The Secret of Spinel
Red Spinel Gems
Natural spinel is a gemstone that is not well-known in the commercial jewelry world but has become a great favorite with gem dealers and gem collectors. One might even say that spinel is for gemstone connoisseurs only. What has got gem experts so excited about this gemstone?
Spinel is composed of magnesium aluminate, and colored by chromium and iron. It is quite hard (8 on the Mohs scale), and it forms as cubic crystals like diamond. Spinel occurs in octahedral crystals, and has a complete absence of cleavage (unlike diamond). Due to spinel's excellent dispersion, spinel gemtones can possess vivid fire. The intensity of color is partly due to the fact that spinel is singly refractive. Most gemstones are doubly refractive. The best-known singly refractive gems are diamond, spinel and garnet.
Spinel forms as a contact metamorphic mineral in limestone. It is discovered as rolled pebbles in sand and gravel pits. Nowadays, spinel is mined primarily in Burma, Sri Lanka, Tanzania and Tajikistan, often alongside corundum (ruby and sapphire). Large stones are very rare; ten carat sized Burmese spinel gems are practically nonexistent. Most of the Burmese spinel is under 2 carats, but we do see some larger spinel gemstones from Tanzania.
The most sought-after colors of spinel are red, hot-pink, and flame-orange. Any spinel gem weighing over two carats is rare. The most valuable spinel is red or red-orange. 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 slightly more brick-red than ruby-red. Like all gems, the most coveted are those which display an intense hue, while being neither too light nor too dark. The value of red spinel tends to decline as the color diminishes into either light-pink or brownish-red. Spinel is also found in a deep-blue shade 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 on the Mohs scale), spinel contains fewer inclusions than ruby, and spinel has greater fire and brilliance. Spinel is never heated nor treated in any way; indeed, there is no known treatment for improving the color or clarity of spinel. Conversely, virtually every affordable ruby is treated in some way these days. Also, since spinel is singly refractive and ruby is doubly refractive, the primary color in red spinel appears purer and more intense than the red seen in many rubies. Yet, spinel is typically purchased for 20-50% the price of ruby. That makes spinel tremendous value on 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. Although spinel supply is limited, we have better access to the supply than most gem dealers. Therefore, spinel is still a secret, but it's a secret we like to share with our customers.
- First Published: October-17-2007
- Last Updated: January-24-2019
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