Nickel-Containing Montmorillonites and Chlorites from Brazil, with Remarks on Schuchardtite

G. W. Brindley and Jefferson V. De Souza1
Materials Research Laboratory and Dept. of Geosciences, The Pennsylvania State University, University Park, PA 16802
1On leave of absence from the Technological Research Institute of the University of the State of São Paulo, São Paulo, Brazil (Instituto de Pesquisas Tecnologicas da Universidade do Estado de São Paulo).

Summary: Clay-like, hydrous nickel silicates from Niquelandia, Goias, Brazil, and from Jacupiranga, São Paulo, Brazil, are examined by X-ray diffraction, chemical analysis, and thermogravimetric methods. The nickel silicates from Niquelandia are ferric iron montmorillonites, with nickel in the octahedral positions and, to a lesser extent, in interlayer positions. The chemical compositions of samples dried at 110 °C average (Mg0·15Ni0·06Ca0·015Na0·005)(Fe0·92IIIFe0·025IIAl0·55Mg0·37Ni0·22)(Si3·88Al0·12)O10(OH)2(H2O)0·93. The layer charge originates largely in the octahedral sheet. The cation-exchange capacities average 107 me/100 g clay (110 °C). These minerals differ from nontronites, in which the layer charge originates mainly in the tetrahedral sheets.

The nickel silicates from Jacupiranga resemble chlorites, with a non-expanding basal spacing of 14·2–14·3 Å. The better crystalline forms give X-ray data in good agreement with a Ia polytype structure, which is consistent with their formation by low-temperature processes. Chemical formulae derived on the basis of O10(OH)8 give an average of 5·47 cations in octahedral positions. Thermogravimetric measurements show up to 4% H2O lost between 110 and 500 °C. These results suggest a partial vermiculitization of the interlayer sheets. A new method of calculating a structural formula is developed that gives an interlayer composition of the form R1·75(OH)3·75(H2O)1·14, with (OH + H2O)/R - 2·80, which approaches the ratio for a dioctahedral sheet structure.

A comparison of these defect chlorites with available data on schuchardtites shows many similarities; however, schuchardtite is not yet sufficiently well defined for the Jacupiranga chlorites to be given this name.

Clay Minerals; June 1975 v. 40; no. 310; p. 141-152; DOI: 10.1180/minmag.1975.040.310.04
© 1975, The Mineralogical Society
Mineralogical Society (