Identifying Pseudorutile and Kleberite Using Raman Spectroscopy

Pseudorutile and kleberite are intermediate minerals formed during alteration of ilmenite to rutile. They are difficult to identify, as both have a range of chemical composition and occur as small crystals commonly mixed with other minerals. Reference samples of large crystals of pseudorutile and kleberite, with published X-ray diffraction and chemical analyses, were analysed to establish characteristic Raman spectra. Pseudorutile produced a goethite-like Raman spectrum but with a shift to increased wavenumber. It has characteristic Raman bands with peak positions at 234, 302, 402, 546, 617, 713 and 816 cm(-1) and OH stretching over the interval of 3390-3350 cm(-1). The 402 and 806 cm(-1) bands are the most intense. Kleberite produced a similar spectrum, but with a 10-30 cm(-1) greater Raman shift in the goethite-like bands. Its Raman bands have peak positions at 432, 573, 740, and 820 cm(-1) and OH stretching at 3390-3350 cm(-1). These results were applied to identify pseudorutile formed by diagenetic alteration of detrital ilmenite in Cretaceous sandstones of the Mesozoic Scotian Basin, eastern Canada. These samples showed pseudorutile Raman bands, but some samples are intermixed with residual ilmenite. Raman microspectroscopy thus allows rapid identification of small grains of pseudorutile and kleberite.