The green marble of Prato, also called "serpentine", is a metamorphic rock belonging to the Apennine Serpentinite rocks. Typical of the Prato area, it was historically quarried around the medieval village of Figline, near Prato, in the foothills of the Apennines.
The charm of this stone, which has determined its essentially decorative function, lies primarily in its colour, which can display different shades of green, from light green to almost black, as well as yellow and green streaks, which have given it the name of "ranocchiaia (frog) stone".
The oldest quarries, the only ones from which the stone used to be excavated, are on Piano di Gello, on the eastern slopes of Monte Piccioli, near Figline.
The artistic success of the green stone of Prato coincided with the flowering of Romanesque architecture in Tuscany, and that of Florence in particular.
To the civilization of the Middles Ages, which sought its roots in the classical world, the serpentine stone of Prato was a stone that evoked with its colours and nobility of appearance the marbles of the architecture and precious marmoreal robes of ancient Rome.
This stone has been used in many sacred places in the historical centre of Prato, such as the facades of the Churches of San Domenico and San Francesco, in the Cathedral and in the Basilica di Santa Maria delle Carceri. Its use, however, was not limited to the area of Prato, but extended to Florence between the 11th and 12th centuries. The Baptistery, San Miniato, and the unfinished facade of the Badia Fiesolana are just a few of the Florentine structures featuring white marble and green stone of Prato facing.