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Weathering of Ilmenite in a Lateritic Pallid Zone

Published online by Cambridge University Press:  02 April 2024

R. R. Anand  and
R. J. Gilkes
R. R. Anand
Affiliation:
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia 6009, Australia
R. J. Gilkes
Affiliation:
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia 6009, Australia
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Abstract

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In a lateritic pallid zone ilmenite crystals alter via pseudorutile to porous leucoxene grains composed of randomly oriented aggregates of ~0.06 μm anatase crystals. This style of alteration differs from that in beach sands where parallel oriented rutile crystals develop from pseudorutile. Increased Si and Al in the altered grains is due to the crystallization from soil solution of halloysite, kaolinite and gibbsite within pores rather than to the incorporation of these elements into anatase crystals. Manganese was a significant constituent (3.2% Mn2O3) of the original ilmenite but was not retained by the leucoxene grains. The minor constituents Ni, Zn, Cu, Mg, Co and Ca were also lost, but Cr and V were retained.

Резюме

Резюме

В латеритовой бледной зоне кристаллы ильменита видоизменяются через псевдорутил в зерна пористого лейкоксена, состоящие из агрегатов беспорядочно ориентированных ~0,06 μm крис¬таллов анатаза. Этот тип видоизменения отличается от типа в пляжных песках, в которых парал¬лельно ориентированные кристаллы рутилов развиваются из псевдорутилов. Увеличенное содержание 81 и А1 в видоизмененных зернах обусловлено кристаллизацией галлуазита, каолинита и гиббсита из почвенного раствора внутри пор скорее, чем в результате включения этих элементов в кристаллы анатаза. Марганец являлся значительным составным элементом (3,2% Мn2О3) первоначального иль¬менита, но не удерживался зернами лейкоксена. Второстепенные составные элементы Ni, Zn, Сu, Мg, Со, и Са были также потеряны, но Cr и V удерживались. [E.G.]

Resümee

Resümee

In einer lateritischen palliden Zone wandeln sich Ilmenitkristalle über Pseudorutil in poröse Leucoxenkörner um, die aus Aggregaten von unregelmäßig angeordneten etwa 0,6 μm großen Anatas-kristallen bestehen. Diese Umwandlungsart unterscheidet sich von der in Küstensanden, wo sich parallel orientierte Rutilkristalle aus dem Pseudorutil bilden. Eine Zunahme des Si- und Al-Gehaltes in den umgewandelten Körnern rührt eher von der Kristallisation von Halloysit, Kaolinit und Gibbsit in den Poren aus der Porenlösung her als vom Einbau dieser Elemente in die Anataskristalle. Mangan war in beachtlichen Mengen (3,2% Mn2O3) im ursprünglichen Ilmenit enthalten, wurde aber durch die Leucoxenkörner nicht zurückgehalten. Die Spurenelemente Ni, Zn, Cu, Mg, Co, und Ca gingen ebenfalls verloren, während Cr und V zurückgehalten wurden. [U.W.]

Résumé

Résumé

Dans une zone ilménite latérite pâle, des cristaux sont altérés via la pseudorutile en grains leucoxènes poreux composés d'aggrégats de cristaux d'anatase de ~0,6 μm orientés au hasard. Ce style d'altération diffère de celui du sable de plage où des cristaux de rutile orientés parallèlement se développent à partir de la pseudorutile. L’élévation du contenu en Si et Al dans les grains altérés est due à la cristallisation à partir de solutions du sol d'halloysite, de kaolinite, et de gibbsite endéans les pores plutôt qu’à l'incorporation de ces éléments dans les cristaux anatase. La manganèse était un constituent significatif (3,2% Mn2O3) de l'ilménite originale, mais n'a pas été retenue par les grains leucoxènes. Les constituents mineurs Ni, Zn, Cu, Mg, Co, et Ca ont aussi été perdus, mais Cr et V ont été retenus. [D.J.]

Keywords

AnataseHalloysiteIlmeniteKaoliniteLateriteLeucoxenePseudorutileRutileWeathering
Type
Research Article
Information
Clays and Clay Minerals , Volume 32 , Issue 5 , October 1984 , pp. 363 - 374
Copyright
Copyright © 1984, The Clay Minerals Society

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