Natural spinel continues to be one of the most undervalued of the fine gemstones. The reasons are largely historical. Since 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 with the use of simple instruments.
Another historical factor contributed to spinel's value in the minds of consumers. When Auguste Verneuil perfected the flame fusion process for creating synthetic corundum in 1902, the same method was applied to the creation of synthetic spinel. Such lab-created spinel is very commonly used in cheap birthstone jewelry and school rings, since it can be created in any color.
Fortunately, synthetic spinel has a different chemical composition from natural spinel, with more aluminum than magnesium. Due to this chemical contrast, synthetic spinel also has a different refractive index and specific gravity, making it very difficult for the synthetic variety to be sold as natural material.
Spinel is quite rare and many gem dealers and gemologists believe that it has outstanding gemstone characteristics. This leads to the widespread belief that spinel is undervalued. 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, orange, green and silver.
However, what makes natural spinel rather special on today's gemstone market is that it is never heated or treated. To date, there is no known treatment that can improve the color or clarity of natural spinel. Conversely, a great deal of sapphire and ruby on the market has been enhanced by heat treatment. This makes it surprising that untreated spinel still sells for less than 50% of the price of heated sapphire or ruby. It is a situation that is likely to change as the virtues of spinel become better recognized.
- First Published: December-17-2008
- Last Updated: October-03-2014
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