All About Sapphires

Sapphire Facts

The name sapphire may derive from the Greek Sanskrit 'sanipriya', meaning "dear to the planet Saturn.". It is a single-crystal form of aluminium oxide and a mineral known as corundum. It is found either naturally as gemstones or is manufactured in large crystal boules for a variety of applications.

Sapphire actually includes any gemstone quality varieties of the mineral corundum other than the red ruby. Sapphire is usually blue but can also be purple, yellow, orange, pink or green. Sapphires are just below diamonds on mohs hardness scale and rate a a hardness of 9, and do not cleave which makes them perfect for faceted gemstones.

Blue sapphires come in a wide range of shades of blue. Titanium and iron inclusions within the aluminium oxide result in various shades of blue. Some stones are not well saturated and show tones of gray. To give a better blue 90% of all sapphires are heated treated to a temperature of 3000 °C. The way to tell if the sapphire has been heat treated is to check the the rutile needles within the stone under magnification. If the needles are unbroken, then the stone has not been heated. If the silk is not visible then the stone was heated adequately. If the silk is partially broken then a process known as low tube heat was used. Low tube heat is the process where the rough stone is heated to 1000 °C for 10 to 20 minutes. This takes out any gray in the stone and improves color saturation.

Fancy sapphires are any sapphire other than blue or red. Purple sapphires are lower in price than blue ones. These stones contain the trace element vanadium and come in a wide variety of shades. Yellow and green sapphires have traces of iron which gives them their color. Pink sapphires have trace element of chromium and the deeper the color pink the higher the value as long as the color is going toward red of rubies. Color shift sapphires are blue in outdoor light and purple in indoor light. Some stones shift color well and others only partially, in that some stones go from blue to blue purple. White sapphires usually come out of the ground as light gray or brown and are then heated to make them clear. However in very rare circumstances they will be found in a clear state.

Sapphires are mined from alluvial deposits or from primary underground workings. Historically, most sapphires have been mined in Sri Lanka, Madagascar and Myanmar. Australia, currently leads the world in sapphire production from basalt derived placer deposits in Queensland and New South Wales. Pakistan, Afghanistan, India and Kenya also produce sapphires. The US state of Montana has produced sapphires from the Yogo Gultch deposit near Helena.

Synthetic sapphire crystals can be grown in cylindrical crystal ingots of large size, up to many inches in diameter. As well as gemstone applications there are many other uses.

The first ever laser produced was based on the ruby chromium impurity in sapphire. While this laser has few commercial applications, the Ti-sapphire laser is popular due to the relatively rare ability to tune the laser wavelength in the red-to-near infrared region of the electromagnetic spectrum. It can also be easily modelocked. In these lasers, a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.

Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Such slices are used as watch faces in high quality watches, as the material's exceptional hardness makes the face almost impossible to scratch. Since sapphire ranks a 9 on the Mohs Scale, owners of such watches should still be careful to avoid exposure to diamond jewelry, and should avoid striking their watches against artificial stone and simulated stone surfaces. Such surfaces often contain materials including silicon carbide, which, like diamond, are harder than sapphire and thus capable of causing scratches (Scheel 2003).

Wafers of single crystal sapphire are also used in the semiconductor industry as a substrate for the growth of gallium nitride based blue and green light-emitting diodes.

A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism (gemmology). Star sapphires contain intersecting needle-like inclusions (often the mineral rutile) that cause the appearance of a six rayed 'star' shaped pattern when viewed with a single overhead light source. Twelve ray stars are also found, but are less common.

The value of a Star Sapphire depends not only on the carat weight of the stone but also the body color, visibility, and intensity of the star. Some sapphires are heat-treated or otherwise enhanced to improve their appearance and color, though some people object to such practices and prefer natural untreated stones. Treated stones tend to be darker than untreated stones and the treatment process causes changes to the internal structure that are generally easily detected.