Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

The facetted surface of a sandstone pebble from Quaternary deposits at Karlštejn (central Bohemia; Czech Republic)


Radek Mikuláš

Geoscience Research Reports 45, 2012 (GRR for 2011), pages 87–90
Map sheets: Beroun (12-41)

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An ovoid pebble of quartz sandstone, 11 cm in size, found in Holocene deposits at Karlštejn, bears perfectly developed polygonal facets. They represent a pattern of sandstone/quartzite microrelief that develops most often in arid to semi-arid conditions, or under specific chemism responsible for a higher mobility of Si02. The quartz sandstone probably belongs to the local silcrete, Cretaceous to Tertiary in age. Based on observed and published analogues, we presume that the facets originated on the subaerially exposed surface of a Pleistocene terrace of the Berounka River. The pebble was probably relocated and modified in Neolithic times, when used as a smear-stone.