Rubification of Terrae Rossae in Slovakia: A Mössbauer Effect Study

A. Bronger, J. Ensling, P. Gütlich and H. Spiering
Geographisches Institut, Universität Kiel D-2300 Kiel 1, Federal Republic of Germany
Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität D-6500 Mainz, Federal Republic of Germany

Abstract: Mineralogical and 57Fe Mössbauer spectroscopic analyses were made on seven terrae rossae and two terrae fuscae samples of Pliocene to Early Pleistocene age from Slovakia and limestone residues from their parent materials. In most of the samples, no mineral weathering or clay mineral formation could be detected by optical or X-ray powder diffraction investigation, compared with their parent limestone residues; only one terra rossa showed a strong weathering of primary feldspar and phyllosilicates and a high rate of clay formation, especially kaolinite. Mössbauer measurements between 5° and 300°K showed that hematite and goethite are the dominant color pigments in the rubified terrae rossae and their corresponding limestone residues. The mean particle size of hematite and goethite was estimated from Mössbauer effects and X-ray powder diffraction data to be 95 and 250 Å, respectively. Reduced values of the hyperfine fields at 5°K of the soil iron oxides, as compared with those of the pure oxides, indicate a partial substitution of Fe(III) by Al. The hematite content correlates with the Munsell color notation of 5 of the 7 terrae rossae samples and their corresponding limestone residues. All terrae rossae samples showed higher hematite contents than their corresponding limestone residues, indicating that the rubification of such materials is independent of the degree of weathering.

Key Words: Goethite • Hematite • Mössbauer spectroscopy • Terrae rossae • Weathering

Clays and Clay Minerals; August 1983 v. 31; no. 4; p. 269-276; DOI: 10.1346/CCMN.1983.0310404
© 1983, The Clay Minerals Society
Clay Minerals Society (www.clays.org)