It measures roughly fourteen centimetres high and thirteen centimetres wide, the exposed portion barely larger than a paperback book. What draws the eye, once you know to look, are two incised crosses cut into its face: one equal-armed, with slightly flared or expanded terminals, positioned near the centre, and a second, smaller version pressed into the bottom left corner. The stone is broken, its original shape unknown, but those two surviving crosses carry a quiet suggestion of what the whole may once have been.

Scholars Elisabeth Okasha and Katherine Forsyth, writing in 2001, noted that slabs bearing five crosses arranged with one at the centre and one at each corner were used in early medieval Ireland as altar stones. The standard form would consecrate the four corners and the middle of a flat surface, marking it as sacred for the celebration of the Eucharist. The Toureen fragment, with its central cross and at least one corner cross preserved, fits that pattern closely enough to be catalogued as a probable altar slab, referred to in the literature as Toureen Peacaun 29. It came to light during an excavation carried out in 1944 by Duignan, when the site was systematically investigated, and was subsequently built into the east wall of the church where it remains today, no longer in liturgical use but still embedded in the fabric of the building it once served.