Viking age honestones from four large sites in northern Europe have been made from two different types of quartz-muscovite schist: one dark grey, very fine-grained schist, and a light grey, fine-grained schist. In order to determine the provenance of these schist hones, potassiumargon ages have been determined on 16 selected representative hones. The dark grey schist hones yield Caledonian ages of 403-446 Ma, and consideration of petrographic evidence leads to the conclusion that the hones were quarried in the Caledonian area (presumably) of westernNorway. The light grey schist hones are Precambrian, with potassium-argon ages of 931-946 Ma, and are presumed to originate from Telemark, south Norway. The amount and homogeneity of these honestone groups from different parts of the Viking world indicate the existence of large quarries, and demonstrate that production and trade were more wide-ranging than had hitherto been assumed.