An atypicality index has been used to compare the chemical compositions of 11 British prehistoric implements (axes and axe-hammers, and a mace) with previously suggested and likely sources in South Wales (Group XIII spotted dolerite from the Carnmenyn area, and Group VIII rhyolite from Carnalw). Atypicality indices together with mineralogy indicate that only two out of six supposed Group XIII implements are likely to be Group XIII, and only one of the five rhyolite implements is likely to originate from Carnalw. These results provide statistical support for earlier provenancing of seven of the implements, and provide the first geochemical source information for four implements. The results illustrate the usefulness of the atypicality index in archaeology, and support the idea that Groups XIII and VIII comprise a larger variety of chemical types than previously thought. Further work is now needed to determine how prevalent this variety is within these implement groups.