Abstract
Spectrometries (Raman Laser microprobe, visible spectrometry and microreflectrometry) have been applied to the crystallochemical calibration of members of the Mg(Al,Cr)2O4 series, synthesized by melting in a solar furnace, then analyzed with an electron microprobe and by X-ray diffraction. This study shows that octahedral sites of Cr3+ are more and more distorted when Cr replaces progressively Al, leading possibly to a lowering of the lattice symmetry from O7h, to T2d. The stabilization energy of Cr decreases and the covalent factor increases with the substitution Al → Cr. Two spectral signatures have been shown on polished sections for Cr3+ in the chromite series. First, the reflectance at 600 nm increases linearly from 7 to 12 % with the Cr content increasing. Secondly, the location of the high frequency Raman band varies from 760 cm-1 for the Al-rich end member to 680 cm-1 for the Cr-rich end member, on synthetic members of the quaternay system (Mg,Fe) (Al,Cr)2O4 as well as on natural chromites of different compositions.
Published Version
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