TRACE ELEMENT COMPARISON OF ANCIENT ROMAN INTAGLIOS AND MODERN SAMPLES OF CHROMIAN CHALCEDONY; AN ARCHAEOGEMOLOGICAL PROVENANCE STUDY

The trace element chemistry is compared from the chromian-chalcedony intaglios of Ancient Roman era to the modern samples that are collected in NW Turkey. Twenty ancient intaglios dated between 100 AD to 300 AD of Roman era stylistically. The intaglios are later set in a gold necklace in the 19th century. The modern samples are collected by one of the authors (CL) in Saricakaya, Eskisehir, NW Turkey in 2007. A Laser ablation-inductively coupled plasma mass spectrometer (LA-ICPMS) system was used to determine the concentrations of trace elements in both the ancient and modern chromian-chalcedony samples. The system used in this study is a Thermo X-series II quadrupole ICPMS coupled with a New Wave Research UP-213 laser ablation system. The laser conditions were set to a 55 micrometer spot in diameter, laser is running at 7 Hz repetition rate with a fluence around 10 J/cm². The ICPMS was running at 1300 W forward power and was tuned to a condition that maximizes beryllium counts while keeping ThO/Th ratio less than 2%. NIST SRM 610 and 612 as standards are used in a typical run, three spots on each standards were run before the actual sample and three additional spots on the NIST 610 were added after two samples were run. At the end of the run, three spots on the NIST 610 are collected to correct the instrument shifts. All analysis use ²⁸Si as internal standard for the chalcedony spots. Preliminary results indicated that most elements included in this study showed good agreement between two sample populations.

Chromian-chalcedony from different localities has been studied by several researchers. The first modern occurrence was discovered in Zimbabwe in 1953 and the variety was named Mtorolite. Another source was discovered in the early 1990s in Western Australia. Other chromium-bearing chalcedonies have been reported from sources such as Bolivia, the Balkans, and Ural Mountains. However, none of the modern sources of “chromian- chalcedony” can be associated with the material used in antiquity, either geographically or mineralogically. It has been suggested that the Roman material may have been obtained from the vicinity of chromium mines in Anatolia, Turkey. This study aims to demonstrate the strong similarities between the ancient Roman material and the modern Anatolian Chromian-chalcedony from NW Turkey.