Determining the Provenience of Garnet Beads Using LA-ICP-MS

Abstract

Stone and glass beads have been found at Iron Age (500 BC-AD 500) sites across Southeast Asia and are often assumed to be indicators of contact with South Asia. However, recent research on glass, agate, and carnelian beads indicates there may have also been local production of these materials (Bellina 2007; Lankton and Dussubieux 2006; Theunissen et al. 2000). In Cambodia, two different types of garnet beads have been identified at several Iron Age sites. The first type is spherical, well polished, and appears to have been drilled with a diamond drill, a drilling technique that is strongly associated with Indian bead production (Kenoyer and Vidale 1992). The second type of garnet bead is unpolished, unshaped, and drilled using an unknown drilling technique. Based on these initial differences, it was hypothesized that there were two different bead-making traditions represented amongst the garnet beads, and that the second type of garnet bead may have been locally produced. To investigate this question more thoroughly the garnet beads were analyzed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in order to determine their chemical composition. Geological source samples from a variety of garnet sources across South and Southeast Asia were also analyzed using LA-ICP-MS. Results indicate that LA-ICP-MS is an excellent tool for differentiating between garnet sources and analyzing archaeological garnet artifacts with minimal damage. Furthermore, the results of the study confirm that the two types of beads were made from distinctly different garnet sources, although the location of these sources is still unknown.