engleski

Investigation of chlorite schists (pietra ollare) by IR-spectroscopy and thermal analysis

Vessels made of different varieties of pietra ollare, ultramafic rocks affected by low grade metamorphism, showing characteristic tracks of the manufacturing by means of a lathe have been found at several localities along the Croatian Adriatic coast. In recent years chlorite-schists varieties found in Roman villa rustica in Červar Porat located close to the town Poreč (Istria peninsula, Croatia) have been studied in order to determine their provenance i.e. to determine ancient trade routes. Adequate raw materials for production of the vessels can not be found in Istria and its nearest surroundings therefore import of this kind of vessels should be presumed. This kind of material could be found in Dinaridic ophiolite zone, but there is no evidence in the literature for the use of this material for production of stone vessels, therefore the investigated material most probably has Alpine origin in some of the main production centers of the ancient times. Hence in order to make database of possible source rocks chlorite rich pietra ollare samples were collected in Valli di Lanzo, Valle d’ Aosta, Valchiavenna and Val Malenco, localities known as important production centers of pietra ollare in Italian Alps. Pietra ollare provenance studies performed so far were based mainly on petrographic characteristics, chemical composition and recently on X-ray powder diffraction data. The aim of the present study was to determine if IR and TG, DTG studies could be used to distinguish samples originating from different localities. The obtained results showed that samples from different localities have dissimilar IR-spectra, due to different Mg for Fe and Al for Si substitutions. IR spectroscopy proved as valuable complementary method in the provenance studies of pietra ollare artefacts made from chlorite schists.

archaeometry; pietra ollare; chlorite; IR-spectroscopy; thermal analysis

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