The boulder is not especially large, roughly 1.1 metres north to south and 1.2 metres east to west, rising to about half a metre at its southern end. But the circular hollow carved or ground into its upper surface, some 30 centimetres across and 13 centimetres deep, is the thing that marks it out.

This is a bullaun stone, a type found at scattered locations across Ireland, typically associated with early medieval religious or ritual activity. The word bullaun derives from the Irish word for bowl, and these basins, cut or worn into natural boulders or bedrock, are thought to have served a variety of purposes over the centuries, from the practical grinding of grain or pigment to uses bound up with healing, cursing, and votive practice. Water collecting in the hollow was often believed to carry curative properties. The example at Carrigeenshinnagh sits earthfast, meaning the boulder is set into the ground rather than freestanding, which is a common feature of the type. Its position on a gentle south-facing slope, immediately north of the boggy ground bordering a stream, follows a pattern seen elsewhere, where bullaun stones occupy liminal spots at the edges of wet or transitional ground.