Saturday, December 28, 2013

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.
Historically, the most famous red spinels came from the Balas region of Afghanistan and were known as Balas rubies. Some of the most famous large 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 the Pein Pyit (Painpyit), Bawpadan, Inn Gaung Pyant and Pingutaung mines in Mogok, Upper Burma.

In 2007 several huge spinel crystals were discovered at Ipanko, near the town of Mahenge, in Tanzania. Miners unearthed several large spinel crystals weighing from six to 54 kg.
Though miners have‬‬ searched extensively in the Mahenge area for more of this rare material, this appears to be a one time find. This is not unusual for fine gems. It happened with Kashmir sapphire and Brazilian paraiba tourmaline.

Since the Mahenge spinel is still a recent discovery, there is still top quality material available for collectors.
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.
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.