Bonding in silicates: an assessment of bonding in orthopyroxene |
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Authors: | RK ONions DGW Smith |
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Institution: | Department of Geology and Mineralogy, Parks Road, Oxford, England;Department of Mineralogy and Petrology, Downing Place, Cambridge, England |
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Abstract: | The molecular orbital and crystal field theories are compared and their applicabilities to bonding in silicates are discussed, A molecular orbital bonding model is favoured for orthopyroxene since bonding in both tetrahedral and non-tetrahedral sites within the crystal structure can be described and accommodated by the theory. It is suggested that Fe located in M2 sites has more electron delocalisation (or covalence) associated with it than Fe located in the M1 site. Order-disorder phenomena in orthopyroxene are discussed in relationship to Mueller's (1970) two-step exchange mechanism, whereby the first step corresponds to vacancy activation and the second step to exchange of Fe between an ‘octahedral’ site and a vacancy. |
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