The stone is an erratic, meaning a boulder transported and deposited by glacial activity rather than formed in place, and it measures roughly 1.7 metres along its longest axis. What makes it unusual is not its size but its surface: two deep natural indentations on its northern edge, and a shallow circular depression, about 20 centimetres across, on the top. These hollows, shaped by geology rather than any human hand, were nonetheless read for centuries as something altogether more charged.

According to tradition recorded in the Ordnance Survey Letters of 1836, the indentations mark the impression left by St. Patrick's knee as he knelt in prayer, and the stone's reddish colouring was said to derive from the saint's own blood. The Ordnance Survey Letters were a series of detailed field notes compiled by the survey's officers as they moved through Ireland in the 1830s, gathering local history, folklore, and place-name lore alongside the topographical measurements. That such a tradition was considered worth recording at all suggests it was well established by the time the surveyors passed through. The stone sits within a cluster of related features: a holy well lies roughly 15 metres to the south-west, and a graveyard roughly 25 metres to the north, so the boulder occupies a landscape already layered with devotional meaning, each element reinforcing the sanctity of the others.