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Star Sapphires – Something Different Again.

by Gary Hocking

Star sapphires are different to your normal sapphire because they are not faceted.  Facets are the flat planes that you see in diamonds and sapphires, rubies and emeralds as well as many other stones.  But star sapphires are cut into cabochons. A cabochon is the rounded or domed smooth cut.  It comes from an old French word with means hat.

The star effect comes from an inclusion.  An inclusion is what might be termed a fault in a gemstone. They might be cracks, fissures, pieces of foreign bodies or growths inside the stone of some kind.  The best known inclusion would be a fly trapped inside a piece of amber.

Some sapphires and even rubies have a certain kind of inclusion which are like tiny needles known as rutile or silk.  When the stone is cut into a cabochon  we see a six-rayed, or sometimes a twelve pointed white star.  When we move the stone around the star moves as well across the face of the stone an effect known as asterism.

It is a good way to tell if the stone has been heat treated because if the rays are unbroken then it means that no heat treatment has taken place.  99% of all sapphires are heat treated to enhance their colour.  They are heated to a temperature of 3000 degrees C.

The value of a star sapphire or star ruby depends on the intensity of the body colour and the sharpness of the star.  The legs should be straight and should be of equal thickness.

Star sapphires are rare but mainly because the stones are heat treated after mining and then cut with facets so the stars are never seen again.  Stars are also found in other stones.

In ancient times star sapphires were particularly highly regarded as the star supposedly would assist travelers by being a guiding star.

Today they are rare and well prized and they make wonderful jewellery.  A star sapphire ring is particularly interesting and is a good conversation piece as people are always willing to have a look at something different.