Star Sapphire Gemstone

Star Sapphire Gemstone
[For Information and Educational purposes only]
by Alice Koh

Sapphire comes from the Greek SAPPHEIROS which means blue stone. Don't get confused with the Latin word for blue stone which is lapis lazuli. In ancient times lapis lazuli and blue sapphire referred to a specific colour and not a mineral nor material.

Sapphire and ruby are one and the same, sharing not only their chemical composition but both are equally famous, valuable and extremely rare (rarer than diamonds). They belong to the same corundum family but rubies come in different shades of red whereas sapphires are well known for their blue colour although they can also be found in yellow, green, orange and purple; there are also colourless and black sapphires.

Sapphire refers to the blue coloured stone. All other colours are known as fancy sapphires but this term does not apply to the colourless, black and the blue varieties.

The colours of sapphire are caused by mineral impurities within the stone. A trace presence of chromium, iron or titanium minerals create the colours in both sapphire and ruby.

Star sapphire is of an aluminum oxide chemical composition. It forms in a (trigonal) doubly pointy, barrel-shaped, hexagonal pyramids, tabloid-shaped crystal structure. It has a hardness of 9 on the Mohs scale with a refractive index ranging from 1.762 to 1.778. It has no distinct cleavage. Star sapphire is typically opaque. Some finer specimens may exhibit slight translucency. It has a glass-like, silky luster.

Star sapphire is made up of unusual small needle-like inclusions of rutile that make possible the rare phenomenon of the star effect in a sapphire gemstone. This effect is called asterism. When viewing star sapphire, a six-rayed star will appear to float across the surface of the stone. This is best viewed under a direct light source or when you tilt and rotate the gemstone from different angles

Usually a star sapphire will display a white six-rayed star but the star sappire from Thailand is famous for its golden coloured six-rayed star.

Star gemstones that look similar to star sapphire include star garnet and star diopside.

Star sapphire comes in various blue tones, pink, yellow, orange, green, lavender, gray, black and white. The colouring agents are iron and titanium in blue sapphire and vanadium in violet to purple star sapphire. Iron produces the yellow and greenish hues and chromium produces fine pink to red tones. Iron and vanadium result in golden to orange tones.

Star sapphires are usually cut en cabochon with very high domes. The best cabochons are translucent, with even roundness to the shape.

Star sapphire is generally heat treated to improve the clarity and colour of the gemstone. In order to create a more visible star effect, the sapphire gemstone is heated with titanium.

Specific varietal trade names of star sapphire are based on its colour, origin and unique traits such as colour change sapphire, Ceylon sapphire or Padparadscha sapphire.

Sapphire is the birthstone for those born in September under the zodiac sign of Taurus.

Star sapphires were regarded in ancient times as powerful amulets for protection for travellers and seekers. These amulets were considered so powerful that they were passed from one generation to the next.

Some black sappires are found in large sizes but usually star sapphires occur in small sizes. The most popular star sapphires are the blue and black coloured gemstones. The most sought after colour is the vivid blue.

Star sapphire important sources come from Australia, Myanmar (Burma), Sri Lanka and Thailand. Other sources include, Brazil, Cambodia, China, Kenya, Madagascar, Malawi, Nigeria, Pakistan, Rwanda, Tanzania, United States (Montana), Vietnam and Zimbabwe.