• journal_title：Mineralogical Magazine
• Contributor：L. Secco ; F. Nestola ; A. Dal Negro ; L. Z. Reznitsky
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2008-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2008.072.3.785
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：72
• issue：3
• firstpage：785
• section：Articles

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.