It is horseshoe-shaped, about 1.5 metres high and 3 metres long, and it may be a fulacht fia, though no excavation has yet confirmed it. That quiet uncertainty is part of what makes it interesting.

A fulacht fia is a type of prehistoric cooking site, typically identified by a horseshoe or crescent-shaped mound of burnt and fire-cracked stone, the accumulated debris from repeatedly heating rocks and dropping them into a water-filled trough to bring it to the boil. They are among the most common prehistoric monuments in Ireland, found in their thousands, and they date mostly to the Bronze Age. The example on Coney Island fits the general profile in shape and setting, placed close to water on low-lying ground, but as O'Sullivan and colleagues noted in their 2010 survey of the island, without further investigation it remains difficult to classify with certainty. The island itself sits in the Fergus Estuary in County Clare, the stretch of water that feeds into the Shannon just east of Loop Head.