An often isolated outcrop of high-quality rock in Europe during the Neolithic period. These sources were exploited for the production of polished stone axes and this became an important industry of the time. The tools were roughly flaked at the factory sites and traded, either as blanks or as finished axes. There were many ax factories in Britain's highlands, northern Ireland, and northwest France. Microscopic analysis is used to identify the rocks by their distinctive crystalline structure, which has enabled the trading networks to be reconstructed.