Origin of the Harappan Ernestites: Fabrication and Raw Materials

Milan Kumar Mahala, Jyotiranjan S. Ray, Alok Kumar Kanungo, G. N. S. Sree Bhuvan, Anirban Chatterjee, Bivin Geo George, Nilanjana Sorcar, Y S Rawat, Jeewan S Kharakwal, S V Rajesh

Significant developments in stone bead technology in South Asia, including drilling techniques, happened during the Harappan civilization. Among the stone drill bits used for bead making, long and constricted cylindrical drill bits made from a unique stone named Ernestite were exclusive to the Harappan civilization. Most Ernestites have been discovered in the Harappan cities in Gujarat, India. The origin of Ernestite remains a mystery without a natural analog and unknown manufacturing process. Here, we present the results of a detailed textural, mineralogical, geochemical, and Sr-Nd isotopic investigation of Ernestite stones and drill bits from three Harappan sites and one Sorath Harappan site in Gujarat carried out to understand their manufacturing process and establish the provenance of the raw materials used. 87Sr/86Sr and εNd(0) genetically link the drill bits to the Ernestite stones. The texture, pseudomullite (aluminosilicate with SiO2 > 40 wt%) matrix, and high substitutions of Al2O3 (> 10 wt%) and TiO2 (> 30 wt%) in hematites point to Ernestites’ synthetic origin via a sintering process, with the temperature reaching ~1100°C. The abundant sand-to-silt-sized detrital quartz and detrital hematite, ilmenite, rutile, and zircon suggest that the Harappans used crudely powdered sandstones and laterites as raw materials. The major oxide contents (SiO2 > 40 wt%; Al2O3 > 20 wt%; TiO2 > 1 wt%), Primitive Mantle-normalized trace element patterns, and Sr-Nd isotopic compositions (87Sr/86Sr > 0.731 and εNd(0) > -18.3) of the Ernstite whole-rocks not only support sand-laterite mixtures as basic ingredients but hint at a regional provenance for the raw materials, within the Kutch region of Gujarat.