Pyroxenes omphacite

Ganguly (1973). Activity-composition relation of jadeite in omphacite pyroxenes Theoretical deductions. Earth Planet. Set Letters, 19 145-153. 

The Fe2+ —> Ti4 IVCT transition has been identified in the spectra of other titanian pyroxenes, including samples from the Moon (Bums et al., 1976 Dowty, 1978) and, perhaps, a blue titaniferous omphacite from Labrador (Curtis et al., 1975). An intense broad band in this omphacite centred around 15,000 cm-1 and showing a pressure-induced shift to lower energies was originally assigned to Fe2+ -> Fe3+ IVCT (Abu-Eid, 1976) but later it was reassigned as a Fe2+ - Ti4+ IVCT transition (Strens et al., 1982). 

Ca-Fe pyroxenes with compositions between hedenbergite and clinoferrosilite (Ca,Fe )(Fe )Si206 show structure in their spectra which requires more than two ferrous doublets for an adequate fit [214]. The observed subspectra may arise from the different numbers of iron and calcium neighbors on the three M3 sites. Even a more distinct structure is observed in the omphacites in which the distribution of the charges among the neighboring M2 sites (Ca " and Na" ) has a large effect on the Fe located in the Ml sites [215]. 

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