Abstract

Ten chromian chlorites were examined by X-ray power diffraction and optical spectroscopic methods to determine the coordination of the chromium ion. The absorption spectra of all ten chlorites are essentially identical and are fully consistent with the presence of octahedrally coordinated chromium. There is no evidence for the presence of tetrahedrally coordinated chromium. These results are consistent with the high octahedral site preference energy of the Cr3+ ion. Application of determinative curves to the X-ray data yields total octahedral heavy atom contents that agree approximately with published chemical analyses if all heavy atoms are placed in octahedral sites rather than partitioned between octahedral and tetrahedral sites. The experimental data indicate appreciable segregation of heavy atoms into the interlayer octahedral sites.

Because of the small amounts of chromium involved and the absence of tetrahedral chromium, the author supports the view of Bayliss (1975) that the names kotschubeite and kammererite should be dropped. A “Cr”” or “chromian” prefix used with the currently accepted chlorite name appears adequate.

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