It is an earthfast boulder, meaning it is set directly into the ground rather than placed by human hands, and its roughly flattened western top made it serviceable as an altar surface. Two crosses have been carved into the stone: a plain one on the upper western face, measuring around 20 by 13 centimetres, cut in shallow grooves and shaped in part by working along the natural white vertical striations already present in the rock; and a second, smaller cross on the northern face, only about 11 by 9 centimetres, scratched in two very narrow incised lines. An iron cross leans against the boulder's south-western side, and a few rough stones have been placed nearby, not quite forming a path but suggesting repeated, purposeful approach.

Mass-rocks are outdoor altar stones used by Catholic communities in Ireland during periods when the public practice of the faith was prohibited under the Penal Laws. They tend to occupy marginal, out-of-the-way spots, and this one fits the pattern well: low-lying, screened by a tree to the south, and tucked between a ruined church 170 metres to the north and Tobersenan holy well on the opposite shore of the lake. A stone found at the water's edge roughly 30 metres away, bearing three crosses and the date 1655, places the likely use of this site in the Cromwellian period, when Catholic worship was actively suppressed following the Parliamentarian conquest of Ireland. That datestone is now held in Clare Museum. Clonlea church itself, and the holy well dedicated to a local saint, suggest the area carried religious significance well before the seventeenth century, and the clustering of these sites around a single lake is quietly striking.