Karur is a town and district in the central Tamil Nadu region of southern India, situated on the Cauvery river. The locality is best known in the gem trade for chrysoberyl, including alexandrite and cat's-eye chrysoberyl, recovered from pegmatite-derived alluvial deposits in the surrounding districts of Karur, Erode, Salem and Coimbatore. The Karur material has supplied the Indian and international cat's-eye chrysoberyl trade for several decades and represents one of the principal modern sources outside Sri Lanka.

Geological setting

The chrysoberyl deposits of central Tamil Nadu are hosted in pegmatite intrusions and associated metamorphic rocks of the southern Indian shield, particularly within the Charnockite-Khondalite belt of the South Indian granulite terrain. Beryllium-bearing fluids associated with the pegmatites produce primary chrysoberyl, which is then concentrated in alluvial gravels through weathering and transport. Working in the Karur region has historically been small-scale and artisanal, with material recovered through pit and panning operations along seasonal streams and rivers.

Material

The Karur production includes:

• Chrysoberyl in pale yellow, yellow-green and brown body colours, used for faceting and for cat's-eye cabochons.
• Alexandrite, the colour-change variety, with material from the region showing greenish to greenish-brown daylight colour and reddish to brownish-red incandescent colour. Karur alexandrite generally does not match the colour-change strength of fine Russian Ural Mountain or Brazilian Hematita material, but a fraction of production reaches good commercial quality.
• Cat's-eye chrysoberyl with the silky chatoyancy that defines the variety. The Karur material competes with Sri Lankan production in the international cat's-eye trade and supplies Indian domestic cutters.

Trade context

Karur material reaches the international market through cutters and dealers in Coimbatore, Jaipur and Mumbai, and from there into the broader Asian and Western trade. Origin attribution at the laboratory level is generally not made for Karur chrysoberyl; the practical trade descriptors are "Indian alexandrite", "Indian cat's-eye chrysoberyl" or, for material of genuine quality and documentation, references to the Tamil Nadu source. Premium Sri Lankan and Brazilian material commands higher prices in the cat's-eye and alexandrite categories respectively, with Karur production occupying a useful commercial-quality middle band.

For the working trade Karur stands as a reminder that southern India remains a meaningful supplier of chrysoberyl and alexandrite alongside the better-known Sri Lankan, Russian, Brazilian, Tanzanian and Madagascan sources. The material is generally honestly identified at the cutter level but origin claims should be supported by knowledgeable supplier relationships rather than taken at face value, since trade chains pass through multiple hands between recovery and the international buyer.