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Sapphire

A clear hard variety of corundum used as a gemstone that is usually blue but may be any color except red.

The name given to all gem varieties of the mineral corundum, except those that have medium to dark tones of red that characterize ruby. Although the name sapphire is most commonly associated with the blue variety, there are many other colors of gem corundum to which sapphire is applied correctly; these include yellow, brown, green, pink, orange, purple, colorless, and black. Sapphire has a hardness of 9, a specific gravity near 4.00, and refractive indices of 1.76–1.77. Asterism, the star effect, is the result of reflections from tiny, lustrous, needlelike inclusions of the mineral rutile, plus a domed form of cutting.

See also: Corundum; Ruby; Rutile.

Material Notes:
Sapphire is grown by several methods: Boule form (Czochralski), in plate form, or as tubes, rods and plates. Boules are grown up to 8" diameter and 6" long. Plates can be formed up to 12" square and 1" thick. Rods and tubes can be grown up to 72" long.

Sapphire is characterized by its high hardness (next to diamond on the Mohs scale), chemical and thermal stability, high application temperature, and transparency in the IR range. It is widely used as windows for instruments, high temperature parts, and wear resistance.

Also used for deposition of III-V nitrides for LEDs, Lasers, etc. Standard orientation: <0001>; GaN Lattice Mismatch 14%.

The gem’s inclusions reflect light that yields a faint sheen referred to as “silk.” The most transparent, colorless variety of sapphires are known as “Leucosapphire.” Some have streaks of pale color inside, some have that slightly silky sheen and in strong light, their color intensifies. Sapphires are usually given round or oval cuts but rectangular or square cuts are also possible.

To keep your gems sparkling, clean them when dust and fingerprints have dimmed their brilliance. The best way to clean your gemstone jewelry is in a bowl of water with a few drops of ordinary dish detergent. Using an old toothbrush or other soft brush, scrub gently behind the gemstone where dust and soap can collect. Dry your jewelry thoroughly with a soft cloth, and use ‘Q tips’ to get into the more difficult places.

Although Sapphires are well known for their durability you should remember that hardness and susceptibility to breakage are not related. Although a Sapphire scores 9 out of 10 on the Moh’s scale, second only to diamond, most are included. Some Sapphires are heavily included, in the case of Star Sapphire, making the gem fragile and susceptible to cracking or chipping if hit.

However, if you use your common sense this can be avoided. Remove jewelry before doing heavy work. Take care of your Sapphire by treating it gently and by keeping your gems and jewelry clean. Lightly included gemstones usually go safely into ultrasonic cleaners.

Because of their hardness, Sapphires can be cleaned in almost any way. Warm, soapy water is best, though you might also try ultrasonic cleaners and steamers. You can also try using water with a touch of ammonia in it. If you have a fracture in your sapphire or own a star sapphire, do not use mechanical cleaning methods as a sapphire can shatter with one single blow, if hit sharply. This may be especially risky if the stone has inclusions, which weaken the crystal structure. As with most valuable stones, avoid doing heavy work or coming into contact with chemicals while wearing your stone, as they can damage your settings.

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