Soapstone as a locally used and limited sculptural material in remote area of Northern Moravia (Czech Republic)

Abstract

In contrast to Nordic countries, talc-rich rocks (massive and schistose talc-bearing rocks—talcite, magnesite-talc schists, chlorite-talc schists, and/or chlorite-actinolite-talc schists often loosely classified as soapstone) represented practically an unknown natural building and sculptural stone in the Czech Republic. This extraordinary material was quarried and used in the only region of the Czech Republic where Sobotin amphibolite massif (Sumperk district, northern Moravia) outcrops. Metamorphosed basic igneous rocks contain small lenses of soapstone that were exploited in the past and used not only for refractory purposes but also as a construction and sculptural material.Occurrences of ‘Sobotin’ soapstone show distinct zone macrofabric marked by the occurrence of massive soapstone in the core that gradually changes to talc-dominant schists, later to actinolite/tremolite-rich schists and finally to chlorite schists at the contact with surrounding amphibolites. The most typical ‘Sobotin’ soapstone exhibits high density (up to 2,900 kg m−3), low water uptake (maximum 0.68 wt %), favorable dynamic elastic properties (P-wave velocity 5,340–5,840 m s−1, S-wave velocity 2,900–3,300 m s−1), and mechanical properties (tensile splitting strength 5.2–6.9 MPa, uniaxial compressive strength 17.5–24.1 MPa). ‘Sobotin’ soapstone is relatively resistant to weathering action although schistose varieties show typical delamination when exposed to frequent freeze/thaw cycling in harsh mountainous environment. Field survey of monuments, architectural and building artefacts made from ‘Sobotin’ soapstone contributed to our knowledge on duration of exploitation of ‘Sobotin’ soapstone that was for sure utilised from the second half of seventeen century till the beginning of the twenty century. The most characteristic feature of ‘Sobotin’ soapstone is its strict local use on the territory of about 20 villages surrounding previously exploited soapstone lenses.