The serizzi or sarizzi are part of the gneiss, metamorphic rocks of a light grey colour, with a very strong foliation, and which are typical of the Southern Alps. They can be found in Ossola and Valtellina.
Like the gneiss they are graniteidi orthogneiss and have hardness and resistance characteristics that make them more suitable for use with difficult requirements such as vehicular paving or as structural elements for building, and they are also typical coverings for stairways, sills, and passageways.
In addition to being the foundation material, a structural Serizzo stone archway, concealed by Candoglia, holds up the lantern of the Duomo. Even the old late-Romanesque church of San Simpliciano in Milan is based on large blocks of Serizzo stone. In modern houses in Milan nearly all the hurdles of window sills, pedestrian entrances and driveways, and even garages, are made of polished Serizzo stone.