Roman lava quarries in the Eifel region (Germany): geochemical data for millstone provenance studies

Roman millstones of assumed Eifel origin were produced and exported in huge quantities to many parts of Roman Europe and can be used as tracers for trade patterns in Roman times. This study presents for the first time a raw-material centred geochemical definition of the 13 well-known Roman basaltic lava quarries in the Quaternary East and West Eifel volcanic fields. The aim is to find a way to characterize the individual exploitation sites precisely by means of their geochemical composition and to recommend a standard procedure for further millstone provenance analysis. Based on major and trace element composition analyses by XRF, a differentiation of each quarry is achieved by using a combination of geochemical discrimination and cluster and discriminant analysis. Therefore, for provenance analysis of a unknown millstone sample the following procedure is recommended: (1) geochemical discrimination to check if it actually belongs to the volcanic Eifel quarries; (2) cluster analysis to check to which quarry or cluster of quarries the millstone can be affiliated; and (3) discriminant analysis to assign the sample to its quarry of origin with a certain confidence.