Sapphire is the most precious and valuable blue gemstone. It is a very desirable gemstone due to its excellent color, hardness, durability, and luster. In the gem trade, Sapphire without any color prefix refers to the blue variety of the mineral Corundum.
It is the second hardest substance on earth after diamond, rating 9 on the Mohs scale of mineral hardness. Corundum itself is not a very rare mineral, but gem quality corundum is extremely rare. Most corundum is opaque to translucent and heavily included, suitable only for industrial use, including the production of abrasives used for sandpaper and machining of metal, plastics and wood. The name corundum comes from the Sanskrit word kuruvindam, meaning "ruby sapphire", while the name sapphire comes from the Persian word safir, derived from the Greek word for blue. In times of antiquity and the Middle Ages, the term sapphire actually referred to lapis lazuli, but in the early 19th century, the description and definition of sapphire was changed to the corundum variety we know today.
Sapphire is found in only a few locations in the world. The three most famous regions for blue sapphire are Kashmir, Burma and Sri Lanka. Sapphire has also been mined in Cambodia, Thailand, Vietnam and India. Today, Madagascar and Tanzania are considered to be two of the most important sapphire sources. Australia is also known for significant sapphire deposits, though most Australian sapphire is known to form rather dark in color. In the USA, there are small sapphire deposits found throughout Montana and North Carolina.
The finest quality blue sapphire, based on past auction prices, comes from Kashmir and Mogok, Burma. The most valuable color of Sapphire is a cornflower blue color, known as Kashmir Sapphire or Cornflower Blue Sapphire.The finest Kashmir and Burmese sapphires display superb color and clarity without any thermal (heat) treatment. Some Sri Lankan (Ceylonese) sapphires are also unheated, but nowadays, the majority of sapphires have been heated, diffused or fracture-filled to improve color and clarity, regardless of their origin.
The Kashmir mines, high up in the Himalayas, have produced spectacular world-renowned gems, but since the 1920s, virtually no new material has been found. The rare, fine blue sapphires of Pailin, Cambodia were also very highly regarded by gem traders throughout the world. Pailin sapphires ranged in color from light to deep blue, but they possessed a distinctive purity and intensity of color that was unlike any other sapphire sources.
Another extremely valuable Sapphire form is the very rare, orange-pink Padparadschah. An exotic type of sapphire, known as Color Changing Sapphire, displays a different color depending on its lighting. In natural light, Color Changing Sapphire is blue, but in artificial light, it is violet. This effect is the same phenomenon well-known in the gemstone . Yellow and pink Sapphire have recently become very popular, and are now often seen in jewelry
Almost all the sapphires from around the world are cut and processed in Chanthaburi, Thailand. Along with Kanchanaburi and Trat, Chanthaburi was once one of main sources for Thai sapphire. Sapphire mining in Chanthaburi is mostly finished now, though there are a few small private mining locations scattered throughout the province. There is also a large market for Thai star sapphires that exhibit distinctive golden six-rayed stars. The golden black star sapphire is found nowhere else in the world.
Nowadays, Chanthaburi, Thailand has become the main processing and trading center for almost all of the world's sapphires, rubies and other colored gemstones.