Origin, characteristics and morphology of weathering crusts on Istria stone in Venice

To evaluate the effects of the environment on weathering of monuments of Is tria stone in Venice, systematic mineralogical, petrographical and elementa l analyses of depth profiles were performed on samples of surficial crusts (dendritic black, compact black, grey and white). Decay products of deposit ion and interactions between gases and stone, including wind blown dust, ma rine salts, anthropic aerosol, gypsum and nitrates, are incorporated into t he mineral matrix down to a depth of 10 mm. In areas sheltered from rain, w here black and grey crusts are observed, the high general humidity, carbona ceous particles and deposition of aerosols lead to the development of gypsu m and other salts. In compact and grey crusts decay products decrease; in g rey crusts carbonaceous particles are reduced, but in compact black crust p roducts of previous treatments are found. In white crusts, formed in areas experiencing effective wash-out, chemical and mechanical attack cause surfa ce recession. (C) 1999 Elsevier Science Ltd. All rights reserved.