Portland stone

Geology and Formation: Portland stone formed in a marine environment in a shallow, warm, subtropical sea. Seawater releases dissolved carbon dioxide as a gas, forming calcium carbonate. Lime mud accumulated on the sea floor, with particles forming calcite layers. Oolitic limestone formed from billions of calcite balls partially cemented together. Portland stone measures 3.5 on the Mohs scale of mineral hardness. History and Use: Stone quarrying on Portland dates back to Roman times. Extraction as an industry began in the early 17th century. Portland stone was used for St. Paul’s Cathedral in London. Companies like Albion Stone PLC and Portland Stone Firms Ltd have been quarrying the stone since the 1980s and 1990s. Famous buildings like Palace of Westminster and Tower of London built with Portland stone. Quarries, Mines, and Quarrying Methods: Jordans Mine is the biggest mine on Portland, using mining techniques. Bowers Quarry has been operational since the late 18th century. Stonehills Mine is a new mine estimated to last for 50 years. Traditional quarrying methods involved gunpowder and plugs and feathers. Modern methods involve diamond bladed cutting machines and wire saws. Restoration, Preservation, and Memorials: Once quarries are worked, they are restored to their original state. The Portland Sculpture and Quarry Trust is dedicated to preserving stone knowledge. Memorials like the Cenotaph in Whitehall and RAF Bomber Command Memorial use Portland stone. The trust holds workshops at Tout Quarry annually. Tout Quarry, donated by Portland Stone Firms, is a nonworking quarry. Applications, Technology, and Substitution: Portland stone used in various structures worldwide. Italian stone cutting equipment introduced in 1999 improved quarrying methods. Portland stone designated as a Global Heritage Stone Resource. Substitution controversies with Anstrude Roche Claire stone from France. ‘Portland cement’ coined by Joseph Aspdin in 1824, resembling Roman cement.