Spinel Properties, Facts and Photos
What is Spinel?
Although spinel gemstones are best known for being red or pink, they can also be blue to mauve, dark green, brown or 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 are found in the same location and have similar 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 the two crystals 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 stone, it's not quite as hard as corundum. On the Mohs scale of hardness, spinel grades 8, while corundum grades 9. The hardest mineral on the scale is diamond, which grades 10.
The basic chemical composition of spinel is aluminium and magnesium. When free from impurities, the gemstone is colourless. Impurities such as chromium, iron and cobalt introduce a variety of colours.
Spinel is known to have been mined as early as 750 to 950 in Badakhshan province, northeastern Afghanistan. Most of the earliest spinels 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 ruby, spinel gemstones are often flawless, hence 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 on display in the Harvard Natural History Museum, Massachusetts, USA. Photo by Stone Mania.
The red spinel in our second picture, which is displayed in the Natural History Museum Los Angeles, is courtesy of Stan Celestian.
The third photo, spinel on calcite from Myanmar, is courtesy of Géry Parent.
Photos are clickable and redirect to the original image.
