Nordstrandite in Bauxite Derived from Phonolite, Lages, Santa Catarina, Brazil

Norberto Dani1, Milton Luiz Laquintinie Formoso1, Alain Decarreau2 and Alain Meunier2
1 Universidade Federal do Rio Grande do Sul, Instituto de Geociências, Avenida Bento Gonçalves 9500, CEP 91501-970, Caixa Postal 15001, Porto Alegre, Brazil
2 Hydrasa UMR 6532 CNRS, University of Poitiers, 40 Avenue du Recteur Pineau, 86022 Poitiers Cedex, France
E-mail of corresponding author: dani@if.ufrgs.br

Abstract: Nordstrandite from Lages represents the first occurrence of this mineral in an oxisoil that does not involve the influence of a calcareous substrate. This is also the first reported occurrence in Brazil. Nordstrandite occurs near the city of Lages only in the weathered bedrock facies, mostly where the circulation of meteoric water is restricted. There is also a close association between nordstrandite and the weathering of modified pseudoleucite structures. The interaction of meteoric water and feldspathic alkaline country rock with uncommon texture and mineralogy (rich in nepheline, sodalite, nosean, analcime and natrolite) promotes the development of solutions enriched in alkaline ions with basic pH, necessary to form nordstrandite. A detailed study by X-ray diffraction (XRD) and infrared (IR) spectroscopy in natural or chemically leached samples was performed to identify the Al(OH)3 polymorphs of gibbsite and nordstrandite.

Key Words: Bauxite • Boehmite • Gibbsite • Nordstrandite • Paraná Basin • Phonolite • Weathering

Clays and Clay Minerals; June 2001 v. 49; no. 3; p. 216-226; DOI: 10.1346/CCMN.2001.0490304
© 2001, The Clay Minerals Society
Clay Minerals Society (www.clays.org)