What the collapse exposed is an 8.5-metre deep vertical vein of boulder clay set within red sandstone bedrock, and it is packed with crystals. Locals call the most prized of these "Kerry Diamonds", a name applied to amethyst found here in considerable quantity. The term mine is informal rather than industrial; no organised extraction took place in any recorded sense, but the site has clearly drawn people's attention for a long time.

The boulder clay itself is glacially derived, meaning it was deposited during the last ice age when glaciers ground across the landscape, collecting and mixing materials from a wide area before dropping them as they retreated. That origin explains the unusual variety of what turns up here: alongside the quartz, rock crystal, and amethyst, the clay also contains jasper, chert, pebble flint, feldspar, and greenstone. Michael Connolly, in his 2008 doctoral thesis on the prehistoric settlement of the Lee Valley near Tralee, noted that this mix is significant beyond its curiosity value. Excavations in the Tralee area have turned up large numbers of rock crystal artefacts, and Connolly suggested that Ballydunlea, with its accessible concentration of raw material, may have been where prehistoric people came to gather or extract that stone. If so, the site connects a striking natural feature to a much longer human story, one in which a gleaming crystal pulled from a clay vein eventually became a worked tool or object in a settlement some distance away.