Spinel of Mahenge, Tanzania

Spinel is magnesium aluminum oxide with the formula MgAl2O4. The name "spinel" comes from either the Latin word "spina" meaning "thorn", due to its characteristic octahedral crystals having pointed ends, or the Greek word "spintharis" meaning "spark". Although spinel occurs in a range of different colors, the pink to red variety is the one that is commercially important. Spinel is single refractive and doesn't have pleochroism. It belongs to the cubic crystal system with hardness of 8.0 on the Mohs scale.

Spinel offers a range of hues from orange to intense red, vibrant pink, and all shades between purple, blue and violet through to bluish green.

Historically, the most famous red spinels came from the Balas region of Afghanistan and were known as Balas rubies. Some of the most famous rubies in the world, such as the Black Prince's Ruby, part of the British Crown Jewels, are actually spinels. More recently, Sri Lanka and Burma has been the main source for fine spinel. The highest quality transparent blood-red "ruby spinel" and hot-pink spinel has come from mines in Mogok, Upper Burma.

In 2007 several huge spinel crystals were discovered at Ipanko, near the town of Mahenge, in Tanzania. Miners unearthed spinel crystals weighing from six to 54 kg. The crystal was highly included, but large chunks of top quality stone were able to be cobbed off.

The spinel crystal displayed the vibrant pink color that is now famous from Mahenge Spinel. Thousands of carats of gem quality gems were cut in Thailand and distributed into the world market. From this point on Mahenge Spinel was thrust into the world spotlight.

Spinel is highly sought after by gem connoisseurs, and well-formed spinel crystals are in high demand among collectors. Red spinel range from orange-red to purplish red, with pure red considered the finest of all. A top-quality 5 carat red spinel might sell for around a tenth the price of an equivalent-quality ruby, and pink spinel often sells for less than pink sapphire.

Tanzania is now the world's second largest supplier of spinel in the pink-to-red range. Spinel also has been found in Ipanko and Matombo. Since the Mahenge spinel is still a recent discovery, there is still top quality material available for collectors.

Weathered marble outcrops tower over the spinel diggings of Ipanko, near Mahenge.

The Imperial Crown of Russia, also known as the Great Imperial Crown, was made for the Empress Catherine II the Great's Coronation in 1762. The crown is set with around 5000 diamonds from India arranged in a pattern of laurel wreaths and oak branches and a number of fine large white pearls. It is topped with one of the seven historic stones of the Russia's Diamond Collection - a large precious red spinel weighing 398.72 carats. The Imperial Crown of Russia is currently on display in the Moscow Kremlin Armoury State Diamond Fund.

The Imperial State Crown is the most magnificent of all the Crown Regalia. It was made in 1838 for the Coronation of Queen Victoria, and then altered for the Coronation of George VI in 1937 and Elizabeth II in 1953. It is usually worn at the end of the coronation ceremony, when the newly-crowned monarch departs from Westminster Abbey. Although the crown is modern in design, it is set with very old gems. The Black Prince’s Ruby (spinel), roughly 170 carats, is set into the central panel of the crown.