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Spinel: description, properties and photo
Spinel
Spinel is a beautiful gemstone with a wide range of color. It has an independent group of minerals. Chemical composition of the mineral is similar to corundums (rubies and sapphires), but differs from them in an isotropic structure. Red gems were previously mistaken for rubies. It was only at the beginning of the 20th century that the truth came to light when properties of a gemstone were distinguished from properties of a ruby by gemological methods. Color range is very diverse and includes pink, red, orange, blue, purple and black. Also there are samples of white, yellow and green tones. Color of spinel depends on the content of impurities of various chemical elements. The most valuable is vivid red color. Rare cobalt content variety of neon blue color is also very much appreciated. That kind of faceted stones are rare in size 1+ carats.
Large gem quality crystals are rare and therefore particularly valuable. High hardness of the gemstone (about 8 on the Mohs scale) allows it to be used in any kind of jewelry.
Vivid colors, strong brilliance, rarity are properties due to which gemstone now competes with rubies and sapphires in beauty and value. It should be noted separately and such a rare property now as the lack of enhancement in most cases. But it must be borne in mind that there is also a synthetic analogue, which is grown by several methods. It is quite difficult to distinguish a synthetic stone from natural spinel. If there is a suspicion that expensive spinel of good color can be synthetic, then it is better to make an expert opinion on this stone in an independent gemological laboratory.
DEPOSITS
Spinel rare forms independent deposits. Often its finds are associated with the manifestations of ruby. It is also found in alluvial places. Some of the best pink and red specimens come from the Mogok area of Myanmar (Burma). From Sri Lanka can come blue variety. In the Pamir in Tajikistan there is a mine of pink and pink-red spinels known since ancient times. Vietnam produces a rare cobalt blue variety, pink and red-violet. Good quality pink and red stones are found in Tanzania. Gem quality specimens are also found in Afghanistan, India, Cambodia, Thailand, Brazil and Australia.
Properties
Mineral:
spinel
Chemical formula:
MgAl2O4
Crystal Systems:
cubic
Mohs scale hardness:
7.5-8
Optical character:
isotropic
Cleavage:
absent
Density:
3.6-4.1 g / cm3
Luster:
Vitreous
Refractive index:
1.712-1.736
Birefringence:
none
Dispersion:
0.026
Color:
pink, red, orange, blue, green, etc.
Interesting facts
Red spinel is the fastest growing colored stone in price now.
It decorated the imperial crowns of Russia, Great Britain, Germany, France and the thrones of the eastern kings.
Some of the best spinels are mined in Mogok, Myanmar (Burma).
Red variety of the mineral was mistaken for ruby until the middle19th century.
History
As a gemstone spinel has been known since ancient times. Red spinels did not differ from ruby before. Traveler Marco Polo, who visited the Pamirs, called the pink Badakhshan stones “rubies of balais”. In Europe this stone was called "balas", according to the ancient name of Badakhshan - «Balas». In France the name “ruby balas” was transformed into “ruby balais”. And when it became clear that this was spinel - “balais spinel”. This stone has always belonged to one of the most expensive gems and was a symbol of power in the royal regalia and adorned the imperial crowns of Russia, Great Britain, France, Germany and the thrones of the Eastern kings. This gem is also decorated russian Grand prince’s “Monomakh's Cap”. A unique sample of 398.72 carats, which had previously decorated the “Monomakh's Cap” is now at the top of the first Russian imperial crown made in 1762 for Catherine II.
Enhancement
Treatment technologies for this mineral are use very rare. It was even believed that spinel is not treated by any kind of methods. It is sometimes possible to fill the cracks with special oils or polymers to visually improve the clarity. Heat treatment may also be used. The impact on the color of the crystal this type of treatment is controversial. The color of the stone does not change in many cases. There is also information that it is possible to brighten dark samples by heat treatment. Pink spinel can become more saturated and sometimes it darkens. Low heat temperature can improve the clarity of crystals containing whitish needle-like rutile inclusions, which dissolve after heating.
Photo
Photo: rough spinel
Photo: Mughal Empire spinel necklace, 1131 carats. Sold in 2011 for 5.214.348 USD
Photo of the Russian Empire crown. The main gemstone is a spinel weighing 398.72 carats
Photo of rough material
Huge gem quality piece of a crystal from Tajikistan
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