Study of green-coloured gems of the Roman period from the collections of the Archaeological Museum of Thessaloniki (Greece) and their possible geographic origin

The study of gems in jewellery of the Roman period from known archaeological contexts may provide valuable information for the trading routes of gems in antiquity, the techniques of their manufacture and decoration, the popularity of certain gems or their relation to a specific type of jewellery. Moreover, by the correct identification of these gems, the museum will better inform its public. In the present work, 19 green-coloured gems, which were integral parts of 14 Roman jewellery pieces, dated between the first and fourth century CE, from the collections of the Archaeological Museum of Thessaloniki in Greece, were studied. Most samples were found during rescue excavations in western and eastern Roman cemeteries of Thessaloniki, while one was found in Edessa, a city in northern Greece. All samples were investigated by using strictly non-destructive techniques, for example, optical microscope as well as Raman and Vis-NIR mobile instruments. For the chemical characterisation of the samples, micro-EDXRF was used. Seventeen samples were identified as natural emeralds with characteristics similar to emeralds that originate from Egypt. Among the studied samples, a natural chrome chalcedony and an artificial glass were also identified. The geographic origin of the artificial glass is unknown and that of chrome chalcedony is under discussion with Turkey being the most possible source.