The Linkage between garnets found in India at the Arikamedu archaeological site and their source at the Garibpet deposit

The archaeological site of Arikamedu, located in Tamil Nadu State on the east coast of India, was the centre for many centuries of a significant bead-producing industry. Beads were made of both glass and stone, including garnet, but the source of the garnet rough material has not been confirmed. To probe this question, garnet beads found at Arikamedu were compared with rough material from the Garibpet deposit, located approximately 640 km away in Telangana State, east of the city of Hyderabad, India. Samples from the two localities exhibited substantial correlation with respect to average composition, trace-element contents, chemical zoning of major and minor elements, inclusion assemblages and zoning of inclusions between the rims and cores of the crystals. Chemically, the stones were almandine rich (averaging 81.0% almandine, 11.5% pyrope, 3.3% spessartine and 1.5% grossular), with pronounced zoning for Mn and Mg. Zoning of trace elements also was observed, especially for Y, P and Zn. The most characteristic aspects of the inclusion pattern were sillimanite fibres that were concentrated in a zone between an inclusion-rich core and an inclusion-poor rim. In combination, the microscopic observations, identification of the inclusion assemblage, and chemical analyses established that the rough material used historically in the Arikamedu area to produce garnet beads originated from the Garibpet deposit. Furthermore, the results suggest that existing schemes for classifying historical garnets require additional refinement.