Distribution of Fe in the fine fractions of some Czech bentonites

摘要: Distribution of Fe in the fine fractions four Czech bentonites was investigated by M6ssbauer spectroscopy. The spectra at room and liquid nitrogen temperatures revealed that most present samples is structurally bound smectite. Microcrystalline and/or Al-substituted goethite identified all fractions, comprising 8 to 50% total Fe. This mineral partly magnetically ordered Rokle sample even temperature. Two per cent hematite Kr~.sn~r Dvore~ek sample. Only octahedral Fe(IlI) found Stebno samples, while Kr~isn2~ Hrozn6tfn contained 9 38%, respectively, as Fe(II) 14% tetrahedral Fe(III) Kr~isn3) Dvore~ek. Several bentonite deposits are located Northwest part Republic. parent rocks ultrabasic basic effusives pyroclastics basanite, olivinic basalt tephrite types. Their autohydrothermal decomposition has led mainly formation Fe-bearing smectites, members beidellite-nontronite series (FranCe, 1983; Konta, 1986; Kraus & Kuf~vart, 1987; Cf6el et al., 1992a). Fine rarely mono- mineralic. Size fractionation increases clay content fraction, but usually does not completely remove admixtures. Some admixtures can be easily X-ray diffraction (XRD), those which minor amounts amorphous or poorly- crystalline may escape detection. Typical examples oxides/hydroxides, frequently bentonites, nontronites illites (e.g. Murad, Goodman 1988; Nadeau, Lear Murad Wagner, 1994). They often characterized small crystal size, high defect concentrations, foreign element substi- tutions, occasional deviations from stoichiometry, close intergrowths with other associated minerals. A ll these factors combine