Taken inside the Loggia, which faces the Piazza della Signoria and is catty-corner to and just southwest of the Palazzo Vecchio.
What geological content could possibly be derived from this shot of Benvenuto Cellini's renowned Perseus with the Head of Medusa?
Hah. There's plenty of geology here. First off, there's the bronze statue itself—which the Florentine goldsmith-turned-sculptor-and-autobiographer had so much trouble casting. Most usually an alloy of copper and tin (it can also contain antimony and other metallic elements), bronze has been in continuous human use for at least seven millennia. Its primal ingredients come from cassiterite, the chief ore of tin, and such copper ores as chalcopyrite and chalcocite.
Not surprisingly, the bronze figure has been allowed to weather naturally to its attractive end state. That characteristic green tint signals the presence of copper carbonates, copper sulfates, or both. These compounds, which eventually succeed the deep-brown copper-oxide phase, form a protective patina and give the bronze an especially venerable appearance.
And then there's the pedestal that the mythological hero and the decapitated Gorgon corpse are set on. If you think it's marble, you're correct. It's the world-famous Carrara variety, quarried in the Apuan Alps about 100 km / 62 mi to the west-northwest of here.
This noble rock type began as marine sedimentary carbonate units deposited in the late Triassic and early Jurassic. Then it was metamorphosed into its present, finely crystalline form in the Oligocene and Miocene epochs. That change was effected when a slice of the crust called the Tuscan Nappe overrode another portion containing the Carrara's limestone protolith. This burial process generated the heat and pressure necessary to cook the carbonates into calcitic-to-dolomitic marble.
And there's still one other rock visible in this image. It's employed in the arches and vault ribs in the background. At first I wasn't sure which of the two widely used local sandstones, the Pietraforte and the Pietra Serena, it was. But according to one of my favorite sources on this city's architectural geology, Firenze University's Florence RockInArt website, this is the former selection. The Pietraforte comes from local turbidite deposits of late Cretaceous age.
Lastly, there's the facing material between the ribs. I assume it's stucco, the type of plaster applied on building exteriors. This too is a geologically derived building material.
If my guess is right and this is indeed stucco, it's reasonable to surmise that its primary component, lime, was produced by the burning of Alberese Limestone. The Alberese is the only carbonate rock type available in this part of Tuscany. It is turbiditic as well, but dates to the Eocene epoch.
Whew. See how much geologic history and petrology can be deduced from one old art-snobbler's photo?
You'll find the other photos and descriptions of this series in my Architectural Geology of Florence album.
