You can see a superb natural outcrop of Frosterley Marble in the Bollihope Burn at Harehope Quarry, just outside Frosterley in Weardale. The best place to view the Frosterley Marble is from a footbridge on a permissive path at the west end of the quarry.

Frosterley Marble is a layer of dark grey limestone which contains beautiful fossils of the extinct solitary coral Dibunophyllum bipartitum. These creatures had curved horn-shaped skeletons and tentacles which filtered out particles of organic matter from the seawater. When they died, their skeletons collected on the sea floor and were covered by limy ooze which hardened into dark grey limestone. The corals are now visible as white
shapes which show the internal structure of their skeletons in intricate detail.