『Abstract
Efflorescence, case hardening, and granular disintegration represent
common weathering features of Upper Cretaceous quartz sandstones
exposed in the Bohemian Switzerland National Park (NW Bohemia,
Czech Republic). Salt species (sulphates: gypsum (CaSO4・2H2O), potassium alum (KAl(SO4)2・12H2O), tschermigite (NH4Al(SO4)2・12H2O), alunite (K(Al3(SO4)2(OH)6),
and alunogen (Al2(SO4)3・17H2O), minor nitrates: nitrammite (NH4NO3)) determined by X-ray
diffraction exhibit vertical and geographic zoning. More soluble
salts (chlorides, nitrates, tschermigite) crystallize preferentially
on the cliffs exposed to the south, whereas the north face is
characterized by the presence of less soluble phases: gypsum and
K(Al3(SO4)2(OH)6. Vertical zoning of salt distribution on natural
outcrops differs from the salt distribution in masonry. Salt distribution
near the base of the cliff (profile to about 2-2.5 m above the
ground) is affected by capillary rise from the ground level (first
maximum of water-soluble salts at the level of 1-1.5 m above the
ground) and by percolation of precipitation through the overhanging
rock sequence (second maximum of 2-2.5 m above the ground). Percolation
of salt solution from higher parts is affected by the asperity
of the rock surface. The concentration of salts (determined by
ion exchange chromatography) correlates to the changes of physical
properties: bulk porosity, microporosity and water absorption.
The porosity, microporosity, moisture content and absorption generally
increase with the increasing volume of sulphates and nitrates.
Keywords: Sandstone weathering; Salts; Physical properties; Zoning;
Czech Republic』
Introduction
Study area and samples
Methods
Analysis of salt efflorescence
Determination of water-soluble salts
Rock petrography
Physical properties and pore system analysis
Results and discussion
Rock substrate
Phase and chemical composition of efflorescence
Origin of salts
Directional factors influencing salt distribution
Change of physical properties
Conclusions
Acknowledgments
References