STONE OF A GOTHIC PIETA FROM TORUŇ (POLAND)
Center for Higher Education Studies, U Lužického semináře 13, 118 00 Praha 1 - Malá Strana, Czech Republic, e-mail: email@example.com
A comparative microscopical, chemical, and porosimetrical studies confirmed that stone of a Gothic Pieta dated back to the second half of 14th or the beginning of the 15th Century, coming from Nowe Miasto Lubawskie now stored in Toruň (Poland), is identical with a „Prague’s opuka “Plänerkalk” - spongilite or marly chert. This rock consists of about 47 % fine globules of poorly crystallized quartz, 30 % micritic calcite with a few foraminifer tests and 20 - 25 % clay minerals (kaolinite, illite and mixed-layer illite - smectite and scarce glauconite) with a small admixture feldspars, pyrite and fine sandy - silty quartz grains.
The stone was quarried on the outskirts of Medieval Prague in quarries of the area of Strahov - Bílá hora, which are not at present time accessible. Thus a provenance identification can only be carried out with stones from an active quarry nearby village Přední Kopanina, about 10 - 15 km westward of the mentioned Medieval quarries. There is 1,2m thick bed at the bottom of a profile called „golden/red“ or „white“ opuka, which could be used for this comparison.
Although the yellowish color, texture and macroscopic appearance, chemical composition and physical parameters are very similar to the stone from the layer called „golden/red“ opuka, the results of mercury porosimetry show almost an identical resemblance with the „white“ variety of opuka, forming a bottom of Turonian marly cherts.
All data about mineralogy, chemical composition, physical and mercury porosimetry collected by Konta (1993), Scholle, Konta (1987) and the present author (Šrámek, 1997,1998; Šrámek et al., 1992) can be used for future revisions of insufficiently identified stone of many Gothic statues in Austria or Germany.