Elsevier

Geochimica et Cosmochimica Acta

Volume 41, Issue 9, September 1977, Pages 1355-1357, 1359-1361
Geochimica et Cosmochimica Acta

Ilmenite-type solid solutions between MgSiO3 and Al2O3 and some structural systematics among ilmenite compounds

https://doi.org/10.1016/0016-7037(77)90078-3Get rights and content

Abstract

Complete solid solutions with the ilmenite structure from pure MgSiO3 to 75% MgSiO3·25% Al2O3 have been synthesized in the pressure region between 240 and 300 kbar at 1000–1400°C in a diamond-anvil cell coupled with laser heating. The results suggest that complete solid solutions with the ilmenite structure might be formed between MgSiO3 and Al2O3 under high pressure-high temperature conditions. The lattice parameters for the ilmenite solid solutions between MgSiO3 and Al2O3 deviate from ideality in the same manner as those found by Berry and Combs along the FeVO3–Fe2O3 join. For the ordered A2+ B4+O3 ilmenite-type compounds, co is determined primarily by the size of the relatively large A2+ cation, whereas ao depends strongly on the radii of both A2+ and B4+ cations. Such systematics might account for the fact that co and ao for the ilmenite-type MgSiO3 are respectively smaller and larger than those for Al2O3. The lattice parameters ao and molar volumes for the A23+O3 corundum-type compounds and the disordered A2+B4+O3 ilmenites follow a different trend and are, therefore, readily distinguished from the ordered A2+B4+O3 ilmenites.

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Contribution No. 2856, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.

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