A survey of British metamorphic hone stones of the 9th to 15th centuries AD in the light of potassium-argon and natural remanent magnetization studies

Hone stone trade and use during the period of Scandinavian-English interaction (9th–15th centuries AD) was dominated by two metamorphic petrological types represented by the “Norwegian Ragstone” (NR) a quartz-mica schist, and the “Purple Phyllite” (PP) a quartz-mica phyllite, and finds are abundant throughout the Viking world. Petrology associates the NR type with the known quarries at Eidsborg, southern Norway, and this has been endorsed by isotopic evidence. The source of the PP type remains unknown, but has been postulated to be a second facies of Eidsberg material, or even a Variscan phyllite from Belgium. It was the purpose of this study to further refine the possible source area of the PP material. Age data now indicate a “Caledonian” source for the PP type. Within Europe the superposition of metamorphic belts has led to the occurrence of both schist and phyllitic metamorphic lithologies. Petrological criteria therefore rarely provide evidence of the source of such rocks. The zonation of Europe by metamorphic belts does, however, allow isotopic age studies to be used as an aid to provenancing. The PP hones exhibit a range of mineralogy which may indicate a variety of sources, although no archaeological sites capable of producing such a quantity of material have been identified within the Viking world. The evidence, however, indicates a source in the Norwegian Caledonides.