A to Z of Gemstones: S: Sapphire


Gemstone family: Corundum

Crystal System: Hexagonal

Moh's scale of hardness: 9

Lustre: Vitreous to sub-adamantine

Birthstone: September

About: The name “sapphire” derives from the word “sappheiros” in ancient Greek and is a variety of the corundum species.  “Sapphire” always refers to stones that vary from violetish blue to slightly greenish blue and it’s primarily the presence of iron and titanium trace elements that produce these beautiful blues. The most valuable colour of sapphire is what is known as the “cornflower blue” or “Kashmir” which is a strong pure blue to violetish blue and sometimes has a velvety look.  Any other colour, besides red which would make it a ruby, is considered a fancy sapphire such as yellow sapphire, green sapphire and pink sapphire.  Within the fancy sapphire range the rarest and most prized colour is the padparadscha which means “lotus flower” in Sinhalese. The stone is found in Sri Lanka and has a vivid orangey pink to pinkish orange stiking colour which is caused by iron and chromium trace elements or by colour centres.   One interesting thing that you might find in sapphires is an inclusion also knows as “silk” consisting of fine rutile needles that give a velvety-milky look to the stone.  Some sapphires can display what is called in gemmological terms, a “phenomenon”. Two of the most important types of phenomenal sapphire are colour-change sapphires and star sapphires. The former change colour when seen under a daylight equivalent light source and under incandescent lighting and the latter are cabochon-cut stones that display a whitish star created by fine intersecting needle inclusions.

Origin: Mines that have yielded the finest sapphires in colour and clarity are located in Kashmir, Myanmar and Sri Lanka. Nowadays the main sources of sapphires are: Thailand, Cambodia, Australia, Madagascar and Montana in the U.S.A.

Use in jewellery: Sapphire’s lustre is vitreous to sub-adamantine; it rates 9 on the Mohs scale and therefore it is ideal for jewellery that is worn frequently.  Depending on the transparency of the stone which can be anything between transparent and opaque sapphires are cut into faceted stones, cabochons, beads and carvings.

Treatments, synthetics and imitations: Sapphires are often treated to enhance their colour or improve their clarity; some of the most common treatments are: heat (with or without the use of chemicals), lattice-diffusion and beryllium-diffusion.  Synthetic sapphires have the same chemical properties to the natural sapphires but their value is significantly lower so they should always be disclosed as synthetic.  Some of the materials that are mostly used to imitate sapphires are: glass, garnet-and-glass doublet, synthetic spinel triplet and sapphire and synthetic sapphire doublet.

Famous examples: The largest faceted sapphire in the world is the “Blue Giant of the Orient” which has an intense medium blue colour and is cut into a cushion shape. It weighs a huge 486.52cts.