Tanzanite
| Tanzanite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Ca 2 Al 3 (SiO 4 ) 3 OH |
|
Mineral class (and possibly department) |
see zoisite |
| Similar minerals | Amethyst , cordierite , lazulite , sapphire , spinel |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Physical Properties | |
| Mohs hardness | 6.5 to 7 |
| Density (g / cm 3 ) | 3.2 to 3.4 |
| Cleavage | completely after {100} |
| Break ; Tenacity | uneven, brittle |
| colour | purple, sapphire blue, red-violet, green-yellow |
| Line color | White |
| transparency | transparent |
| shine | Glass luster, mother-of-pearl luster on split surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.691 n β = 1.692 n γ = 1.700 |
| Birefringence | δ = 0.009 |
| Optical character | biaxial positive |
| Pleochroism | very strong: purple, blue and brown or yellow |
| Other properties | |
| Chemical behavior | not acid-resistant |
Tanzanite is a blue variety of the gray to greenish mineral zoisite . Like the pink variety Thulit, it is used exclusively as a gemstone .
Etymology and history
The first discoveries of the transparent, purple-bluish to lilac colored tanzanite were made in 1967 in northern Tanzania . The stone first became known through the New York jeweler Tiffany . He named him after his place of origin Tanzanite, as the name zoisite reminded him too much of the English word for suicide ("suicide").
Education and Locations
Tanzanite is mainly formed from hydrothermal solutions in passages and crevices of gneiss .
The only minable and commercially used deposit of high-quality tanzanite crystals is still in the Gilewy Hills near Arusha in Tanzania . However, the current finds rarely match the outstanding quality of earlier years.
Tanzanite finds have also been reported from the Hindu Kush region in Pakistan , but these stones neither achieve the color quality nor the purity of those from Tanzania and can not be converted into the coveted blue-violet color by firing .
Use as a gem stone
_cut.jpg)
Tanzanite usually occurs in sizes between 0.5 and 10 carats . Larger crystals and tanzanite cat eyes are also rarely found . Two of the largest known tanzanites to date were found in an unspecified pit in Tanzania. The two gemstones each have a length of 30 cm and a thickness of about 10 cm. Weighing in at more than 14 kg (9.27 kg and 5.103 kg), they fetched 7.74 billion Tanzanian shillings (3.35 million US dollars) when sold to the local ministry of mining .
Previously, the 22 centimeter high and 11,000 carat heavy "Kilimanjaro" was considered the larger known tanzanite crystal.
The multicolor ( pleochroism ) of tanzanite in the colors purple, blue and brown or yellow is very pronounced . The larger the stone, the more intense the color. Thanks to its unusual charisma and with the help of the New York jeweler Tiffany, it quickly became one of the most coveted gemstones in the world.
Because of its high transparency, the mineral is very popular as a gem stone and achieves high prices. Due to its pronounced ability to split in one direction, tanzanite not only reacts sensitively to pressure loads such as those occurring during grinding and barrel work , but also to uneven heat loads and rapid temperature changes. Even removing the object to be repaired from the soldering carbon or placing the piece on the soldering sheet or board to cool down can lead to cracks in the stone. The gemstone cannot be cleaned in an ultrasonic device either. It is also sensitive to acids or acid mixtures.
Since tanzanite has a Mohs hardness of 6.5 to 7, which is relatively low for gemstones , which is below that of quartz (7), the sensitivity of the stone must also be taken into account when wearing tanzanite jewelry. Otherwise, rough handling can quickly cause scratches.
Manipulations and imitations
A large part of the commercially available tanzanites is made from gray-brown to yellow-brown zoisites by firing at around 400 to 500 ° C. Firing also intensifies the blue color of weakly colored stones. Tanzanite is also imitated by colored glass (cheap variant) or doublets .
Synthetic tanzanite is still unknown. The “synthetic tanzanite” that is occasionally offered on mineral exchanges is mostly synthetic forsterite .
See also
literature
- Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th, revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 176 .
- Bernhard Bruder: Beautified stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 101 .
Web links
- Mineral Atlas: Tanzanite (Wiki)
Individual evidence
- ↑ a b c d e Jaroslav Bauer, Vladimír Bouška: Gemstone Guide . Verlag Werner Dausien, Hanau / Main 1993, ISBN 3-7684-2206-2 , p. 206 .
- ↑ a b c d e f Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th, revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 176 .
- ↑ a b Gemstone Lexicon - Tanzanite. In: carat-online.at. Retrieved June 25, 2020 .
- ↑ Edelsteinlabor Dieter Pschichholz: Tanzanite (PDF 786 kB) ( Memento from April 7, 2014 in the Internet Archive )
- ↑ Jason Burke: Tanzanian mine owner celebrates discovery of $ 3.3m gemstones. In: theguardian.com. The Guardian , June 25, 2020, accessed June 25, 2020 .
- ↑ Matthias Benz: Merelani Mine - The place where the world famous tanzanite was found. World of Crystals, June 1, 2013, accessed June 25, 2020 .
- ↑ ICA Gem Bureau Idar-Oberstein, Tansanit ( Memento from November 30, 2016 in the Internet Archive )
- ^ Precious stone etiquette from Prof. Leopold Rössler - Tanzanite. In: beyars.com. Retrieved June 25, 2020 .
- ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 101 .