Etruria Marl is a type of marl or clay that can be found in the overworld.
Etruria Marl is found in the overworld in large veins. It's generally found underground and sometimes on the surface at low altitudes. It's not found in arid biomes such as deserts.
Like ordinary clay, the block can be mined with a shovel, and unless the shovel has the Silk Touch enchantment on it, doing so will drop 4 Etruria Marl Balls. These balls can be fired in a furnace, or turned back into an Etruria Marl block.