Limestone has been formed over thousands of years and is an important Reagant in Hades 2, especially as it is used to unlock specific spells at the Cauldron at the Crossroads, most of which you will definitely need.

It's important to have enough of them to unlock Incantations with certain perks and benefits during your Hades 2 playthroughs, but collecting them can be a challenge.

You can get Limestone in Oceanus in Hades 2. This is the area you enter after defeating Hecate and her ordeal. Unlike Silver, which looks like a mining node, Limestone is a pile of cream-colored blocks. It can be easily missed, so make sure to loot every level, even the very first one, because it can blend into the background.

You can’t just pick it up, though; Limestone blocks require a Crescent Pick to get Limestone. If you don’t have the pick equipped before the run, you won’t be able to switch to this tool halfway through, meaning you’ll have to finish the run, find the exit or die, then return to the Crossroads, equip the Crescent Pick, and go again.