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Tanzanite: description, properties and photo
Tanzanite
Tanzanite is a rare gemstone, a type of mineral zoisite. Only one of its deposits is known in the world – in the north of Tanzania, which was discovered in the middle of the 20th century. The name in honor of the producing country was given to this stone by the president of Tiffany & Co. Henry Platt. The classic color is blue-violet. This color is almost always the result of heat treatment of the stone. Most unheated samples have a brownish color. The most expensive samples are vivid blue. There are also specimens of blue and greenish-blue with a purple hue.
Tanzanite has a characteristic property – the presence of strong pleochroism. You can observe different color shades in the stone, depending on the direction of observation. This property can be used in its identification. Very rare and expensive colors of untreated zoisite are: yellow, orange, pink and green. In faceted form, tanzanites can reach quite large sizes, and now it is not a big deal to find specimens on the world market weighing more than 10 carats, which would be distinguished by good clarity. They are constantly becoming more expensive, and according to the estimates of the mining company, their reserves will last only for the next 20 years. About how to choose a good copy, we tell in the buyer’s guide.
DEPOSITS
The world’s only tanzanite mine is located on the Merelani Plateau in Arusha Province in northern Tanzania. The main mining is carried out underground using eluvial placers formed during the destruction of these rocks. In some areas, the content of tanzanites in 1 ton of ore can reach 60 carats. Tanzanite One Group company was a main producer from 2004. Its reserves will be enough for about 20 years of active development according to estimates.
Properties
Mineral:
zoisite
Chemical formula:
Ca2Al3 (SiO4) 3 (OH)
Crystal Systems:
orthorhombic
Mohs scale hardness:
6-7
Optical character:
Anisotropic
Cleavage:
perfect in one direction
Density:
3.35 g / cm3
Luster:
Vitreous
Refractive index:
1,691-1,700
Birefringence:
0.008-0.013
Dispersion:
0,021
Color:
blue, blue-violet, yellowish green, etc.
Interesting facts
Tanzanite was first discovered in 1967 at the foot of the Kilimanjaro volcano in Tanzania
Tanzanites are mined in only one deposit in the world - on the Merelani plateau in Tanzania..
Tiffany & Co. was involved in promoting the gem to the jewelry podium.
The stone was shot in the Oscar-winning film ‘Titanic’ as the large blue diamond ‘Heart of the Ocean’.
History
The first tanzanite was discovered by the portuguese Manuel de Souza in the summer of 1967. While searching for rubies in the vicinity of Kilimanjaro volcano, he found crystals of blue-violet zoisite, which he mistook for sapphires. Later, the stone caught the eye of the president of Tiffany & Co. Henry Platt, who saw the prospects of new gems, and the company took up their "promotion". At one time, the gem was perceived solely as a substitute for blue sapphires. Tanzanites have become very highly regarded as an independent gem because of its beauty, rarity and proper promotion.
Enhancement
The external properties of the zoisite stone can be changed by man. Almost all tanzanites are subjected to heat treatment at a temperature of 400-650 degrees to give the crystal a rich blue-violet color and eliminate brownish and greenish shades. Unheated tanzanites are rare in the market. They are characterized by light colors with strong pleochroism in blue, purple, green and brownish colors.
Photo
The photo shows faceted tanzanites. Over 10 carats each
In the photo: a sample weighted 24,56 ct
On the photo: stone with a pronounced polychrome property (a combination of several colors)
On the photo: zoisite with a rare natural pink color
