Mintaro Slate is produced from what is believed to be the oldest continuously operating quarry in Australia. The quarry was opened in the early 1850s, after Mintaro farmer Peter Brady discovered outcrops of slate in a creek bed on his property and extracted slabs suitable for building his homestead. Amongst its many uses and qualities which have been exploited in the years since then, the perfectly flat surface of Mintaro Slate most famously makes it ideal for constructing the tops of billiard tables. The open-cut slate quarry is located 1.5 km west of the township of Mintaro. Dimension stone slate and flagstone quarried at Mintaro is known geologically as the Mintaro Shale, a Neoproterozoic fine-grained sedimentary unit formed near the top of the Burra Group, which was deposited on the sea floor within the Adelaide Geosyncline under low-energy conditions ~800 million years ago. At the type section defined near Clare, the measured thickness of Mintaro Shale strata is 1 km, compared to 800 m at Mintaro (Preiss, 1987). The Mintaro quarry's several workings are located in a zone of broad, open folding, with bedding at the site that is being quarried presently dipping at 17–18º to the west. In physical terms, Mintaro Shale is a grey, evenly bedded, finely laminated metasiltstone or proto-slate with minor dolomitic siltstone interbeds. Grain size of the rock varies from 0.03 to 0.3 mm. It lacks a well-developed metamorphic slaty cleavage, which therefore precludes it from being properly classified as a slate type rock. However, the natural joints and fractures present in the unit at the quarry location are smooth, narrow and widely spaced, and facilitate the mining of large slabs. Remarkably uniform bedding allows the slate to split cleanly. From 1995 to the end of 2004, reported annual output of the quarry has varied from 654 t in 1997 to 1412 t in 2002, with an average of 930 t. Markets include all states of Australia, Japan, Hong Kong and New Zealand. Products include billiard table tops, kitchen and laboratory bench tops, fireplace hearths, doorsteps, tiles, verandah edging, paving flagstones, headstones, and random garden and driveway paving. Earlier uses were cricket pitches, troughs, tanks, vats, urinals, animal feed and water troughs, switchboards and blackboards. In-ground resources are sufficient to maintain production at the present rate of extraction for many years.