Journal of Petrology Advance Access originally published online on June 13, 2005
Journal of Petrology 2005 46(9):1881-1892; doi:10.1093/petrology/egi038
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An Experimental Study of Fe–Al Solubility in the System Corundum–Hematite up to 40 kbar and 1300°C
1 GEOFORSCHUNGSZENTRUM POTSDAM, DEPARTMENT 4, TELEGRAFENBERG, D-14473 POTSDAM, GERMANY
2 FREIE UNIVERSITÄT BERLIN, DEPARTMENT OF EARTH SCIENCES, MALTESERSTRASSE 74–100, D-12249 BERLIN, GERMANY
RECEIVED AUGUST 9, 2004; ACCEPTED MARCH 16, 2005
The mutual solubility in the system corundum–hematite [
-(Al, Fe3+)2O3] was investigated experimentally using both synthetic and natural materials. Mixtures of 
-Al2O3 and -Fe2O3 (weight ratios of 8:2 and 10:1) were used as starting materials for synthesis experiments in air at 800–1300°C with run times of 7–34 days. Experiments at 8–40 kbar and 490–1100°C were performed in a piston-cylinder apparatus (run times of 0·8–7·4 days) using a natural diasporite consisting of 60–70 vol. % diaspore and 20–30 vol. % Ti-hematite. During the diasporite–corundite transformation, the FeTiO3 component (12–18 mol %) of Ti-hematite only slightly increased, implying that oxygen fugacity was maintained at high values. Run products were studied by electron microprobe and X-ray diffraction (Rietveld) techniques. An essentially linear volume of mixing exists in the solid solution with a slight positive deviation at the hematite side. Up to 1000°C, corundum contains <4 mol % Fe2O3 and hematite <10 mol % Al2O3; at 1200°C these amounts increase to 9·3 and 17·0 mol %, respectively. At 1300°C hematite was no longer stable and 
coexists with the orthorhombic phase 
. The present results agree with corundum (solvus) compositions obtained in previous studies but indicate a larger solubility of Al in hematite. The miscibility gap in the solution can be modelled with an asymmetric Margules equation with interaction parameters (2
uncertainties): 
; 
; 
; 
. Application of the corundum–hematite solution as a solvus geothermometer is limited because of the scarcity of suitable rock compositions.
KEY WORDS: corundum; hematite; corundum–hematite miscibility gap; experimental study; Margules model; metabauxite
* Corresponding author. Telephone: 0 (331) 288-1415. Fax: 0 (331) 288-1402. E-mail: feenstra{at}gfz-potsdam.de
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