Natural spinel continues to be one of the most undervalued of the fine gemstones. The reasons are largely historical. Because spinel is found in the same locations as corundum, specimens of spinel were often misidentified as ruby or sapphire. The most famous example is the Black Prince's Ruby, a huge uncut spinel mounted in the front of the Imperial State Crown of the United Kingdom. This remarkable gem, weighing approximately 170 carats, has been in the possession of the British royal family since the 14th century and until recently was believed to be a ruby.
Spinel was recognized as a distinct gem type only in 1783. While it is nearly as hard as sapphire or ruby (rating 8 on the Mohs scale compared to 9 for corundum) and has a similar refractive index, spinel is one of the very few gemstones that is singly refractive. That makes it very easy to distinguish from corundum using simple instruments.
Another historical factor contributed to spinel's valuation in the mind of consumers. When Auguste Verneuil perfected the flame fusion process for creating synthetic corundum in 1902, the same method was applied to creating synthetic spinel. Lab-created spinel is very commonly used in cheap birthstone jewelry and school rings, since it can be created in any color.
Fortunately the synthetic spinel has a different chemical composition from natural spinel, with more aluminum than magnesium. Corresponding to the chemical difference, synthetic spinel has a different refractive index and specific gravity as well, making it very difficult for the synthetic to be sold as natural.
Many gem dealers and gemologists believe spinel is undervalued is because of its outstanding gemstone characteristics and its rarity. Fine spinel compares favorably with ruby and sapphire for brilliance, luster and fire, and it is a very durable gem with excellent hardness and indistinct cleavage. It also occurs in a wide range of colors, ranging from red and pink, to violet, blue, green, orange, green and silver.
But what makes natural spinel rather special in today's gemstone market is that it is never heated or treated by any other method. Thus far there is no known treatment that can improve the color or clarity of natural spinel. By contrast, nearly all the sapphire and ruby in the market has been enhanced by heat treatment. It is surprising then that untreated spinel still sells for less than 50% the price of heated sapphire or ruby. It is a situation that is likely to change as the virtues of spinel become better recognized in the market.
- First Published: December-17-2008
- Last Updated: March-09-2011
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