1) Volcanic rock 
Sillar is a whitish volcanic stone from which many colonial buildings in the city of Arequipa, Peru, are made. A fine example are the Arcs of the `Mirador of Yanahuara` in Arequipa, from which the entire city can be appreciated. The stone, a vapour-phase crystallized tuff produced by the now-extinct Chachani volcano during the Pleistocene era, w.....