The crystal chemistry of the humite minerals; Fe (super 2+) -Ti (super 4+) charge transfer and structural allocation of Ti (super 4+) in chondrodite and clinohumite
The crystal chemistry of the humite minerals; Fe (super 2+) -Ti (super 4+) charge transfer and structural allocation of Ti (super 4+) in chondrodite and clinohumite (in 4th European conference on Mineralogy and spectroscopy, Georges Calas (president))
European Journal of Mineralogy (December 2002) 14 (6): 1027-1032
An XRD, EPMA and polarized electron absorption spectroscopy study is reported of two chondrodites and four clinohumites. The dominating features of all spectra are: 1) a slightly polarized absorption edge in the UV at energies > 35 000 cm (super -1) , 2) a strong, broad band at 23 300 cm (super -1) with band widths near 6000 cm (super -1) and strong polarization with E alpha and 3) a complex low energy band system at 11 600 cm (super -1) in E alpha , 9500 in E gamma and 7700 cm (super -1) in E beta (corresponding with the d-d bands in olivines caused by Fe (super 2+) in M1 and M2). These spectral properties explain colour and pleochroism (alpha golden yellow to orange, beta and gamma light yellow to almost colourless). The band energy is consistent with that expected for metal-metal charge transfer in Fe (super 2+) Ti (super 4+) pairs. The Ti (super 4+) is allocated to the M3 position.