Fewer know that somewhere between the ancient oratory and the leacht, a flat stone prayer platform used by the monks for communal devotion, there once stood a carved cross-slab that is now broken, removed from its original position, and held in an Office of Public Works depot on the mainland.

The slab was recorded as standing near the oratory as early as 1875, when the antiquarian Dunraven noted its presence on the south terrace. By the time researchers examined it more closely in the late twentieth century, it had already broken and its lower portion lay flat on the ground. That surviving fragment measures 0.68 metres by 0.43 metres and is 0.15 metres thick. It carries the lower section of an outline ringed Latin cross, the kind in which the arms are enclosed within a circle, with a wide open-ended shaft that would originally have extended upward into the now-lost upper portion. The stone itself has been identified as Valentia slate, a material quarried on the island of the same name nearby in Kenmare Bay, which gives some sense of the local sourcing of materials even in this most isolated of monastic communities. Grellan D. Rourke, who identified the slate type, also produced a reconstruction drawing showing what the complete cross would have looked like, and the slab features in the 1990 study by Horn, White Marshall, and Rourke titled "The Forgotten Hermitage of Skellig Michael".

The fragment is no longer on the island. It passed into OPW care and now sits in a depot, assigned its own separate monument record number that acknowledges its current location rather than its origin. What remains on the island is the context: the oratory, the leacht, the south terrace, and the now-empty spot where the slab once stood upright, marking the devotional geography of one of the most remote early Christian settlements in Europe.