Sri Lankan sapphire (Ratnapura)

Ratnapura takes its name from two Sanskrit words, ratna, gemstone, and pura, town: the city of gems. It sits on the Kalu Ganga, the Black River, in the wet south-west of Sri Lanka about 101 km from Colombo, and it is the traditional heart of the island's gem trade.

The stones come out of the gravel. Sri Lanka's gems grew in the high-grade metamorphic rocks of the Highland Complex, many of them between 539 and 608 million years ago, a time of peak metamorphism when the island was part of Gondwana. Weathering freed the crystals and water concentrated them in gravel beds the miners call illam, which GIA's field gemologists count among the richest in the world. Sapphire is the prize, but the same gravels give up ruby, spinel, garnet, topaz, tourmaline and cat's-eye chrysoberyl.

Mining here is small-scale by design. A standard pit is a vertical shaft two metres by four, most of them 5 to 25 metres deep, sunk among the paddy fields under a little V-shaped roof. Miners toss the gravel up in baskets, and every pit is a partnership: the landowner, the holder of the mining rights, whoever supplies the water pump, and the miners all take a share of what the stones fetch. Of more than 6,500 licences issued in 2013, over 6,000 went to traditional pits and only about ten to mechanised mines. More than two million pits are thought to have been dug in the last 50 years, yet hardly any lie open, because the National Gem and Jewellery Authority holds a cash deposit from every licensee and spends it on restoring the ground if the owner does not. The work pays well enough that many farmers around the town have traded rice for gem mining.

Every day traders from the suburbs and nearby towns crowd into the centre to buy and sell, at three main markets, Abagahamula, the Clock Tower and Demuwamawatha. Thai buyers are the largest group of foreign traders, heat treaters known as burners work at every major market, and since the great sapphire strike at Ilakaka in Madagascar many Ratnapura merchants fly there to buy rough.

The island's most famous sapphire lives in New York. The Star of India, a 563.35-carat greyish-blue star sapphire from Sri Lanka, almost flawless and starred on both sides, was acquired for J. P. Morgan's collection for the Paris Exposition of 1900 and given to the American Museum of Natural History. In October 1964 thieves including Jack Murphy, "Murph the Surf," climbed in through a bathroom window and took it; the only alarm guarding it had a dead battery. It turned up in January 1965 in a bus station locker in Miami.