Facetted garnets formed by etching. Examples from sandstones of Late Triassic age, South Germany



    1. Department of Geology, University of the Witwatersrand, Johannesburg, R.S.A.
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      Previous address: Institut für Geologie, Ruhr-Universität Bochum, Federal Republic of Germany.


Detrital garnets from the Upper Triassic (Keuper) of southern Germany have well developed facets where they occur in calcite-cemented sandstone. The grains belong to the pyralspite series and have a homogeneous chemical composition, without any zonation is revealed by microprobe analyses. It is concluded that the large facets are caused by etching during diagenesis and not by authigenic overgrowth. High calcium contents of the pore fluids may have been important in the formation of these garnet facets.