A comparison of properties of clay minerals in isalteritic and in degraded facies.

Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Varajão, César Augusto Chicarino; Boulangé, Bruno

A comparison of properties of clay minerals in isalteritic and in degraded facies.

Date

2013

Authors

Oliveira, Fábio Soares de

Varajão, Angélica Fortes Drummond Chicarino

Varajão, César Augusto Chicarino

Boulangé, Bruno

Abstract

The mineralogical, geochemical and micromorphological features of an isalteritic clay facies, which originated from weathering of an anorthosite, were compared to those of clay facies derived from the degradation of a bauxite developed from the same rock. The isalteritic clay was formed by the hydrolytic alteration of plagioclase, whereas the degraded clays were formed by decomposition of gibbsite and neoformation of kaolinite. This resilification process resulted from the reintroduction of silica via the oscillation of the phreatic level and/or the decomposition of organic matter on the surface. The degradation process was gradual and yielded two different facies: (a) degraded clays with almost total decomposition of gibbsite, and (b) degraded clays with gibbsite nodules. Morphologically, the isalteritic clays differ from the degraded clays because they contain larger hexagonal and pseudo-hexagonal crystals. The degraded clays have more irregular crystal shapes, ranging from laths to anhedral shapes.

Keywords

Isalteritic clay facies, Degraded facies, Anorthosite, Bauxite deg

Citation

OLIVEIRA, F. S. de et al. A comparison of properties of clay minerals in isalteritic and in degraded facies. Clay Minerals, v. 48, p. 697-711, 2013. Disponível em: <https://www.cambridge.org/core/journals/clay-minerals/article/comparison-of-properties-of-clay-minerals-in-isalteritic-and-in-degraded-facies/31FF5043B56CC834E4983BD1CA462977#>. Acesso em: 20 de jun. 2017.