The Building Stones from the Vanished Medieval Church at Onarheim, Tysnes, Hordaland County in Western Norway: Provenancing Chlorite Schist and Soapstone

Abstract

This study centres on the provenance of soapstone and chlorite schist building stones at Onarheim church, 50 km south of Bergen and also provides geochemical results that are of key interest in further studies of Norwegian chlorite schist bakestone. The present Onarheim church is made from wood but building stones from previous stone churches at the site (12th century and early 19th century) are found in Foundation walls and the walls surrounding the churchyard. Geochemical analyses (main and trace elements, Sr-Nd isotope composition and rare earth profiles) from such stones were compared with results from similar analyses from a variety of quarries, including reference quarries in Rogaland and Trøndelag (chlorite schist). Unsurprisingly, the nearest soapstone quarry (Baldersheim) and the regional source of chlorite schist (Ølve-Hatlestrand) gave the best matches. However, the results also indicate two additional sources of soapstone, one of them is the distant Arnafjord quarry. This may represent an input of soapstone for postmedieval restoration and/or early 19th century construction works. A very important result of the study was that Sr-Nd isotope ratios distinguish between the known medieval chlorite schist quarries in Norway and different quarries at Ølve-Hatlestrand. Bakestone made from chlorite schist is found all over Norway and the opportunity to fingerprint their origin may aid in future interpretation of medieval trade patterns.