Provenance and composition of unusually chrome and nickel-rich bucket-shaped pottery from Rogaland (southwestern Norway)

ABSTRACT We report results from FE-SEM-EDS, geochemical and mineralogical analyses and Raman spectroscopy of pottery of bucket-shaped ceramic from Rogaland (southwestern Norway) dated between the 5th and 6th Century. The study reveals a very rare pottery composition including serpentine-group minerals and an unusual enrichment in compatible elements like Cr (8-27 x normal shale), Ni (2-8x normal shale) and Co (2-3x normal shale). XRD and Raman spectroscopy could pinpoint that Ni is introduced by a specific Ni-rich serpentine mineral and Cr occurs in a rare Cr-rich talc, both minerals are the most abundant in the pottery, which is supported by strong enrichment in Mg (10-20x normal shale concentration). The addition of Mg, Cr, Ni and Co and other compatible trace elements is to our current knowledge not caused by anthropogenic activity but related to the used materials, which are weathering products of mafic and ultramafic rocks. Rocks of this type are exposed in vicinity of the sampling areas in a region called Karmøy, hosting a world famous ophiolite complex, which is identified as the major source for the mafic and ultramafic component, as the next succession of a similar composition is far further north located in Norway and a number of rock types on Karmøy matches the chemical composition of the pottery. The here reported composition is spectacular and extremely rare - if ever found - in pottery. Our study points out that as well unusual material sources have been used for pottery, and it can be speculated if these selections have been made by the manufacturers deliberately, expressing a specific social function, or not – however, sufficient ‘ordinary’, possibly more functional, clay sources have been abundant in Rogaland during time of manufacturing.