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Crystal-chemical study of Rc natural oxides along the eskolaite – karelianite – hematite (Cr2O3–V2O3–Fe2O3) join

Published online by Cambridge University Press:  05 July 2018

L. Secco*
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Via Giotto 1, I-35137, Padova, Italy
F. Nestola
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Via Giotto 1, I-35137, Padova, Italy Istituto di Geoscienze e Georisorse, CNR Sezione di Padova, Via Giotto 1, I-35137 Padova, Italy
A. Dal Negro
Affiliation:
Dipartimento di Geoscienze, Università di Padova, Via Giotto 1, I-35137, Padova, Italy
L. Z. Reznitsky
Affiliation:
The Siberian Division of Russian Academy of Sciences, Institute of the Earth’s Crust, Irkutsk, 664033 Russia
*

Abstract

Six natural crystals from the Sludyanka crystalline complex belonging to the eskolaite (Cr2O3)–karelianite (V2O3)–hematite (Fe2O3) solid solution were studied by means of X-ray diffraction and electron microprobe. The Fe3+-poor samples show a general increase in a and c cell parameters with increasing mean cationic radius (MCR), consistent with that shown by the synthetic crystals along the eskolaite–karelianite join. The Fe3+-richer sample deviates significantly from the behaviour shown by the Fe3+-poor ones, similar to synthetic and natural hematites; with increasing MCR, the a and c cell parameters increase linearly along the eskolaite-karelianite join. However, for the samples rich in Fe3+, from karelianite to hematite, a shows a slightly steeper slope whereas the c parameter decreases strongly. The octahedral distortion increases slightly as a function of MCR along the eskolaite-karelianite join, whereas it increases markedly for Fe3+-rich samples. The evolution of the octahedral edges and of the octahedral distortions as a function of MCR are responsible for the behaviour of the unit-cell parameters along the eskolaite-karelianite-hematite join.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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