Original paper

Crystal chemistry and cation distribution in some Mn-rich natural and synthetic spinels

Lucchesi, Sergio; Russo, Umberto; Della Giusta, Antοniο

European Journal of Mineralogy Volume 9 Number 1 (1996), p. 31 - 42

54 references

published: Dec 30, 1997
manuscript accepted: Sep 17, 1996
manuscript received: Mar 10, 1996

DOI: 10.1127/ejm/9/1/0031

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ArtNo. ESP147050901004, Price: 29.00 €

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Abstract

Abstract Four natural spinels pertaining to the jacobsite-franklinite join and a galaxite sample were studied by single-crystal X-ray diffraction and electron microprobe. The resulting cation distribution confirmed the tetrahedral site preference of Mn2+ with an increase in its inversion degree (max. about 0.16 vIMn2+/Mn2+tot.) at high jacobsite molar fractions. The amount of total Fe3+ was roughly constant in the three jacobsite samples. The entrance of Mn2+, mainly in the T site, displaces Fe3+ towards the M site where it substitutes for Mg. Magnesium, mainly ordered in the M site in jacobsite, shows a definite preference for the T site in galaxite. Only in one of the three jacobsite crystals was Fe2+ totally absent, as confirmed by Mossbauer spectroscopy, which also supported the Fe3+ intracrystalline distribution obtained by X-ray diffraction. On the basis of stoichiometry, the same sample also showed a definite amount of Mn3+. In the franklinite sample too, Mn2+ was strongly ordered in the tetrahedral site, in line with results observed in jacobsite samples with similar manganese content. Structural refinement of a synthetic MnCr2O4 spinel allowed improvement of the bond distance value (2.036 Å) of IVMn2+ in this class of compounds

Keywords

jacobsitefranklinitegalaxitesynthetic MnCr2O4crystal chemistry