Bath Stone is an Oolitic Limestone comprising granular fragments of calcium carbonate.
During the Jurassic Period (195 to 135 million years ago) the region that is now Bath was under a shallow sea. Layers of Marine sediment built and individual spherical grains were coated with lime as they rolled around the sea bed forming the Bathonian Series of rocks. Under the microscope, these grains or ooliths (egg stone) are sedimentary rock formed from ooids, spherical grains composed of concentric layers.
Bath Stone was mined underground at Combe Down and Bathampton Down Mines, in Somerset; and as a result of cutting the Box Tunnel, at various locations in Wiltshire, including Box and Corsham.
Some of the quarries and mines from which the stone was extracted continue to operate in the 21st century but on a smaller scale than previously; however the majority have been converted to other purposes or are being filled in.
Current examples of re-use include primarily defence establishments, but also a wine cellar at Eastlays (near Gastard) and storage for magnetic media (for Off-site Data Protection) at Monk's Park (near Neston).
Bath Stone has been used extensively as a building material throughout southern England for churches, houses and public buildings such as railway stations.
Originally obtained from the Combe Down and Bathampton Down Mines under Combe Down, Somerset, England, its warm, honey colouring gives the World Heritage City of Bath its distinctive appearance. An important feature of Bath Stone is that it is a freestone, that is one that can be sawn or 'squared up' in any direction, unlike other rocks such as slate, which forms distinct layers.
Bath stone was used long before Ralph Allen promoted its use in Bath in the early 18th century, including his own mansion at Prior Park. Examples include religious, residential and industrial buildings. The Royal National Hospital for Rheumatic Diseases, which was founded in 1738, was designed by John Wood the Elder and built with Bath stone donated by Ralph Allen. It is a Grade II listed building. There is a fine pediment, in Bath stone, on the building depicting the parable of the Good Samaritan.
St Stephens church situated on Lansdown Hill in Bath was constructed from a limestone sourced from the Limpley Stoke mine which is situated in the Limpley Stoke Valley. It has recently been restored.
Claverton Pumping Station at Claverton which was built of Bath Stone around 1810, pumps water from the River Avon to the Kennet and Avon Canal using power from the flow of the River Avon.
The Dundas Aqueduct, which is 150 yards (137.2 m) long with three arches built of Bath Stone, with Doric pilasters, and balustrades at each end.
Much of Bristol Cathedral was built of Bath Stone and the Wills Tower, which is the dominant feature of the Wills Memorial Building, is reinforced concrete faced with Bath and Clipsham stone. Bristol's Cabot Tower was also faced with Bath Stone. Arno's Court Triumphal Arch was built from Bath stone around 1760 and later dismantled before being moved to its current location and rebuilt.
In London the neo-classical Georgian mansion Lancaster House was built from Bath Stone in 1825 for the Duke of York and Albany, the second son of King George III. The brick of Apsley House was fronted with Bath Stone, and several churches including Church of Christ the King, Bloomsbury were built from the material. Apsley House, town house of the Dukes of Wellington , was remodelled in Bath Stone by the 1st Duke.
In Reading the original building Royal Berkshire Hospital of 1839, together with the wings added in the 1860s, are now listed grade II. Reading and Chippenham railway station buildings were constructed for the Great Western Railway in Bath Stone.
Other mansions which have used Bath Stone include: Gatcombe Park, Goldney Hall, Tyntesfield, South Hill Park, Spetchley Park.