It is a bullaun stone, a type of worked or naturally hollowed boulder associated with early Christian and sometimes pre-Christian practice in Ireland, and its defining feature is a smooth, oval basin ground into its upper face. These basins were used for a variety of purposes over the centuries, from the grinding of pigments or grain to ritual uses connected with holy wells and saints' sites. The water that collects in them was, and in some places still is, considered to have curative properties.

This particular stone is a fairly substantial piece of granite, measuring roughly 84 centimetres by 62 centimetres across and standing about 55 centimetres high. The basin itself is oval, around 50 centimetres at its longest and 28 centimetres wide, with a depth of approximately 16 centimetres, which suggests regular and sustained use over a long period, since that kind of hollow does not form quickly. It sits within the remains of the church at Saintkierans, a site that takes its name from Saint Ciarán, one of the earlier figures in Irish Christian tradition. The association of a bullaun stone with a church dedicated to such a saint places the object within a broader pattern seen across Ireland, where ancient stones were incorporated into, or simply remained beside, early ecclesiastical foundations rather than being displaced by them.