Sapphires are the gemstone for September. Sapphires, along with rubies, belong to the corundum family of gemstones and have a hardness on Mohs’ scale of 9, making them a very hard stone and ideal for use in jewellery. Sapphires come in many colours although the best known colour is blue. When referring to sapphires that are not blue, the correct description is a pink sapphire or a yellow sapphire, but it is understood that when a stone is described as being a sapphire, it is a blue stone.
The main colours of the sapphire family are blue, yellow, pink, colourless (or white), and black. There can also be orange, green and purple. One extremely rare colour sapphire is the padparadscha, which is a vibrant mixture of pink and orange. There is also a change colour sapphire. A rare stone is a star sapphire, showing asterism or rays like a star.
Typical inclusions in sapphires include ‘silk’ which are needle-like inclusions and colour zoning or banding. The ring below shows strong colour zoning.
Gem quality sapphires are found in a number of countries , including Australia, Sri Lanka, Thailand, USA, Myanmar (Burma), Thailand, India, Kashmir, Cambodia, Madagascar, Tanzania, and China.
It is important to be aware of two issues with sapphires – treatments and synthetic stones. Treatments to enhance and improve sapphires are common. Most sapphires for sale today will have been heat treated to remove inclusions and enhance the colour. This treatment should be disclosed to purchasers. Sapphires that are not heat treated and which have both pure colour and few inclusions are very expensive and will be accompanied by a certificate of quality.
Other treatments include surface diffusion in which a colour is baked or infused onto the surface. Such treatments are not stable and must be disclosed.
Synthetic sapphires were first created in 1902 by Auguste Verneuil in France. Many other processes for creating man-made or synthetic sapphires now exist. Synthetic sapphires possess the same chemical structures as natural sapphires but their value is much lower. Again, retailers should inform customers when stones are synthetic.