A chest tomb is a free-standing box-shaped funerary monument, typically raised above ground level and decorated on its sides with carved panels, and this fragment is composed of fossiliferous limestone, a stone whose surface carries the visible remains of ancient marine organisms pressed into the rock itself.

The discovery was made during investigations by Cóilín Ó Drisceoil in 2019. The fragment had effectively been recycled as building material when the arcade bay was blocked up in 1740, a practice not uncommon in Irish ecclesiastical buildings where earlier carved stonework was pressed into service for repairs or alterations. St Mary's is one of Kilkenny's older parish churches, and the presence of high-quality carved funerary stonework is consistent with the town's long tradition of elaborate stone carving, fed in part by the availability of the local black limestone. The fragment is currently held in storage in the north-east corner of the south side of the graveyard, rather than on display or in a museum setting, which means it occupies a quiet, unannounced spot within the churchyard grounds.