Origin of the Harappan Ernestites: geochemical insights into provenance and fabrication

Advancements in stone bead technology, particularly in drilling techniques, emerged during the Indus Valley (Harappan) civilization. Long-constricted cylindrical drill bits, made from a unique stone called Ernestite, were a distinctive feature of this culture. The origin of Ernestite is a mystery due to the lack of a natural analogue and an unknown manufacturing process. This study presents a mineralogical and geochemical investigation of Ernestite stones and drill bits from several Harappan and contemporaneous sites in Gujarat, India, to uncover their origin. The isotopic ratios of Sr and Nd link the drills to the Ernestites. The texture and presence of pseudo-mullite (SiO2 > 40 wt%) with high Al-Ti-bearing hematite suggest that Ernestites are synthetic, created through a sintering process at ~ 1100°C. An abundance of sand to silt-sized detrital quartz, along with Fe-Ti-Zr-rich minerals, indicates the use of crudely powdered sandstones and laterites as raw materials, with geochemical ties to regional sources.