『Abstract
　This work analyzes the stone superficial deterioration of some monuments in Rabat city. The rock is a calcarenite with porous texture, rich in calcium carbonates and fossils. The techniques used to study the surfaces altered by blackening or black crusts, are the SEM equipped with EDX microprobe, the X-ray diffraction, and the analysis of the soluble salts by ionic chromatography for anions and flame spectrometer for cations. They reveal significant contents of calcium sulphates, mainly gypsum, often associated with sodium chlorides. These salts known to have a destructive effect on the calcareous stones seem to be originated from the contamination by atmospheric pollutants, particularly sulfur dioxide, and by the marine sprays.

Keywords: Black crusts; Weathering; Salt deposits; Calcarenite; Almohade monuments; Rabat; Morocco』

Introduction
Monuments and material
Experimental methodology
Results
　Black crusts in rain-exposed areas at Bab Laalou and Bab Rouah Gates
　Black crusts in sheltered gateway of Bab El Hadd
　The quarry of Bou Knadel
The weathering process by salts efflorescence on calcarenitic stones
　Gypsum
　Halite
Conclusion
Acknowledgements
References