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Hydroxylian pseudorutile derived from picroilmenite in the Murray Basin, southeastern Australia

CSIRO Minerals, Box 312 Clayton South, Victoria, Australia 3169

^* E-mail: ian.grey{at}csiro.au

Ilmenite concentrates obtained from heavy mineral deposits in the Murray Basin, southeastern Australia contain appreciable quantities (up to 10 wt.%) of an unusual hydrated Fe titanate mineral in the form of orange to red coloured translucent grains. The grains are weakly magnetic and have a low apparent density (<3.3 g cm^–3) due to microprosity, which enables them to be easily concentrated in a pure state. Samples from different deposits have similar analyses of 67–69% TiO₂, 8–9% Fe₂O₃, 2–3% FeO, 11–12% H₂O and 8–9% of intra-pore impurities, mainly SiO₂ and Al₂O₃. The powder pattern for the mineral closely matches that for pseudorutile; having a hexagonal subcell with a = 2.844 (1) Å, c = 4.575 (1) Å. The idealized composition range of the Fe titanate, calculated from analyses and structure refinements, is [FeTi₆O₁₂(OH)₃].3H₂O to [FeTi₆O₁₁(OH)₅].2H₂O. The molecular water is non-structural, probably adsorbed on the surfaces of nano-scale domains of the mineral. Electron microprobe and scanning electron microscopy studies provide evidence for formation of the mineral by replacement reactions acting on MgO-rich ferrian ilmenite grains. The mineral represents a distinct intermediate in the chemical weathering of ilmenite, having a pseudorutile-like structure but a leucoxene-like composition. It is unusual in not having undergone any recrystallization to phases such as rutile and anatase.

KEYWORDS: pseudorutile, ilmenite, Australia, Murray Basin, iron titanate

This article has been cited by other articles:

				I. Grey, C. MacRae, E. Silvester, and J. Susini Behaviour of impurity elements during the weathering of ilmenite Mineralogical Magazine, August 1, 2005; 69(4): 437 - 446. [Abstract] [Full Text] [PDF]