Crystal Caves in the ‘Wieliczka’ Salt Mine – unique cave site

Crystal Caves are two partly natural chambers situated in the eastern part of the „Wieliczka” Salt Mine, about 80 m underground. The chambers were discovered in the end of the 19th century. They are elements of the mine that has existed since the Middle Ages and is currently exhausted, inscribed on the UNESCO World Cultural and Natural Heritage List in 1978 and declared as the National Historical Monument. The Crystal Caves are located within the boulder part of the salt deposit in the Miocene sequence of the Carpathian Foredeep. Their walls are coated with crusts, aggregates and individual coarse halite crystals ranging from several up to 34 cm in size. Several genetic hypotheses of the Crystal Caves have been considered. The discovery of residual sand-clay formations below the Crystal Caves confirms the thesis on karst origin of these chambers but preceded by rock massif disruption and opening of cracks due to tectonic stresses. Subsequent development of coarse crystalline halite formations occurred during the cold (glacial) periods of the Quaternary, owing to slow halite precipitation. Since the discovering, the Crystal Caves and their crystal formations were considered to be the unique natural geoheritage and, therefore, they were more or less protected, but on the other hand, the crystals were periodically extracted for scientific, educational and commercial purposes. The regulation of their legal status as a nature reserve took place in 2000. The scientific study performed in 1992 –1997 has proved that apart from the direct human activity (extraction of crystals), the most dangerous threats of crystals include the destruction (leaching) of halite crystals caused by air humidity. Since that time, the microclimatic conditions adequate for crystalline decor protection has been observed in the Crystal Caves. The realization of a conservation program for the “Crystal Caves” Nature Reserve for the period 2011– 2031 by the “Wieliczka” Salt Mine management has been supervised by the Commission for Protection of the Crystal Caves.