Stone Grave before and after it's been mined.
The Stone Grave is a makeshift grave made out of stone, distinguished by a large horizontal boulder surrounded by a number of smaller vertically oriented stones. A small rectangular stone can sometimes be found placed in front of these graves, likely as something to place offerings on. It is known as Dolmen in the game files.
These Points of Interest can be found scattered throughout Meadows. When mined, the area has a chance to leave skeletal remains that can be picked up for bone fragments. The treasure chest that is sometimes buried beneath the large boulder can contain various items such as coins, amber, amber pearls, rubies and silver necklaces.
A Skeleton can also spawn with the grave, usually clipping within the large stone.