From the Upper Jurassic, Upper Purbeck beds of South-East Dorset.
The Purbeck beds are essentially freshwater deposits formed within a delta. The Purbeck marble is a mass of freshwater snails, Viviparus (Paludina) and though technically not a marble, it polishes beautifully. Because of its rich colours and textures, it has been sought after and quarried since Roman times. Perhaps its heyday was in the 12th and 13th centuries.
The Purbeck marble can be either green, blue-grey, and shades of red in colour. It's hard and dense, but with some clay in the matrix between the packed shell of the water snail.