weight% Cr, respectively, were pulled from the melt in air, whereas one crystal containing average 0.08 weight% Cr was pulled from the melt in an argon atmosphere. The absorption spectra of the three crystals agree with each other although the intensity of single absorption bands varies significantly. In all 7-polarized patterns a sharp absorption line around 18 000 cm-x (550 rim) appears. Conjectures are presented to assign this line to the lasing center in Cr doped forsterite which very likely exists as Cr a+ at the fourfold coordinated Si site.

Substitution and diffusion of Cr2+ and Cr3+ in synthetic forsterite and natural olivine at 1200–1500 °C and 1 bar

“…In addition, Cr 4+ may occur in tetrahedral coordination in synthetic olivine (e.g. Akhmetzyanov et al, 2013;Rager et al, 1991; Yen and Jia, 1995), and Cr 6+ is stable in olivine-bearing synthetic melts equilibrated at high oxygen fugacity (Berry and O'Neill, 2004). In melts, the transition between predominantly Cr 2+ and predominantly Cr 3+ occurs in the geologically-relevant region between the quartz-fayalite-magnetite and iron-wüstite equilibria (Berry and O'Neill, 2004;Berry et al, 2006).…”

A combined Fourier transform infrared and Cr K-edge X-ray absorption near-edge structure spectroscopy study of the substitution and diffusion of H in Cr-doped forsterite

“…Many nominally anhydrous minerals can contain H in trace amounts bonded to O on regular crystallographic sites to form O-H structural units (Libowitzky and Beran, 2006). From the perspective of chemical thermodynamics, this O-H substitution depends on the fugacity of H 2 O (f H 2 O; Kohlstedt et al, 1996;Padrón-Navarta and Hermann, 2017;Rauch and Keppler, 2002;Tollan et al, 2017;Withers et al, 2011), and this component has accordingly been called "water". In minerals including, but not limited to, olivine, orthopyroxene, clinopyroxene and garnet, H has been shown to diffuse extremely rapidly (Barth et al, 2019;Demouchy and Mackwell, 2003;Demouchy and Mackwell, 2006;Ferriss et al, 2016;Kohlstedt and Mackwell, 1998;Mackwell and Kohlstedt, 1990;Peslier et al, 2015;Reynes et al, 2018;Stalder and Skogby, 2003;Stalder et al, 2007;Sundvall et al, 2009).…”