Efflorescences on weathered sandstone tors in the Stone Town Nature Reserve in Ciezkowice (the Outer Carpathians, Poland)-their geochemical and geomorphological controls.

The study area within the Stone Town Nature Reserve in Ciezkowice encloses a variety of occurrences of sandstone tors exposed within the Skala Hill (Rock Hill) from its top down into the Biala River Valley. The efflorescences of salt minerals on the walls of the sandstone tors represent end products of weathering. Several types of the efflorescences have been distinguished in relation to their distribution, the composition of the parent sandstones and local conditions of the natural environment. Laboratory methods have allowed identifying several sulphate minerals of various hydration (mainly pickeringite, hexahydrite, pentahydrite, alunogen, K-alum, gypsum, syngenite). They occur as two morphological varieties: as accumulations of a millimetre large flakes or as granules. The development, diversification and distribution of the efflorescences depend first of all on the rock moisture controlled by its capillary rise. The dampness of the lower tor parts is relatively the major factor; thus, such places are the sites favouring efflorescing phenomena. The presence of sulphur-bearing ions that are contained in salt minerals may be attributed to oxidation of pyrite occurring in the sandstone formations in the vicinity of Ciezkowice but may also be associated with local waters, more probably with mineral ones than with groundwater recharged by atmospheric precipitations. Air pollution, particularly with sulphur compounds, should also be considered in weathering of sandstone tors and the formation of the efflorescences.

Composition of weathering crusts on sandstones from natural outcrops and architectonic elements in an urban environment.

This work presents mineralogical and chemical characteristics of weathering crusts developed on sandstones exposed to various air pollution conditions. The samples have been collected from sandstone tors in the Carpathian Foothill and from buildings in Kraków. It has been stated that these crusts differ in both fabric and composition. The sandstone black crust from tors is rich in organic matter and composed of amorphous silica. Sulphate incrustations accompanied by dust particles have been only sometimes observed. Beneath the black crust, a zone coloured by iron (oxyhydr)oxides occurs. The enrichment of the surface crust in silica and iron compounds protects the rock interior from atmospheric impact. The sandstones from architectonic details are also covered by a thin carbon-rich black crust, but they are visibly loosened. Numerous salts, mainly gypsum and halite, crystallise here, thus enhancing deterioration of the rock. Moreover, spherical particles originated from industrial emissions are much more common. Gypsum in natural outcrops, forms isolated and well-developed crystals, whilst these found on the architectonic details are finer and densely cover the surface. Such diversity reflects various concentrations of acid air pollutants in solutions.