Crystal-field spectra for blue and green diopsides synthesized in the join CaMgSi2O6-CaCrAlSiO6 |
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| Authors: | Ko Ikeda Kenzo Yagi |
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| Institution: | (1) Department of Mining and Mineral Engineering, Yamaguchi University, 755 Ube, Japan;(2) Hokusei Gakuen College, 061-01 Sapporo, Japan |
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| Abstract: | Synthetic diopsides in the join CaMgSi2O6 CaCrAlSiO6 have been studied by means of crystal-field theory. These diopsides are either blue or pale green in colour. The former forms at lower temperatures and the latter at higher temperatures. The optical spectra and colours can be unequivocally explained based on the assumption that Cr3+ions occupy both tetrahedral and octahedral sites in the diopsides. In the blue diopsides Cr3+ions are present in two kinds of spin state, i.e., tetrahedrally coordinated low spin and octahedrally coordinated high spin. On heating the blue diopsides, tetrahedral occupancy of chromium decreases sharply due to spin transformation from tetrahedral low spin to octahedral high spin. Above 1,160° C nearly all chromium ions are present in octahedral sites with high spin state and the diopsides become pale green in colour. Some petrogenetic applications of the resultes are discussed. |
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