Coexistence of halloysite and kaolinite: a study on the genesis of kaolin clays of Campo Alegre Basin, Santa Catarina State, Brazil

Abstract

Kaolin at Campo Alegre Basin, Santa Catarina State, Brazil was formed from alteration of volcanic acid rocks. Halloysite clays dominate the clay fraction of the matrix of the kaolin body, whereas a poorly crystalline kaolinite is abundant in veins. Some primary blocky structures have high amounts of illite, in one mine, but in general, only low contents of illite-smectite, illite, chlorite-vermiculite, vermiculite and quartz were identified in the clay fraction of the samples. Toward the top of the mines, hematite and lepidocrocite appear in horizontal red and ochre colored levels and the amount of kaolinite increases compared to halloysite. The vertical zoning of alteration levels, the changes in mineralogy, the positive correlation between depth and Cation Exchange Capacity of the clays, the preservation of different types of rock textures in the kaolin bodies, the dominant tube morphology of the halloysite clays indicate a supergene genesis for the deposits. Criteria to distinguish between supergene and hypogene kaolin are discussed. Transmission Electron Microscopy of the cross sections of halloysite tubes showed polygonal forms that are ascribed to be transitional between kaolinite and halloysite. It is proposed that some of the kaolinite of these deposits be inherited from the dehydration of halloysite tubes.<br>O caolim da Bacia de Campo Alegre, Estado de Santa Catarina, Brasil, formou-se da alteração de rochas vulcânicas ácidas. A haloisita predomina na fração argila da matriz do corpo de caolim, enquanto a caolinita, de baixa cristalinidade, é abundante nos veios. Algumas estruturas em blocos, primários, têm altos teores de ilita em uma mina, mas no geral, somente foram identificadas, na fração argila das amostras, baixas quantidades de ilita-esmectita, ilita, clorita-vermiculita, vermiculita e quartzo. Em direção ao topo das minas aparecem hematita e lepidocrocita em níveis vermelhos e ocres e as quantidades de caolinita aumentam, se comparadas às de haloisita. O zoneamento vertical dos níveis de alteração, as mudanças mineralógicas, a correlação positiva entre profundidade e Capacidade de Troca de Cátions das argilas, a preservação de diferentes tipos de textura de rochas nos corpos de caolim e o predomínio da morfologia tubular da haloisita indicam uma origem supergênica para os depósitos. São discutidos critérios para distinguir entre caolins supergênicos e hipogênicos. A Microscopia Eletrônica de Transmissão das secções transversais dos tubos de haloisita mostrou formas poligonais que são atribuídas a transições entre caolinita e haloisita. Propõe-se que algumas das caolinitas destes depósitos sejam herdadas da desidratação de tubos de haloisita

Applications and interfaces of halloysite nanocomposites

“…(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Reprinted with permission from Ref Oliveira et al (2007),Yuan et al (2008),. andVergaro et al (2010).…”

Spiral Structure of 7 Å Halloysite: Mathematical Models

“…Studies have provided explanations for the mechanism by which planar kaolinite rolls to tubular halloysite (Singh, 1996). Powder XRD patterns of the two minerals overlap and can be transformed from one to the other (La Iglesia and Galán, 1975;Bobos et al, 2001;Oliveira et al, 2007).…”

Simulation of the nucleation and growth of simple clay minerals in weathering processes: The NANOKIN code

“…Kleber et al (2007) studied the competition between halloysite and kaolinite in tropical rain forest soils. Oliveira et al (2007) showed the coexistence of halloysite and kaolinite in kaolin clays from alteration of volcanic rocks and proposed that some kaolinite may be inherited from halloysite precursors. From a theoretical point of view, Trolard et al (1990) considered the possible kaolinite-halloysite competition on a thermodynamical basis and Steefel and Van Cappellen (1990) simulated their formation as a result of granite dissolution, in a reaction-flow system, not directly comparable to the conditions of our simulations which correspond to a batch-type experiment.…”