By Cynthia Unninayar
Throughout its history, spinel has been one of the world’s most under-appreciated gemstones. Today, however, a quick tour around the world’s major gem and jewellery shows that spinel, in its myriad colours, is not only highly regarded, but it is the hottest gemstone of the year.
Spinel is a species of minerals made of magnesium and aluminium oxide, with the formula MgAl2O4 that forms in the cubic crystal system. It has a hardness of 8 on the Mohs scale and is heat-resistant. The name “spinel” may be derived from the Latin “spina” meaning “thorn”, due perhaps to the points of its octahedral structure in the gem’s rough form.
It is an “allochromatic” gemstone, meaning that it gets its colour from light absorbing “impurities”, i.e. trace elements that are not essential parts of spinel’s atomic structure, but that give the gem its colour. The most common “chromophores” found in spinel are cobalt, iron, chromium and vanadium. While the colour story is complex, fundamentally, the colours are created when one or a combination of these metals replaces the colourless magnesiumions in spinel’s chemical formula.
In its pure state—i.e. with no impurities—spinel is colourless, but this type is very rare in Nature. In general, its colours range from very light pastels to strong vibrant tones, in hues of pink, red, orangey-red, lavender, purple, blue, black and, rarely, green and yellow. Grey and blue spinels are the result of iron impurities, although the very saturated “cobalt blue” colour comes from the presence of cobalt in the crystal lattice. Chromium creates the pink and red tones, while different ratios of these trace metals results in the various tones of purple and lavender. Vanadium is thought to be responsible for the rare yellow and orangey tones. Today’s hottest colours in spinel are intense pink and red along with the electric “cobalt blue”.
Throughout most of its history, spinel was prized for its deep red colour, which resembles ruby. In ancient times, before mineralogy became a science, gems were categorized by their colour rather than their mineralogical or chemical properties. As a result, spinels were thought to be rubies. The confusion between the two gems lasted for centuries, until 1783 when spinel was chemically differentiated from ruby. Thus, some of the most famous “rubies” in the world are actually spinels. Among these legendary “rubies” is the “Black Prince’s Ruby,” a large, irregular 170-carat red spinel cabochon that is set above the Cullinan II diamond at the front of the Imperial State Crown of England. The stone first appeared in historical records of 14th-century Spain, and was owned by a succession of Moorish and Spanish Kings. In 1367, Don Pedro gave it to Edward, Prince of Wales—the “Black Prince”—as payment for a battle victory.
Another famous spinel is the “Timur Ruby”, an engraved 352.50-carat spinel whose colourful trajectory is intricately intertwined with Mughal history on the Indian subcontinent. Successive owners engraved their names on the red gem, which was finally acquired by the Sikh Maharaja of the Punjab, who collected Mughal treasures, including the Koh-i-Noor diamond. When the British annexed the Punjab in 1849, the spinel was given to Queen Victoria and, in 1853, it was made into a necklace by Garrard.
The “Catherine the Great Ruby” is another example of a beautiful spinel. The remarkable 398.72-carat blood-red stone is mounted at the top of the Great Imperial Crown of Russia. This crown was made for her coronation in 1762, and then used for the coronation of all the czars after her, up to the last Czar Nicholas II in 1896.
Spinels—both historic and modern—have also achieved record prices at auctions over the last few years. At the June 2019 Christie’s auction in New York, an Imperial spinel necklace engraved with Mughal titles sold for US$3.015 million. In 2015, at a Bonhams auction in London, the 50.13-carat “Hope Spinel” sold for US$1.47 million. At Christie’s Geneva auction in May 2011, a historic Mughal spinel bead (1131.59 total carat weight) necklace sold for US$5.2 million. The beads were engraved with the titles of various emperors. All of these spinels are thought to be from the ancient mines in a region that is now in the nation of Tajikistan.
The historic Kuh-i-Lal mines in the Pamir Mountains of Tajikistan near the Afghan border are world famous for their spinels. The mines date back to the 7th century, and written records from the 11th century describe the “balas rubies” from these mines. Another historic source for spinel is Myanmar, mostly the iconic Mogok region. While known primarily for its rubies and sapphires, this area also is home to high quality pink and red spinels.
Sri Lanka has also long been known for its spinels, in a variety of colours, including the electric “cobalt blue” spinels. These remarkable blue gems were also discovered in the Luc Yen area in Vietnam in the late 1980s, along with other colours. Today, cobalt blue spinels are one of the hottest gems on the market. Due to their scarcity and high demand, they can command high prices, even up to US$100,000 per carat for those very rare stones over 10 carats.
The late 1980s also saw the discovery of red and pink spinels near Mahenge in Tanzania. While this area offers a palette of colours, Mahenge spinels are known primarily for their saturated pink-red tones. The orangey-red “flame spinels” are also found in this area. Other countries also host spinel deposits, among them Afghanistan, Madagascar, Kenya, Australia and Canada.
Although not common, spinels also exhibit asterism, with four, six, twelve and even eighteen-rayed stars in different colours. The stars are generally sharp and, in nearly all cases, the rays are complete. They are truly fascinating gems.
Geologically speaking, spinel forms in marble, the same as ruby, which is why the two gems are often found together. While ruby and spinel both formed in marble, the composition of the host rock is somewhat different for the two gems. Spinel is hosted in a mixed calcite type with other minerals, including magnesium, while ruby forms in a purer calcite type that is often well crystallized. Some spinels are mined from the primary deposits where they formed, i.e. the marbles. Other gems are found in secondary alluvial deposits, called “gem gravels”, where materials have eroded from the primary deposits and washed downstream. From their rough and tumble travels through the water, these spinels are often rounded and smooth, rather than the octahedral forms found in the primary marble deposits.
While they come from around the world and in different colours, spinels are now fully appreciated for their historical significance, vibrant colours and individual beauty. On these pages are but a few examples of how jewellers are incorporating this colourful gemstone into their creations, where they highlight the sparkle of spinel. (Photos are courtesy of each jewellery brand/ designer unless otherwise indicated.)
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