The role of salt fog on alteration of dimension stone

Limestones and silicate rocks used as dimension stone were submitted to cycles of salt fog, totalizing 140 days in a salt spray chamber. Rock samples comprised three types of limestone, three different marbles, six types of granites, two syenites, one gabbro and one basalt. Mineral changes and variation on surface luster, weight loss and salt crystallization on rock surfaces were some of the features observed along the exposure. While losses of weight and surface luster were the most striking features observed on carbonate rocks, mineral degradation was the main modification on silicate rocks, in which biotite showed to represent a key mineral in the alteration process due to its cleavage and possibly to its composition.