SUDOITE IN SOME VISEAN (LOWER CARBONIFEROUS) K-BENTONITES FROM BELGIUM

Sudoite occurs as a cryptocrystalline clay in some Visean K-bentonites from Belgium. Usually associated with illite-smectite mixed-layers, this chlorite has been found locally as a monomineralic clay component of a K-bentonite bed. The mineral has a composition close to (Al3Mg2)(Si3Al)O10(OH)8. The cell parameters have been calculated from the diffractogram using the space group C2/m (a = 5-228, b = 9.056, c = 14.326 angstrom, beta = 97-degrees-00', d(060) = 1.509 angstrom). The polytype corresponds to a IIb structure. Some hypotheses are proposed for the origin of this chlorite. The coexistence of sudoite and pyrite could explain why the chlorite present in Visean K-bentonites is not a Fe-rich species typical of diagenetic conditions, but a Fe-poor one.