Las bentonitas de Benavila (Portugal)Caracterización mineralógica y propiedades

  1. Isabel Dias, M.
  2. Prates Filho, J. S.
  3. Suárez Barrios, María Mercedes
Journal:
Geogaceta

ISSN: 0213-683X

Year of publication: 2003

Issue: 35

Pages: 99-102

Type: Article

More publications in: Geogaceta

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Abstract

The igneous massif of Benavila (Portugal) is constituted by rocks of granitoid nature, especially granodiorites associated to quartzdiorites, partially covered with palaeogenic sediments. A chemical, mineralogical and textural characterisation of clay materials deriving from weathering of those rocks has been done. Clays resulting of the weathered granodiorites of Benavila, are very rich in smectites. The X-ray diffraction (XRD) results of the bulk sample enhance the clayey characteristics of those materials, mainly associated to calcite, and traces of quartz and feldspars. A monomineralic clay sample has been chosen for a more detailed study. The clay fraction XRD results enhance the presence of only smectite, that is well crystallized and dioctahedral. A structural formula for this smectite of Benavila is proposed. The chemical analysis points to a Tatatila smectite type, relatively enriched in iron. The exchange cation capacity has been calculated in the bulk sample and in the < 2 f-lm fraction. The Specific Surface area has been evaluated in the 77°K nitrogen adsorption-desorption isotherms, applying the BET method. A porosity study has also been made through the t-curves. The results obtained with all those analyses are lower than the usually presented in literature.