It is conglomerate bedstone, the kind used as the lower, stationary grinding surface in a working mill, and it may well have been quarried from a nearby millstone quarry on the same mountain. The fact that it ended up underfoot at a domestic back door tells you a good deal about how this site has been repurposed over time.

The mill itself sits on the south side of Quitrentmountain, a single-storey rectangular structure about twenty metres along its east-west axis, built from random-rubble sandstone. Alongside its east wall is an overgrown wheel-pit, roughly 1.23 metres wide and two metres deep, which likely housed a low breast shot or undershot waterwheel, meaning one driven by water arriving at or below the wheel's centre rather than from above. The millrace, the channel that fed water to the wheel, was drawn from a mountain stream about 300 metres to the north-west. What stands today is actually a reduced version of the original building; the present north wall was once an internal wall within a larger structure that extended further north, and a separate ruined building adjoining the wheel-pit had already been recorded as ruinous on the six-inch Ordnance Survey map of 1903. According to local information, the O'Mahony family, who also built the adjacent mid-nineteenth-century house, owned and operated the site as both a corn and a woollen mill. Operations ceased in the 1920s, and the buildings were subsequently altered by the Land Commission in 1958, most likely the conversion into farm buildings that accounts for the mill's current diminished footprint.

The house immediately to the east has been recently renovated, which makes the contrast with the overgrown wheel-pit and the fragmentary mill remains all the more pronounced. The millstone at the back door is easy to miss if you do not know what you are looking at, but it is a quietly legible piece of industrial history, sitting in plain sight.