Limestone, carbonate rock, Cotham marble var. This is a specimen that should not be in my mineral collection. It could be included in my rock collection, or my fossil collection. It is not a true marble, but a limestone, and is a localised variety restricted to south Wales and west of England The patterns in this semi polished specimen from Cotham, near Bristol have been created by the upward growth of algae and worms, and are about 200 million years in age.