Some variants of pietraforte can be found in the Overworld and some have to be crafted using various methods!
Where to find Pietraforte
Verdant Pietraforte generates in the forest and jungle biomes!
Ochre Pietraforte generates in the warm beach and desert biomes!
Marlot Pietraforte generates in the badlands and jungle biomes!
Ivory Pietraforte generates in mountains and hills!
These features use biome tags so custom biome support should be pretty easy!
You can turn Verdant Pietraforte to Ochre Pietraforte and vice versa using a Blast Furnace!
You can craft all the other colours using these two variants!