Applicability of Samarium-Neodymium isotopy

Applicability of Samarium-Neodymium isotopy for provenancing Viking age steatite

Tobias B. Skowronek

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Steatite, also known as soapstone, is a raw material used by many cultures throughout the human history its usages being manifold. However, up until now there is still no generally valid strategy to assign archaeological objects made from this particular material to a specific steatite deposit. Thus new applications with the aim to establishing a geochemical fingerprint are pivotal. A pilot study highlighting the potential of 147Sm/144Nd isotopy can usefully be executed in a Viking-age context: Steatite vessels are regarded as one of the characteristic features of Viking material culture present in both Atlantic settlements and Scandinavian homelands. However, the sources of the archaeological steatite found at the above mentioned localities remain to be observed. Solving the question of origin of the well-dated Ribe, Dk steatite can contribute to the understanding of the development of commerce and urbanization at the very beginning of the Viking period.

Archaeological background to the project

Steatite, also known as soapstone or in danish: fedtsten, has been a material known to Scandinavians since the stone age (Skølsvold, 1961). During the Viking Age, quarrying and working of steatite became major industries because the handy material is suitable for all kinds of domestic needs (Jesch, 2015). Therefore, steatite goods were found in great quantity at emporia like Hedeby or Ribe. Heid G. Resi was the first to look at the massive corpus of steatite finds from Hedeby (Resi, 1979). Resi argued that these steatite finds must have come from either western Sweden or eastern Norway. The results of mass spectrometry and cluster analysis conducted by Björg E. Alfsen and Olav H. J. Christie (1979) supported this idea. Because of the huge amount of steatite at Hedeby and the wide distribution of the latter in Denmark Resi argued that Hedeby may have served as a distribution point for the whole of Denmark. This however, now seems to be questionable.

Different types of soapstone fragments from Oslogate 6, medieval Oslo. Photo: Guro Koksvik Lund
Different types of soapstone fragments from Oslogate 6, medieval Oslo. (Photo: Guro Koksvik Lund, Museum of Cultural History, University of Oslo)

The study of networks and nodal points in early Viking-age Scandinavia by Søren Sindbaek (2007) suggests that Hedeby indeed may have received commodities from western Sweden and from emporia like Kaupang in eastern Norway but it seems unlikely that those commodities were also forwarded to Ribe. It is more likely that Ribe received its steatite from elsewhere in Norway maybe from Agder (especially the area around Fjaere) via the medieval port of Hesnessund or from western Norway (Schou, 2017).

The important thing to learn about the goods and products is the degree to which they are standardized and routinized. Did the steatite at Ribe come from only one region or is there evidence that all major deposits are represented? Does this follow political boundaries, like the southern part of Norway was often linked to or controlled by the Danes? Were certain types of objects only made of steatite from a single region, for instance particular bowl forms? All of these questions will contribute to the understanding of the organization of the industry and the role Ribe played in the development of commerce and urbanization at the start of the Viking period. Therefore the question of steatite provenance here is pivotal.

Methodology and preliminary studies

Prior attempts on sourcing steatite have focused on whole-rock chemistry using XRF or Rare-Earth Element determination with more or less convincing results (e.g. Jones et al., 2007, Hansen et al., 2017). Prior studies of the applicant have revealed that instead of focusing on the composition of the steatite itself the chemical characterization of the precursor ultramafic rock yielded promising results (Skowronek et al., 2020). Keulen et al., (2022) took the idea further and applied 147Sm/144Nd isotopy on steatite of Greenland revealing a similar potential since the isochron age of the latter rocks was interpreted as the age of metasomatism that had affected the precursor rock. Nd seem to be rather immobile during metasomatism. Thus, 147Sm/144Nd may act as dating tool for the ultramafic protolith and possibly presents a fingerprinting possibility equivalent to lead isotopy as used in Archaeometallurgy. The Viking-age steatite of Ribe is highly likely to be from Norway. Given the variety of tectono-metamorphic regions in Norway (see Fig. 1) an assignment of an archaeological sample to one or more of these regions could be possible. The Norwegian geological survey (NGU) has agreed on collaborating in this project with sharing their extensive XRF data on Norwegian steatite deposits. This will help to further differentiate between sources.


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