Sféroidné pieskovcové konkrécie v malcovskom súvrství v Hruštíne na Orave

Primary and secondary occurrences of larger sandstone spheroidal concretions (balls), which are not yet mentioned in professional or popular literature, were found in Hruštín village (Slovakia) and its surroundings during of detailed geological mapping and research of the Oravská Magura region. 58 spheres, or parts of them, with diameters ranging from 30 to 220 cm were recorded. The smaller ones are usually regularly round. The flattened spheroidal to ovoid shape prevailed in the larger ones. The aim was to locate as many occurrences as possible, specify their exact GPS location, photo-documentation, and a brief description of their shape and location. The primary occurrences of the spheres are related to a specific lithotype of predominantly medium-grained quartz-greywacky sandstones in the early Oligocene part of the Malcov Formation. Originally, spheres are sandstone concretions that were formed by preferential cementation after sedimentation of deep-sea sandy gravity currents during the initial phase of sediment diagenesis, but before its complete lithification. The conditions of concretion formation, comparison with similar occurrences of spheres in Slovakia, neighbouring countries, as well with more than 60 world locations and the potential for geotourism and the need for discovery sites protect are briefly discussed in the conclusion.