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August 2, 2017
Fourteen months ago, the American Gem Trade Association (AGTA) and Jewelers of America (JA) announced that spinel — the great imposter — would be joining peridot as an official birthstone for the month of August. It was only the third time in the past 105 years that the modern birthstone list had been amended.
The industry associations noted at the time that they were responding to a strong call from gem enthusiasts to expand the list of official birthstones. The spinel was designated for August because of its historical significance and its rich, red color.
Spinel has been called “the great impostor of gemstone history” because some of the most famous “rubies” seen in crown jewels around the world are actually spinels. According to the Smithsonian, it wasn't until 1783 that spinel was recognized as a mineral distinct from corundum (ruby and sapphire). Ruby is composed of aluminum oxide, while spinel is made of magnesium aluminum oxide. Both get their reddish color from impurities of chromium in their chemical structure.
For centuries, royal jewelry "experts" could not tell the difference between a ruby and a spinel.
For instance, the 398-carat ruby-red gem that tops the Imperial Crown of Russia commissioned by Catherine the Great in 1763 was thought to be a ruby, but turned out to be a spinel. The 361-carat Timur Ruby, which was presented by the East India Company to Queen Victoria as a gift in 1851, was also later identified as a spinel. And the 170-carat Black Prince Ruby, which is prominently displayed on the Imperial State Crown of England, was, in fact, an uncut spinel.
While spinel is best known for its ability to imitate the color of ruby, the gem comes in a variety of vibrant colors, including soft pastel shades of pink and purple, fiery oranges, and cool hues ranging from powdery gray to intense blue. It is a durable gem with a hardness of 8.0 on the Mohs scale. By comparison, diamond rates a 10 and ruby rates a 9.
Shown in the image, above, are three spinels from the National Gem and Mineral Collection at the Smithsonian’s National Museum of Natural History in Washington, D.C. The first and third gem were sourced in Sri Lanka and weigh 22.2 and 29.7 carats, respectively. The spinel in the center is from Myanmar and weighs 36.1 carats.
The bracelet shown here contains 98 natural spinel crystals set in a double row in yellow gold. The stones were sourced in the Mogok region of Myanmar and the piece is currently part of the National Gem and Mineral Collection.
Myanmar is known to produce some of the most beautiful spinels — especially the pink, red and orange-red varieties. Spinels are also mined in Afghanistan, Brazil, Cambodia, Kenya, Russia, Sri Lanka, Tanzania, Thailand and Vietnam.
Credits: Gem photo by D. Penland/Smithsonian. Bracelet photo by Chip Clark/Smithsonian.