Piedras de la arquitectura milanesa = Stone used in Milan architecture

The city of Milan lies in a large alluvial plain with high mountains as northern boundary. The plain deposits contain clays useful for brick-making and the mountains contain any kind of stones (igneous, sedimentary or metamorphic) useful for building; the transport of the stones was made possible by natural lakes and rivers and by long canals deliberately dug since medieval times. Milan was the capital of the Ducato set in the western part of the present-day territory of Regione Lombardia, the eastern part of this region was owned by Repubblica di Venezia. This territorial partition lasted until the end of 18th century and was witnessed by the different stones employed as building material. It is possible to detect five different zones utilised for the stone supply in Milan until 19th century: 1. Ossola valley, today part of Piemonte region but belonging to Ducato di Milano until 1748. Granites. Hercynian plutonism - Baveno pink and Montorfano white called "Graniti dei Laghi". Marbles. Ivrea-Verbano zone - Candoglia pink calcitic; Ornavasso dark veined calcitic. Monte Leone nappe of Lower Penninic Units - Crevola grey dolomitic. Gneiss. Antigorio nappe of Upper Penninic Units - Antigorio grey gneiss called "Serizzo Antigorio". 2. Lake Maggiore southern shore. Dolomite. Dolomia principale formation (Triassic) - Angera pink, yellow or white. 3. Val Ceresio, partly belonging to Canton Ticino (Switzerland) since 16th century. Detritic limestones. Calcari selciferi Lombardi formation (Jurassic) - Viggiù and Saltrio light brown or black calcarenites. 4. Brianza hills. Sandstones. Flysch di Bergamo formation (Cretaceous) - Viganò brown or grey called "Molera". Arenaria di Sarnico formation (Cretaceous) - Oggiono brown or grey. Granodiorite and gneiss. Boulders of glacial deposits called "Massi erratici". 5. Lake Como eastern shore. Limestone: Calcari di Perledo e Varenna formation (Triassic), Varenna black limestone. Marble. Dervio-Olgiasca zone of South Alpine basement: Musso grey or veined. Granodiorite and gneiss. Boulders from glacial deposits. 6. Adda river. Conglomerates and sandstones. Fluvial deposits (Quaternary) - Trezzo and Brembate multicoloured, called "Ceppo dell'Adda". It is possible a rough subdivision of the use of building stones during Milan history. The roman buildings were made of Ceppo dell'Adda conglomerate and of granodiorite called "Ghiandone" coming from glacial deposits. Coloured marbles coming from overseas regions as Greece, Turkey, Egypt etc. were widely used for flooring and wall coating. The early Christian period was characteized by reuse of roman building stones together with pebbles coming from nearby fluvial or glacial deposits; black limestones from Varenna (Lake Como) were used as floor tiles. The 11-13th centuries buildings show the use of bricks together with reused stones in some structural elements as columns or pilasters. The construction of the cathedral, called "Duomo", involved some centuries since 1386; the cathedral was made of Serizzo gneiss in the socle and Candoglia or Ornavasso marble for ashlar, decorative elements and sculptures. The churches of 15-16th centuries used the Angera dolomite because of its ease of working allowed to make decorative elements. The granites were used since the beginning of the 16th century mainly for columns and mouldings, the number of monolithic columns for porches and loggias increased during 17th century. The use of lime plaster was diffused since 18th century and the stone, mainly Viggiù and Saltrio calcarenites, was used for portals, balconies, windows or balustrades. The use of stone changed at the end of 19th century when the railways lines allowed the supply of stones coming from the whole Italian territory. At the beginning of the 20th cent