Cornish slate has been used as a building material for well over 600 years, and has been quarried continuously since the early 17th century. In general it has been used as paving, walling and decorative purposes, however in the area around Delabole in the north west of Cornwall is it of sufficiently high quality to be used for roofing. In the early 19th century there were many small quarries in the area, five of which joined to form the Old Delabole Slate Company. At a time of a general downturn in slate production the company was liquidated in 1977 and changed ownership several times The Delabole Slate Company is now owned by the Hamilton family. The present quarry encompasses the original five quarries and is now 800m x 6000m in area and 140m deep. It is located close to the village of Delabole.
Roofing slate is also produced from the Trevillet Quarry Trevillet,Tintagel. This quarry is owned by Mill Hill Quarry Ltd. Tavistock Devon. The company was established in 1959 when the disused Mill Hill quarry (SX452750) was reopened. The company acquired Longford Quarry in 1984, and the Trevillet Quarry in 1990 However only the Trevillet Quarry produces roofing slates.
The Delabole and Trevillett quarries are located in the Delabole slate bed formation. The original deposits, which make up the formation, were laid down in the Upper Devonian over 360 million years ago and metamorphosed during the Hercynian Orogeny approximately 300 million years ago. The slate is a blue-grey colour and very durable and is still found locally on buildings over a hundred years old.