Chemical composition and Decay Patterns of Stones used in Pasargadae World Heritage Site

The stones used in Pasargadae world heritage site are different in texture and color as well as chemical characters. Despite equal environment condition, they have been damaged in different forms. The aim of this study is Identification of stones compositions and decays through XRD and XRF analysis. Also, some surface investigations have been done by Digital Macroscopic and Scanning Electron Microscope (SEM) in order to show surface deterioration. The analyses declare that all stone types are three different kind of limestone. Two types of the limestone that are in beige and dark gray color have a compact texture, but the third one that is in green gray color has fairly porous structure. The main phase was reported in X-ray diffraction analysis is Calcite (CaCO3), in addition, minor amount of quartz phase (SiO2) have also been reported. In some beige stone analysis, dolomite phase was observed and the quality of dolomite (Ca,Mg(CO3)2) and calcite were approximately equal in ratio. Despite the possibility of salt presence as a decay factor, the X-ray diffraction analysis did not report any salt. There are two possibilities; first, salt is not a factor in decay phonemes of Pasargadae stones, second, the amount of salt is low enough not to identifying through this analysis. According to microscopic and microstructure images, the main decay reason of dark and green gray types is their intrinsic problems. The main decay factor on beige stone is lichens mechanism. However, if the formation of Patina is caused by lichen, the lichen was useful in some case, because the patina as a coating covered the surface of stone and increased surface defense. Hence, the results of experiments and observations determine that the main environmental decay factors in Pasargadae World Heritage Site are microorganism and water duo to calcite dissolution and clay swelling.