Comparison of Pedogenic and Sedimentary Greigite by X-ray Diffraction and Mössbauer Spectroscopy

Helge Stanjek and Enver Murad*
Lehrstuhl für Bodenkunde der Technischen Universität München D-85350 Freising-Weihenstephan, Germany
* Present address: Bayerisches Geologisches Landesamt, Concordiastrasse 28, D-96049 Bamberg, Germany.

Abstract: Greigites from a gley and a Tertiary sediment were investigated by X-ray diffraction and Mössbauer spectroscopy. The cell-edge length a of 9.8639 Å ± 0.0003 Å for the soil greigite was significantly smaller than that of the sedimentary greigite (9.8737 Å ± 0.0004 Å), but both cell-edge lengths were smaller than the value given on JCPDS card #16-713 (9.876 Å). Both greigites had 440 as strongest peak rather than 311 (as indicated on JCPDS card #16-713), but the other relative intensities did not deviate from the values given on this card within experimental error. Mean X-ray diffraction coherence lengths of 23 ± 2 nm for the soil greigite and of 60 ± 5 nm for the sedimentary greigite suggest superparamagnetic behavior. Mössbauer spectra nevertheless comprised two sextets with hyperfine fields of about 31.2 T (tetrahedral sites) and 30.7 T (octahedral sites), which resemble published values. It is postulated that aggregation may play an important role in determining the magnetic properties of the described samples.

Key Words: Greigite • Mössbauer • Sediment • Soil • XRD

Clays and Clay Minerals; August 1994 v. 42; no. 4; p. 451-454; DOI: 10.1346/CCMN.1994.0420411
© 1994, The Clay Minerals Society
Clay Minerals Society (www.clays.org)