Valence of titanium in extraterrestrial pyroxenes

Trivalent titanium has been positively identified by optical spectral measurements of a green calcic pyroxene from the meteorite that fell near Pueblo de Allende, Mexico, in 1969. The chemical analysis of this titanian pyroxene (Dowty and Clark, 1973) revealed it to be an iron-free subsilicic diopside (fas-saite) containing coexisting Ti3+ and Ti4+ ions and having the chemical formula Ca1.0lM 0.38,n3+0.34,n4+0.14Alo.87Sil.2606- 

The polarized spectra of the pyroxene from the Allende meteorite illustrated in fig. 4.2 (Mao and Bell, 1974a) consist of three broad bands centred near 480 nm (20,830 cm-1), 610 nm (16,390 cm-1) and 666 nm (15,000 cm-1). There has been much debate about assignments of these bands (Dowty and Clark, 1973  

Optical spectral measurements thus provide a method for detecting, and possibly estimating the proportions of, Ti3+ ions in minerals which is difficult to do 

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