Spinel: Properties, Facts and Photos

What is Spinel?

Spinel is a naturally occurring oxide mineral composed of magnesium and aluminium. It's valued as a gemstone for its hardness, brilliance, and wide range of colours.

Although spinel gemstones are best known for being red or pink, they also occur in shades of blue to mauve, as well as dark green, brown, and black.

For thousands of years, spinel was believed to be ruby or sapphire. The confusion was not only because of the similarity in colour but also because spinels were often found together in the same deposits and have similar physical properties.

As a result, many 'rubies', some of which are now part of crown jewel collections around the world, have turned out to be spinels. The most famous example is the Black Prince's Ruby, set in the British Imperial State Crown.

The work of French mineralogist Jean-Baptiste Louis Romé de l'Isle involved meticulous measurements of crystal angles and faces. By applying these methods, he demonstrated that spinels and rubies have different crystallographic properties.

Identifying the difference between spinel and corundum was a significant advancement in mineralogy because it helped with the classification and identification of gemstones. In 1783, Romé de l'Isle developed a test to distinguish spinels from rubies.

Although spinel is a hard mineral, it's not as hard as corundum. On the Mohs scale of hardness, spinel grades 7.5 to 8, while corundum grades 9.

Spinel is a magnesium aluminium oxide mineral, formed when magnesium and aluminium combine with oxygen during crystallisation. When free from impurities, it's colourless. The presence of chromium, iron, and cobalt introduces the various colours. 

Spinel is known to have been mined as early as 750 to 950 AD in Badakhshan province, northeastern Afghanistan. Most of the earliest stones are likely to have come from here.
Another famous ruby that turned out to be a red spinel is the Timur Ruby. This 352.5 carat stone was part of the late Queen Elizabeth II's collection.  

A 412.25 carat spinel is mounted in the Great Imperial Crown, first used during the coronation of Catherine the Great.

The largest collection of spinel gemstones, which includes one of 500 carats, is part of the Crown Jewels of Iran.

Unlike rubies, spinels tend to have fewer inclusions, so clarity is extremely important.

The Hope Spinel was sold by London Auctioneer Bonhams in 2015. This rare, 50.13 carat, flawless gemstone sold for a record-breaking price of £962,500.

Article Photos

The spinels in our first picture are in the Harvard Natural History Museum, Massachusetts, USA.  Photo: Stone Mania.

The red spinel in our second photo is in the Natural History Museum, Los Angeles. Photo: Courtesy of Stan Celestian.

The third photo, spinel on calcite from Myanmar: Courtesy of Géry Parent.