The Loggia Cornaro is one of the most important monuments of Padua. The stone used is a marly limestone containing organogenic sediment and clay minerals in addition to calcium carbonate. The presence of thin interstratifications of montmorillonite causes the detachment of adjoining strata. The physical process of dissolution exerted by rainwater is further accelerated by the penetration along clay strata of acid solutions of sulfur compounds generated by atmospheric pollution. In areas protected from direct rainfall and surface run off the sulfate content is between 20 and 30%. On surfaces directly exposed to rainfall sulphate is present in lesser amounts of approximately 8-10%. Sulfate concentrations decrease sharply in the inner parts of the stone.