Portland Roach Stone
Quality building stone
This section of cut roach stone is packed with bivalves and gastropods. Look very closely and you can also just about see the minute egg-shaped ooliths (grains) that make up Portland Stone and help create its quality as building stone. Ooliths form from grains of sand and shell fragments rolled about in a warm sea. Layers of calcium build up over them to form the spherical ‘ooid’. Portland Stone is made of millions of these minute structures, so the rock is a bit like a fish roe. This allows it to be cut or carved in any direction; an essential quality of a building stone.
The roach is a decorative stone and is also very strong, but it is less favoured by architects because of the difficulty in supplying consistent blocks with a similar texture. It was used in the rebuilding of the Cobb (the harbour) in Lyme Regis following the Great Storm of 1824. It’s also used in a very solid bench outside Euston Station in London.
Find out more on the rocks and pseudofossils pages.