I don't think I've ever seen anything that said what kind of stone it's constructed from - even sites like great buildings just say stone http://www.greatbuildings.com/buildings/… . This site also just says stone, but it has a number of references you could look up if it's important. http://en.structurae.net/structures/data…

You might find this interesting: http://www.jstor.org/pss/1505633 It talks about the two most common building stones used in Florence and describes their composition.