Structure of Cu-bearing orthopyroxene, Mg(Cu.56,Mg.44)Si2O6, and behavior of Cu2+ in the orthopyroxene structure |
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| Authors: | T Tachi H Horiuchi H Nagasawa |
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| Institution: | (1) Department of Chemistry, Gakushuin University, Mejiro 1-5–1, Toshima-ku, Tokyo l7l,;(2) Mineralogical Institute, Faculty of Science, University of Tokyo, Hongo 7-3–1, Bunkyo-ku, Tokyo 113, Japan, JP |
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| Abstract: | Cu-bearing pyroxene, Mg(Cu.56,Mg.44)Si2O6, has been synthesized by a flux method and crystal structure refinement has been performed by single crystal X-ray diffraction. It is found that the crystal structure is orthorhombic (space group Pbca) with unit cell dimensions of a=18.221(4), b=8.890(1), c=5.2260(7)Å and the cell volume of 846.5( )3Å3. In the M2-site one of the M-O bonds(M-O3B) is extremely expanded from 2.444(2) in enstatite to 2.732(2), thus the coordination polyhedron around M2-site is regarded as square pyramidal rather than square planar or octahedral. It is also found that the M1-site in the pyroxene structure is occupied almost exclusively by Mg, while the M2-site is almost evenly occupied by Mg and Cu. The observed extreme site preference shown by Cu2+ is unusual among the divalent cations with similar ionic sizes. |
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| Keywords: | Cu2+-beearing orthopyroxene Orthopyroxene Crystal structure Jahn-Teller effect |
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