Bournonite with quartz

With its large, silvery ‘cog-wheel’ crystals, this is one of the finest bournonites in the world. It is a lead copper antimony sulphide, a member of the sulphosalt group of minerals. The miners who extracted it thought the notched crystals resembled cogs, so they called bournonite ‘cog-wheel ore’.

It was collected sometime between 1858 and 1868 by Richard Talling from a vugh (cavity) in the upper levels of the Herodsfoot Lead Mine in Cornwall, where the best specimens in the world were found, and was sold to the British Museum.

Albert Chapman saw this bournonite at the British Museum of Natural History in 1973 (now the Natural History Museum since 1992) and immediately began negotiations to acquire it. The Museum was unwilling to part with it but after the Keeper of Minerals saw the fine specimens that Albert offered in exchange (including Broken Hill alabandite and Tasmanian crocoite), they relented.