It measures just 22 centimetres high and 21 centimetres wide, barely larger than a hardback book, and only five centimetres thick. Yet cut into its face is a single-lined equal-armed cross, precise and deliberate, placed at what appears to have been the centre of the original slab.

The stone is a fragment, one curved edge surviving to suggest that the full piece may once have been subcircular, a disc-shaped slab with the cross positioned at its heart. Such cross-inscribed slabs are among the most common early medieval grave markers found at Irish monastic sites, simple in form but carrying considerable religious weight. Inishcaltra itself, also known as Holy Island, was an important early Christian foundation, and St. Caimin's church is one of several ecclesiastical structures that survive there in varying states of completeness. The island contains one of the more intact groupings of early medieval monastic remains in the west of Ireland, and this small fragment is one of many carved stones that have accumulated within and around its buildings over centuries.