I usually just crack open Magma Geodes dropped from breaking Rocks on Floors 81-119 in the Mines but some people with an upgraded Hoe like to till dirt in the Mines on Floors 40-79 to get the drop that way.
I usually just crack open Magma Geodes dropped from breaking Rocks on Floor 81-119 in the Mines but some people like to Till the mines in floors 40-79 to get the drop that way.
The Wiki says, it can also be gathered from Artifact Troves, since it is one. Magma Geodes and Troves have better chances, around 3,5 or 3,8%, to have one inside.
Yeah artifact troves are the best bet, and to get them just trade omni geodes at the desert trader.
If you don't already have a hoard of geodes you're best off monster musk/burglar and killing ghosts in skull cavern, just breaking rocks with excavator is fine too but killing monsters is really fast and you'll get a few hundred a day at least. You can make your ghost slaying faster by making a good dagger and putting crusader on it, use the special on the ghosts and it doesn't immediately knock them back.