Bath stone

Bath Stone is an oolitic limestone comprising granular fragments of calcium carbonate. 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, England its distinctive appearance. An important feature of Bath Stone is that it is a 'freestone', so-called because it can be sawn or 'squared up' in any direction, unlike other rocks such as slate, which forms distinct layers.

Bath Stone has been used extensively as a building material throughout southern England, for churches, houses, and public buildings such as railway stations.

Some quarries are still in use, but the majority have been either converted to other purposes or are being filled in.

Geological formation

Bath Stone is an oolitic limestone comprising granular fragments of calcium carbonate laid down during the Jurassic Period (195 to 135 million years ago) when the region that is now Bath was under a shallow sea. Layers of marine sediment were deposited, 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 stones) are sedimentary rock formed from ooids: spherical grains composed of concentric layers. That name derives from the Hellenic word òoion for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm. Rocks composed of ooids larger than 2 mm are called pisolites. They frequently contain minute fragments of shell or rock, and sometimes even decayed skeletons of marine life. Bath stone was taken from the Bath Oolite Member and the Combe Down Member of the Chalfield Oolite Formation, part of the Great Oolite Group.