That's a bunch of schist

OK it's a rock

Or Galestro - Schist (from Wikipedia) based soil found in the Tuscany region of Italy. It is a laminated, crystalline rock based soil that retains heat well and is rich in magnesium and potassium but poor in organic nutrients and nitrogens.

Found in Tuscany.

Retains heat and is rich in magnesium and potassium.

Pretty good stuff considering the wines that come from that area.