Spinels: A Misunderstood Gemstone

Posted: July 13, 2012 - 14:30 , by Katherine Dunnell
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Rubies, emeralds and diamonds are words you immediately associate with gemstones, but mention spinel and people give you a questioning look.  Gem spinels have been mined and used in jewellery for hundreds of years and are a very attractive and popular gem in high-end jewellery, but rarely seen in jewellery stores.  Why is this?  The answer from many jewellery retailers is that people only buy what they understand, and outside of North America, the market is less diamond centric and coloured stones like spinel do sell. Spinels come in an attractive array of colours, and for some time, were mis-identified as corundum (sapphire) as they are found together in the same deposit and gem gravels. One of the most historic mix ups is in the Imperial State Crown, where the 170 carats centre “ruby” was a misidentified red spinel or also known as “balas ruby”.

Spinel is a magnesium aluminium oxide mineral, and its counterpart corundum (the red variety is called ruby while the other colours are known as sapphire) is aluminum oxide mineral.  In geologic environments, spinel forms first and when the conditions are right corundum starts to form.  This is one of the chief reasons why there is more spinel crystallizing than corundum and why they are both found together.  Spinel, like it’s counterpartcorundum, can be found in the array of colours, from colourless to vivid blues, pinks and the most sought after, red.  In terms of their characteristic properties, spinel has a hardness of 8 on the Mohs hardness scale, while sapphire is a hardness of 9. Spinel is less dense than sapphire, therefore giving you a bigger stone for the same carat weight at a cheaper price. Spinels are usually derived in metamorphic or to a lesser extent, primary igneous environment. The bulk of the gem quality spinels mined today are found in metamorphic environments, such as areas in Sri Lanka, Tanzania, Madagascar, Myanmar, Afghanistan, and Kenya.  Some chondritic meteorites often contain spinel in the calcium-aluminum rich inclusions (CAI’s) so spinel is an extra-terrestrial mineral as well!

The ROM is fortunate to have a fabulous array of spinels on display and the most significant being this lovely lavender pear shaped 61.45 carats spinel from Myanmar (formerly Burma).  Dr. Vic Meen, curator, traveled extensively in the gem regions of the world building the gem collection at the ROM.  This was one of his many purchases while he was inMyanmar in June of 1960. Personally, my love of spinel is strong and I have always had an affinity for the underdog.  I am drawn to the complex colour in spinel that sapphires lack, and when it was time to purchase my engagement ring, spinel was gemstone of choice.  I have never regretted my decision.

 

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