During the archaeological excavation carried out at the high Medieval site of Loppio, a white, ring-shaped micro bead was found inside Building I of Sector A, within the filling material of a stratigraphic layer (US 629) that may be dated to 5th/6th centuries AD. Based on the comparison with other prehistoric artefacts found in Loppio and the surrounding areas the bead is likely to be dated ca. 3300-2300 BC. This bead represents a unicum in the Loppio collection. Its size is 4.22 mm in diameter, 1.76 mm in hole and 1.56 mm in height. A program of non-invasive analysis has been carried out to investigate its mineralogical and chemical composition. Optical, ESEM and SEM observations show that the bead has a white interior and a beige surface locally with a glossy appearance. The surface of the hole show no obvious drilling mark. Micro-FTIR and micro-Raman analyses indicate that the bead was made of enstatite, the Mg-rich orthopyroxene. Results of XRD analysis also suggests that the enstatite is not a natural product, but is very likely synthetic. Qualitative EDS chemical analysis shows the presence of O, Mg, Si (with minor Fe), which is fully consistent with the composition of enstatite. The area with glossy appearance show a distinct composition with higher Si, Al, K and Ca contents. Since enstatite is very hard, in the range 5-6 of the Mohs scale, it is very unlikely that it was used as a raw material to carve such small beads. The production of enstatite beads and other artefacts by heating (burning) of steatite (or saponite) at temperatures above 900°C is well documented in the relevant literature. Enstatite (after steatite) beads are described from several sites in eastern and middle-eastern countries and dates to the 7th millennium. Very few information exists on the use of this pyro-technology in the Italian context during prehistory. Very few beads made of enstatite from Italy have been described (although 'steatite' beads are reported from several sites) and we suggest that this may be due to lack of archaeometric investigations. The present work not only provides a detailed chemical and mineralogical characterization of the small enstatite bead found in Loppio, but it also describes a non-invasive analytical protocol that can be easily and economically applied to the investigations of larger collections of similar beads. Our finds can also have important implications on assessing the trade and technological achievments in northern Italy area during the Copper Age.
Perlina anulare di enstatite: caratterizzazione mineralogica e chimica e ipotesi sulla tecnica di produzione e zona di provenienza.
Fioretti A;
2016
Abstract
During the archaeological excavation carried out at the high Medieval site of Loppio, a white, ring-shaped micro bead was found inside Building I of Sector A, within the filling material of a stratigraphic layer (US 629) that may be dated to 5th/6th centuries AD. Based on the comparison with other prehistoric artefacts found in Loppio and the surrounding areas the bead is likely to be dated ca. 3300-2300 BC. This bead represents a unicum in the Loppio collection. Its size is 4.22 mm in diameter, 1.76 mm in hole and 1.56 mm in height. A program of non-invasive analysis has been carried out to investigate its mineralogical and chemical composition. Optical, ESEM and SEM observations show that the bead has a white interior and a beige surface locally with a glossy appearance. The surface of the hole show no obvious drilling mark. Micro-FTIR and micro-Raman analyses indicate that the bead was made of enstatite, the Mg-rich orthopyroxene. Results of XRD analysis also suggests that the enstatite is not a natural product, but is very likely synthetic. Qualitative EDS chemical analysis shows the presence of O, Mg, Si (with minor Fe), which is fully consistent with the composition of enstatite. The area with glossy appearance show a distinct composition with higher Si, Al, K and Ca contents. Since enstatite is very hard, in the range 5-6 of the Mohs scale, it is very unlikely that it was used as a raw material to carve such small beads. The production of enstatite beads and other artefacts by heating (burning) of steatite (or saponite) at temperatures above 900°C is well documented in the relevant literature. Enstatite (after steatite) beads are described from several sites in eastern and middle-eastern countries and dates to the 7th millennium. Very few information exists on the use of this pyro-technology in the Italian context during prehistory. Very few beads made of enstatite from Italy have been described (although 'steatite' beads are reported from several sites) and we suggest that this may be due to lack of archaeometric investigations. The present work not only provides a detailed chemical and mineralogical characterization of the small enstatite bead found in Loppio, but it also describes a non-invasive analytical protocol that can be easily and economically applied to the investigations of larger collections of similar beads. Our finds can also have important implications on assessing the trade and technological achievments in northern Italy area during the Copper Age.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
