Alteration Of Ilmenite Research Articles

Ilmenite alteration under reducing conditions in unconsolidated sediments

Discussion of a paper by J.W. Gruner (Geoscience Abstracts 1-3102). Nonmarine Cretaceous sediments in the Maryland Coastal Plain contain authigenic rutile, pyrite, and siderite. The presence of siderite and pyrite indicate a redox potential of between -0.1 and -0.3. The pH was about 3 - 4 because many of the clays are now acid. The alteration of ilmenite to rutile and pyrite accounted for only a small part of the total pyrite. Certain bauxites formed in reducing conditions also contain authigenic minerals.

The alteration of ilmenite in beach sands

Study of the heavy mineral assemblages of beach sands from Mozambique, Ceylon, Florida, and Brazil indicates that they consist largely of ilmenite in various stages of alteration. Three successive stages of alteration are recognized, and their optical and X-ray characteristics are described. The final product of alteration is commonly finely crystalline rutile, but leucoxene composed of finely divided brookite has also been identified.Alteration is accompanied by progressive decrease in magnetic susceptibility. The materials studied can be separated magnetically into fractions in which ilmenite grains showing various stages of alteration are concentrated differentially. The fractions therefore differ markedly in chemical composition.