Abstract
The crystal structure of amesite-2H1 from the Postmasburg Mn ores of South Africa has been refined to R = 4.7% using Siemens P4 rotating-anode MoKα X-ray data and SHELXL-93 software. Partial ordering of tetrahedral Si,Al and especially of octahedral Mg,Al has reduced the ideal P63cm symmetry to triclinic P1 (refined as C1). Tetrahedral rotation of 15° moves the basal oxygens toward the octahedral cations in the same layer but away from the OH H-donors of the next layers. The ordering pattern of AlIV and AlVI is unique in that the locus of Al-rich sites consists of 2 intersecting sets of zigzag lines parallel to X2 and X3, plus 2 Al-rich octahedra in layer 2 instead of the usual 1 site.
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Zheng, H., Bailey, S.W. Refinement of an Amesite-2H1 Polytype from Postmasburg, South Africa. Clays Clay Miner. 45, 301–310 (1997). https://doi.org/10.1346/CCMN.1997.0450301
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DOI: https://doi.org/10.1346/CCMN.1997.0450301