Crystal chemistry of some Mg, Cr, V normal spinels from Sludyanka (Lake Baikal, Russia): the influence of V3+ on structural stability

A suite of vanadian magnesiochromites from the Sludyanka metamorphic complex (South Lake Baikal, Russia) were investigated by means of X-ray single-crystal structural refinements and microprobe analyses. Various morphological types of Cr-V-bearing Mg spinels are located in calc-silicate metamorphic...

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Bibliographic Details
Published in:Physics and Chemistry of Minerals
Main Authors: B. Lavina, L. Z. Reznitskii, BOSI, Ferdinando
Other Authors: B., Lavina, L. Z., Reznitskii, Bosi, Ferdinando
Format: Article in Journal/Newspaper
Language:English
Published: SPRINGER-VERLAG 2003
Subjects:
v-magnesiochromite
spinel
crystal chemistry
sludyanka
magnesiocoulsonite
karelia*
Online Access:http://hdl.handle.net/11573/140045
https://doi.org/10.1007/s00269-003-0354-y
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Summary:A suite of vanadian magnesiochromites from the Sludyanka metamorphic complex (South Lake Baikal, Russia) were investigated by means of X-ray single-crystal structural refinements and microprobe analyses. Various morphological types of Cr-V-bearing Mg spinels are located in calc-silicate metamorphic rocks, in an assemblage that also contains other Cr-V minerals such as escolaite-karelianite, uvarovite-goldmanite, Cr-V-bearing clinopyroxene, tourmaline, amphibole, mica, etc. Along the suite there is widespread V-Cr substitution (0.14 less than or equal to V3+ less than or equal to 0.95 afu, 1.02 less than or equal to Cr3+ less than or equal to 1.80 afu), and minor, variable Al contents. The Mg content of slightly lesser than 1 afu, is almost constant. Cell parameters and octahedral bond distances increase with V3+. Unexpectedly, the Mg-O tetrahedral bond distance also increases slowly with V3+. This weak dragging effect contributes towards maintaining distortion of the oxygen array with respect to the ideal CCP, thus providing a shielding effect, which reduces V3+-V3+ repulsion. This leads to the energetic stabilization of the structure, in spite of the increase of bond strain with increasing V3+ contents.

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