A new Al-rich hydroxylian pseudorutile from Kalimantan, Indonesia

A new type of Al-rich hydroxylian pseudortuile (HPR), containing 64.6 wt% Ti[O.sub.2], 12.1 wt% [Al.sub.2][O.sub.3], 10.9 wt% [Fe.sub.2][O.sub.3], and 12.4 wt% [H.sub.2]O, has been identified in detrital heavy mineral concentrates from Central Kalimantan, Indonesia. The unusual translucent orange-colored grains have been characterized using electron microprobe analyses, thermal analyses, [sup.27]Al MAS NMR, and synchrotron XRD studies including the use of differential pair distribution function analysis, to determine how the Al is incorporated. The results support a model in which diaspore-form AIOOH is incorporated into nanopores in the solid hydrogel-like mineral. The HPR matrix structure comprises disordered unit-cell scale intergrowths of diaspore-type and rutile-type structure elements, which have a close dimensional match to the diaspore structure, thus providing a suitable template for epitactic nucleation and growth of the diaspore. The average composition of the grains is [Fe[Ti.sub.6][O.sub.10.8][(OH).sub.5.4]] x 1.8A1OOH x [H.sub.2]O, where the formula within the square brackets represents the HPR matrix, and the A1OOH and [H.sub.2]O occupy the intragrain pore volume. Keywords: Hydroxylian pseudorutile, Al-rich pseudorutile, synchrotron XRD study, diaspore-rutile intergrowth structure DOI: 10.2138/am.2010.3330