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.
Salts crystallisation is a cause of deterioration of stone monuments. Very small sizes of salt crystals, often a multiphase composition and usually low concentrations hamper their identification. Therefore, micro‐Raman spectroscopy, scanning electron microscopy and, in some cases, X‐ray diffraction have been used to identify the salts that crystallised within and on the weathered limestone and sandstone architectonic details of the Blessed Salomea sculpture and its arch in the cloister of the Poor Clares in Kraków, Poland. Possible sources of salts, i.e. regarding the plaster around the details, the mortar of joints of the arch and previous conservation procedures, have been discussed. The limestone sculpture reveals the presence of black crusts and the sandstone arch of white efflorescences, both stones crumble and exfoliate. Gypsum and barite were the only salts in the black crust and subflorescences of the limestone. The salts in the pore space of the sandstone include mainly aphthitalite, niter, nitratine and burkeite, while efflorescences consist of thenardite and syngenite. Such differences probably result from various precipitation conditions in narrow pore spaces and on the unconfined sandstone surface. The deterioration products have been mainly assigned to air pollution, stone itself in the case of the limestone, and migration of ions from structural elements of the arch in the case of the sandstone. The impact of the chemicals utilised for stone conservation also seems to be possible. Characterisation of the salts present in deteriorated stones can help in selecting the methods of stone desalination and conservation. Copyright © 2016 John Wiley & Sons, Ltd.
Previous research on rock weathering crusts has revealed their large variability depending on the type of host rocks and development of weathering processes. The composition of crusts developed on natural sandstone exposures is less documented in the literature in comparison to those developed on architectonic stones. In both cases, previous research has focused mainly on the progress of salt weathering. This study considers the surfaces of sandstone tors in the Polish Outer Carpathians. The exposed parts of the rocks in this area are often covered by crust, which is up to several centimetres thick, and differs from the internal part in colour and composition. The crusts were characterized using light and electron microscopy, X‐ray diffractometry, thermal analyses, Mössbauer spectroscopy, bulk chemical analyses and sequential chemical extractions. Porosity was estimated by digital image processing. The following two hardened zones were observed: (1) thin (up to 30 µm), black, external layer, rich in carbon and composed of opal‐type silica, covered in places by sulphate incrustations and numerous spherical particles of anthropogenic origin; (2) thicker (up to several millimetres), internal part composed of a set of laminae of variable colouration, enriched in iron (oxyhydr)oxides (goethite and hematite) in comparison to the rock interior. Development of the crust results from silicon and iron redistribution during the sandstone alteration. The chief source of silica is hydrolysis of aluminosilicates, whilst that of iron is decomposition of aluminosilicates, carbonates and sulphides. Hematite is probably a result of goethite transformation. However, air pollutants may play an important role in the formation of sulphates. Silica and iron compounds affect the properties of the rock, hardening the surface and lowering porosity by formation of secondary cement. Crystallization of sulphate salts, in turn, may contribute to mechanical disintegration of the rock. Copyright © 2013 John Wiley & Sons, Ltd.
and Tech nol ogy, Fac ulty of Ge ol ogy, Geo phys ics and En vi ron men tal Pro tec tion, al. A. Mickiewicza 30, 30-059 Kraków, Po landMarsza³ek, M., Dudek, K., Gawe³, A., Czerny, J., 2019. Min er al og i cal and geo chem i cal stud ies of sec ond ary min eral as semblages re lated to de te ri o ra tion of build ing ma te ri als. Geo log i cal Quar terly, 63 (4): 683-698, doi: 10.7306/gq.1494The study was aimed at min er al og i cal and geo chem i cal char ac ter is tics of sec ond ary phases re lated to de te ri o ra tion of historic build ing ma te ri als. The in ves ti ga tions, car ried out in the Holy Trin ity Ba sil ica in Kraków, Po land, fo cused on the south ern facade of the 17th-cen tury Myszkowskis Cha pel, built of the Mio cene Piñczów lime stone. Lower part of the facade is cov ered with a ce ment ren der, and the ex posed foun da tions are made of Ju ras sic lime stone and Cre ta ceous sand stone, both of lo cal or i gin from the Kraków re gion and neigh bour ing Carpathians, in the form of ir reg u lar blocks bound with a ce ment mor tar. The wall sur face ex hib its clear signs of dam age; from dark grey soil ing and scal ing to efflorescences. Sam pled ma te ri als, de te ri orated, al tered crusts and efflorescences were an a lysed with op ti cal and scan ning elec tron mi cros copy, X-ray dif frac tion, and Raman microspectroscopy meth ods. The sec ond ary min er als dis tin guished in clude abun dant gyp sum CaSO 4 ·2H 2 O, less com mon thenardite Na 2 SO 4 (and/or mirabilite Na 2 SO 4ÿ 10H 2 O), aphthitalite (K, Na) 3 Na(SO 4 ) 2 , darapskite Na 3 (SO 4 )(NO 3 )·H 2 O, ettringite Ca 6 Al 2 (SO 4 ) 3 (OH) 12 ·26H 2 O, monosulphite Ca 4 Al 2 O 6 SO 3 ·11H 2 O, as well as scarce ni tre KNO 3 , nitratine NaNO 3 and ha lite NaCl. Gyp sum usu ally forms sur face crusts and fills the pores in side some ma te ri als. The efflorescences, sam pled from the ex posed foun da tions, con sisted of thenardite and/or mirabilite, aphthitalite and darapskite, whereas ettringite and monosulphite were con nected with ce ment ren ders. Traces of ni tre, nitratine and ha lite were de tected at var i ous el e ments of the cha pel facade and foun da tions. The or i gin of the salts is re lated to com po si tion and physicochemical prop er ties of the build ing ma te ri als, as well as to anthropogenic fac tors.
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