I have found this large stone in the middle of a wooded area. When I interact with it, It gives me back the message “there is some kind of strange aura leaking out from the…cracks? Are they really just cracks.
I don’t know for sure, as I have not collected all of them but if you check the key items in your inventory, the Odd Keystone that you use to collect all of the purple wisps around the map looks a lot like the stone in the picture you have linked.
Eerie purple light, mysterious stone, strange aura. They all feel like they fit in the same area and sure the icon itself looks just like the large stone. The crack is even quite similar. I am guessing this stone will activate once you have collected all of the wisps in the game.