|The Secret of Spinel
Natural spinel is a gemstone that is not well known in the commercial jewelry world, but one which has become a great favorite with gem dealers and gem collectors. One might even say that spinel is for gemstone connoisseurs only. What has gem experts so excited about this gemstone?
Spinel is a magnesium aluminate, colored by chromium and iron. It is quite hard (8 on the Mohs scale), and it forms as a cubic crystal like a diamond. Spinel occurs in octahedral crystals, and has a complete absence of cleavage (unlike diamond). Due to spinel's excellent dispersion, gem spinels can possess vivid fire, and the intensity of spinel color is partially due to the fact that spinel is singly refractive. Most gemstones are doubly refractive; in fact only diamond, spinel and garnet are singly refractive.
Spinel is usually formed as a contract metamorphic mineral in limestone. It is discovered as rolled pebbles in sand and gravel pits. Spinel today is mined primarily in Burma, Sri Lanka, Tanzania and Tadjikistan, often along side corundum (ruby and sapphire). Large stones are very rare; a ten carat sized Burmese spinel is practically nonexistent. Most of the Burmese spinel is under 2 carats, but we do see some larger spinel from Tanzania.
The most sought after colors by collectors are red, hot pink, and flame orange. Any spinel over two carats is rare. The most valuable spinel is red/red or red/orange. But one of the attractions of spinel is that it comes in a wide range of gorgeous colors. For red spinel, the finest colors tend to be similar to ruby, i.e. a rich, intense red similar to that of a red traffic signal. However, spinel tends to be a bit more of a brick red than ruby (which is slightly more purplish). Like all gems, the most coveted are those whose color is intense, while being neither too light nor too dark. The value of red spinel tends to decline as the color diminishes into either light pinks or 'garnety' reds. Spinel is also found in a deep blue known as cobalt blue, and in pastel hues of pink, violet, blue-green, silver, rose, bronze and orange. There is also a black spinel variety found in Thailand and Australia.
So what is the great secret of spinel? The answer is that spinel is in many respects the equal of ruby and sapphire. Though ruby is slightly harder (9 vs 8 for spinel), spinel contains fewer inclusions than ruby, and spinel has greater fire and brilliance. Spinel is never heated or treated in any way; indeed, there is no known treatment for improving the color or clarity of spinel. Virtually every affordable ruby these days is treated in some way. Also, since spinel is singly refractive and ruby is doubly refractive, the primary color in red spinel appears purer and more intense than the reds seen in many rubies. But spinel is typically 20-50%% the price of ruby. That makes spinel a tremendous value in a market where prices for fine gems are rising every year.
Why then isn't spinel better known and more highly valued? The simple answer is that supply is very limited, and the jewelry industry doesn't market what it can't get. So spinel continues to be mainly a collector's stone. Here at GemSelect we are lucky to be located close to the source of the finest spinel in Burma, and our home of Chanthaburi is a major cutting and trading center for Tanzanian spinel. So while spinel supply is indeed limited, we have better access to the supply than most gem dealers in the world. Spinel is still a secret to many people, but it's a secret we like to share with our customers.
- First Published: October-17-2007
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