This emerald is used to get Hyper Pot Platinum. 1st you need Reborn arrow then DIO's diary and the hyper chaos emerald.
HOW TO GET:
You need to purchase a trowel from the shop, then try diging until you get it. A trowel has only 3 uses, so be careful. It took me 8 trowels to get it.
It can also spawn around the map, but the spawnrate isnt yet confirmed. all that's known is that it spawns under an hour, since i found it most frequently then.