Sapphire is the gem variety of the mineral corundum. Although the term "sapphire" refers to the blue variety of corundum, sapphires occur naturally in colours as diverse as pink, orange, yellow and green. These are referred to as pink sapphires, orange sapphires and so forth. The exception is red corundum, known as ruby and this is discussed further in the ruby buying guide. Sapphires are mined in a number of countries, including Burma, Sri Lanka, Thailand and Madagascar. Compositional impurities determine the colour of a sapphire and traditional blue sapphires are a result of the presence of iron and titanium during crystal growth. Sapphire has a hardness of 9 (second only to diamond) and is thus perfect for use in rings, bracelets, pendants and earrings.
A well-cut sapphire will appear more vivid in colour and saturation when compared to a poorly cut sapphire. Cut affects both the depth of colour seen in the stone and the liveliness projected by the stone. Oval and cushion cut sapphires are the most common sapphire shapes, but heart, emerald, square, marquise and pear cuts are also seen. Round cut sapphires command higher prices than fancy shapes, due to a higher carat weight loss during faceting and polishing. Cabochon (dome-shaped) cuts are commonly applied to sapphires whose clarity is not ideal for polishing. Cabochon cuts are used to develop and display asterism in star sapphires.
The blue colour and the saturation of the colour are the primary factors determining the value of sapphires and an ideal sapphire displays an intense, rich blue. Saturation refers to the brightness or vividness of the colour and pure, vivid colours are more desirable than dull, muddy colours.
Ideally, a sapphire should be inclusion-free to allow the free transmission of light through the gemstone. In reality, sapphires often contain a number of inclusions and these are more easily observed in light coloured sapphires. Consumers should look for sapphires that show no inclusions visible to the naked eye.
The majority of sapphires sold today have been subjected to heat treatment processes. Subjecting cloudy and poor quality sapphires to high temperatures improves the quality and intensifies the colour of these sapphires. The results of these heating processes are permanent and a treated sapphire will not deteriorate in colour or clarity over time. Such enhancement of sapphires has ensured that today, sapphires are more accessible and affordable than before. It has been estimated that only 1% of sapphires sold today have not been heat treated and these command prices far in excess of those paid for treated sapphires.