macigno
A quartzbearing sandstone so hard that during the it was favored for grindstones. In Florence it was also used in the construction of buildings. So abundant were its seams that all one had to do to build a house in Florence, it was said, was to dig a hole and then pile up the stones. Several quarries were actually found within the city gates, between the convent of Santa Felìcita and the Porta San Piero in Gattolino (now the Porta Romana); one of them was even owned by the convent’s nuns (King, 2000).