Sapphire

Corundum needs a silicon-free growth environment, which makes natural corundum relatively uncommon. Kashmir, Myanmar (Mogok) and Sri Lanka are historically important sources; Kashmir sapphires were discovered around 1881 and mined intensively from 1882 to 1887. Sri Lanka has supplied sapphire from alluvial gravels for more than 2,000 years. Significant quantities also come from Australia, Thailand (Chanthaburi, also a major cutting and treatment centre), Cambodia, Madagascar, Tanzania and the United States (Montana); discoveries in East Africa and Madagascar in the 1990s greatly increased the supply of fancy colours.

Sapphire shares its mineral and properties with ruby; only red corundum is called ruby. Sapphire often contains fine intersecting rutile needles called "silk", and oriented needle-like inclusions can produce a six-rayed star in cabochons; some stones change colour, usually from blue in daylight to purple under incandescent light. Heat treatment is common and permanent and is well accepted in the trade; milky white Sri Lankan "geuda" can be heated to a rich blue. Less common treatments include lattice diffusion (whose colour may be so shallow that chipping or recutting removes it), fracture filling and dyeing. Synthetic sapphire is also made, so ask about treatment and use a laboratory report to confirm natural origin.

With a Mohs hardness of 9, excellent toughness and no cleavage, sapphire is a good choice for rings and other jewellery worn daily. Warm, soapy water is always safe. Ultrasonic and steam cleaners are usually safe for untreated, heat-treated and lattice diffusion–treated stones; fracture-filled or dyed sapphires should be cleaned only with a damp cloth and can be damaged even by mild acids such as lemon juice.

The name comes from the Greek sappheiros, which probably referred to lapis lazuli. Sapphire has decorated the robes of royalty and clergy for centuries, and colourless sapphires were once popular diamond imitations. Famous stones include the 62.02-carat Rockefeller Sapphire from Myanmar and the 12-carat blue sapphire in the engagement ring Prince Charles gave Lady Diana Spencer in 1981, later worn by Kate Middleton. The orangy pink colour called padparadscha takes its name from the Sinhalese word for lotus flower; at first only Sri Lankan stones carried the name.

Traditionally, sapphire symbolizes nobility, truth, sincerity and faithfulness. As GIA recounts, rulers in ancient Greece and Rome believed blue sapphires protected their owners from envy and harm; medieval clergy wore them to symbolize Heaven, and ordinary people thought they attracted heavenly blessings. Ancient Persians believed the earth rested on a giant sapphire that made the sky blue, and medieval Europeans believed sapphire cured plague boils and eye diseases and was an antidote to poison. These are traditional beliefs, not verified effects.

Sapphire is the traditional birthstone for September and the gem for the 5th and 45th wedding anniversaries.