Salt Crystal Intergrowth in Efflorescence on Historic Buildings

Abstract

Salt crystallisation is known to be one of the most powerful weathering factors threatening monuments, with the salts often occurring as efflorescence, normally formed from different species as individual salts growing in aggregates. In rare cases, different salt phases are observed that are closely intergrown on a crystalline scale. This paper reports on this rare type of salt efflorescence. Four types of salt crystal intergrowth in efflorescence have been distinguished up to now; the growth conditions for each are deduced.