Abstract

A raspberry-red grossular from the Sierra de Cruces Range in the state of Coahuila in Mexico has been investigated. Electron-microprobe analysis and 57 Fe Mossbauer and UV/VIS spectroscopy were used in order to investigate the nature of the unusual red colour. The composition of the garnet is approximately (Ca (sub 2.94) Mg (sub 0.09) Mn (super 2+) (sub 0.10) ) (sub 3.13) (Al (sub 1.90) Fe (super 3+) (sub 0.05) Mn (super 3+) (sub 0.01) ) (sub 1.96) Si (sub 2.97) O 12 . The UV/VIS spectrum is characterised by an absorption envelope centred around 19,000 cm (super -1) in the green region, which can be fitted with two bands located at 19,503 and 17,302 cm (super -1) , originating from two spin-allowed dd-electron transitions. They result from the presence of Mn (super 3+) on the octahedral site of point symmetry 3.

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