Sapphires from Thailand
As early as the 15th century, visitors to Thailand forwarded glowing reports of the fabulous rubies and sapphires that could be found there. In 1687, the French envoy to Siam reported that the country was “abounding in mines of rubies and sapphires.” He also noted that the local Thai farmers used these gemstones as amulets.In the environs of Chanthaburi, a famous mining area in the southeastern corner of the country, sapphires were discovered as villagers planted their crops. Before these farmers had any inkling of their value, the gemstones were quickly purchased for a fraction of their true worth.
The Chanthaburi area has produced large quantities of corundum from alluvial deposits of weathered alkali basalts. Although rubies have traditionally outnumbered the sapphires found in this area, blue, blue-green, and yellow sapphires, as well as black star sapphires, can be found. Some of the yellows of this region have the prized golden-yellow, “Mekong Whisky” color desired by consumers. This area was heavily mined during the 19th and early 20th century, until another, more lucrative source was found at Kanchanaburi.
The Kanchanaburi mines, almost due west of Bangkok, were discovered in 1918. The area became the world’s leading source of commercial rough during the 1980s and 1990s when a mining boom took place. The Kanchanaburi mines yield blue, yellow, pink, and star sapphires, although production has now declined significantly.
Characteristics of Thai sapphires include uneven color zoning and a slight milkiness. Because Thai sapphires are often dark, they are frequently heat-treated. Bangkok and Chantaburi have become major sapphire cutting, treating, and marketing centers drawing an international clientele. It is estimated that about 70 percent of the world’s sapphires pass through Thailand before reaching the consumer.
Since 1919, when the Siam Mining Act was passed, gem extraction has been limited to Thai nationals. Mechanized mining was banned for several years because farmers protested that mining was destroying the topsoil, but this situation changed in 1987. Mining continues at Chanthaburi and Kanchanaburi, but production is at a low point. Some mechanized mining is also taking place in northern Thailand near Phrae, but only limited production has been reported.