ISSN:
1432-2021
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
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 ɛ-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 $${{{\text{kJ}}} \mathord{\left/ {\vphantom {{{\text{kJ}}} {\text{g}}}} \right. \kern-\nulldelimiterspace} {\text{g}}}{\text{ - atom}}_{{\text{Mn}}^{{\text{3 + }}} } $$ , is appreciably smaller than that found in other Mn3+-silicates (piemontites and manganian andalusites, viridines and kanonaite).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00308346
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