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Crystal field spectra and jahn teller effect of Mn3+ in clinopyroxene and clinoamphiboles from India |
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| Authors: | S Ghose M Kersten K Langer G Rossi L Ungaretti |
| Institution: | 1. Department of Geological Sciences, University of Washington, 98195, Seattle, Washington, USA 2. Institut für Mineralogie und Kristallographie, Technische Universit?t, D-1000, Berlin, West Germany 3. Centro di Studio per la Cristallografia Strutturale, C.N.R., Via Bassi 4, 27100, Pavia, Italy |
| Abstract: | Blanfordite (I), winchite (II), and juddite (III), all showing vivid colors and pleochroism, from highly oxidized parageneses of Indian gondites were studied by microprobe, Mössbauer, and microscope-spectrophotometric techniques and by X-ray structure refinements. The compositions of the Mn-bearing minerals were close to diopsideacmite (I) and magnesio-arfvedsonite to magnesio-riebeckite (II and III). Transition metal ions are located inM(1)-octahedra (I) or predominantlyM(2)-octahedra (II, III). Mössbauer spectra of57Fe(IS, ΔE Q) are typical of octahedral Fe3+ only. Polarized absorption spectra in the UV/VIS/NIR ranges explain color and pleochroism of the minerals. The position of the UV-“edge” is correlated with Fe3+-contents of the minerals, except for judditeE ∥Z, where the edge shows an unusual low energy position. This is most likely due to Mie-scattering of submicroscopic inclusions of braunite with nearly uniform dimensions. In the VIS range, the spectra are dominated by a complex band system between 15,000 and 20,000 cm?1. Energies and ?-values of component bands are compatible with those of Mn3+ d-d transitions in other Mn3+-bearing silicates. The polarization behavior of component bands can best be explained by aC 2(C2″) symmetry of the crystal field. The Jahn-Teller splitting (<9,000 cm?1) of the5 E g ground state of Mn3+ inO h crystal fields is appreciably smaller than in other Mn3+-silicates. Crystal field parameters 10Dq, (I) 13,650, (II) ca. 11,640, and (III) 11,925 cm?1, are near to that in piemontite. The crystal field stabilization energy of Mn3+, (I) 146, (II) ca. 140, (III) 142 \({{{\text{kJ}}} \mathord{\left/ {\vphantom {{{\text{kJ}}} {\text{g}}}} \right. \kern-0em} {\text{g}}}{\text{ - atom}}_{{\text{Mn}}^{{\text{3 + }}} } \) , is appreciably smaller than that found in other Mn3+-silicates (piemontites and manganian andalusites, viridines and kanonaite). |
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