That hollow is what classifies it as a bullaun stone, a type of boulder with one or more cup-shaped depressions ground into its surface, found across Ireland and often associated with sacred or ritual sites. What makes this particular example quietly peculiar is the combination of what it is, where it ended up, and the likelihood that it was not always there.

The stone is a compact, roughly squared boulder measuring about 0.7 metres in each dimension, with a well-defined oval hollow roughly 27 centimetres long and 10 centimetres deep at its centre. Local tradition holds that it was moved from a spot one to two metres to the north-east of the tomb and pressed into service as a makeshift barrier against livestock at the entrance, a thoroughly practical fate for an object with probable ritual origins. The antiquarian T. J. Westropp visited a holy well roughly 360 metres to the north in 1916 and noted a bullaun stone there, describing a small oval rock basin some 22 inches by 18 inches across and perhaps 13 inches deep. By the time Ruaidhri De Valera and Seán Ó Nualláin carried out their survey of the area in the 1950s, no bullaun stone remained at the well. Whether it was moved deliberately, repurposed opportunistically, or simply shifted during some forgotten episode of land management is not known, but the measurements Westropp recorded are close enough to those of the Ballyslattery stone to raise the question of whether they are one and the same. That identification remains uncertain. What is clear is that the stone is sandstone in a landscape of limestone, making it a geological outsider as well as a displaced one. The holy well, the bullaun stone, and the wedge tomb all sit within the former demesne lands of Newgrove House, a now-vanished country estate recorded on the Ordnance Survey historical mapping of the area.