Estudio previo de las «costras negras» desarrolladas sobre rocas graníticas en la catedral de Toledo

Abstract

Black crusts are typical chemical weathering features of diferent building materials. In this paper we present the preliminary results obtained through the study of the black crusts developed on some of the building materials of the Toledo Cathedral. These cruts (0.5-1.8 mm. thick) are main/y developed on fine-grained granites. They consist mainly of fine gympsum crystals however minor amounts of carbonates and fired carbonaceous patticles are also present As an hypothesis, weat- hering of the plagioclases and atmospheric S02 'are considered to be the sources of the gypsum crusts