topaz
| topaz | |
|---|---|
 (size: 4.6 cm × 4.5 cm × 3.1 cm) |
|
| General and classification | |
| other names |
|
| chemical formula | Al 2 [6] [(F, OH) 2 | SiO 4 ] |
|
Mineral class (and possibly department) |
Island silicates with non-tetrahedral anions (Neso subsilicates). |
|
System no. to Strunz and to Dana |
9.AF.35 ( 8th edition : VIII / B.02) 52.03.01.01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group | Pbnm (No. 62, position 3) |
| Lattice parameters | a = 4.65 Å ; b = 8.80 Å; c = 8.39 Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 8th |
| Density (g / cm 3 ) | 3.5 to 3.6 |
| Cleavage | completely after (001) |
| Break ; Tenacity | shell-like, uneven |
| colour | variable, often yellow-brown, blue, violet, red, colorless |
| Line color | White |
| transparency | transparent, translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.606 to 1.629 n β = 1.609 to 1.631 n γ = 1.616 to 1.638 |
| Birefringence | δ = 0.010 |
| Optical character | biaxial positive |
| Axis angle | 2V = 48 ° to 68 ° (measured), 58 ° to 68 ° (calculated) |
| Pleochroism | weak: X = yellow; Y = yellow, purple, reddish; Z = violet, bluish, yellow, pink |
The mineral topaz , also known under the misleading trade names Finder's diamond , Killiecrankie diamond , Mogok diamond , Saxon diamond and slave diamond , is a frequently occurring island silicate with the chemical composition Al 2 [6] [(F, OH) 2 | SiO 4 ]. The fluorine (F) and hydroxide (OH) ions in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral. An F-free OH analog is known as a synthetic compound.
Topaz crystallizes in the orthorhombic crystal system and usually develops well-formed and sometimes very large crystals with short to long prismatic or columnar habit and glass-like gloss on the surfaces. In its pure form it is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, as a result of foreign admixtures, take on a yellow, pink-red to brown-red, violet, light blue and light green color, the transparency decreasing accordingly.
With a Mohs hardness of 8, topaz is one of the hard minerals and serves as a reference value on the Friedrich Mohs scale, which goes up to 10 ( diamond ) . Similar to diamond, however, it is also brittle and after the base surface (001) it is very easy to split with completely smooth fracture surfaces , which is often indicated by cracks in the stone. Irregularly broken topazes have uneven to slightly shell-shaped fracture surfaces .
Etymology and history
According to the Roman naturalist Pliny the Elder , the name Topaz comes from the island of Topazos (probably St. John's Island ), which is located in the Red Sea . In fact, olivine , rather than topaz, was mined there, which has long been confused with topaz. Another explanation leads the name back to the Sanskrit word tapas , which means "fire" or "shine".
In 1740 a topaz called the Braganza diamond was set in the Portuguese crown , believing it was a real diamond .
classification
Already in the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the topaz belonged to the mineral class of "silicates and germanates" and there to the department of " island silicates with non-tetrahedral anions (Neso subsilicates)", where he named the " Topas group "with the system no. VIII / B.02 and the other members Andalusite , Boromullite , Kanonaite , Krieselite , Kyanite , Mullite , Sillimanite and Yoderite .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies topaz in the category of "island silicates (nesosilicates)". However, this is further subdivided according to the crystal structure , so that the mineral is classified in the sub-section “Island silicates with additional anions; Cations in [4] er, [5] er and / or only [6] er coordination ”can be found, where only together with Krieselite the“ Topas group ”with the system no. 9.AF.35 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the topaz to the class of "silicates" and there to the department of "island silicates: SiO 4 groups and O, OH, F and H 2 O". Here he is the namesake of the "Topas group" with the system no. 52.03.01 and the other member Krieselit within the subdivision of " Island silicates: SiO 4 groups and O, OH, F and H 2 O with cations only in [6] coordination ".
Crystal structure
Topas crystallizes orthorhombically in the space group Pbnm (space group no. 62, position 3) with the lattice parameters a = 4.65 Å ; b = 8.80 Å and c = 8.39 Å as well as 4 formula units per unit cell .
properties
Topaz is one of those minerals that are able to form very large and massive crystals. The largest known crystals reached a length of over a meter and a weight of up to 2.5 tons.
Topaz cannot be melted in front of the soldering tube. If topaz is heated to over 1350 ° C, fluorine escapes in the form of SiF 4 and turns into sillimanite and corundum . When heated together with phosphorus salt, hydrogen fluoride (HF) escapes .
Topaz is superficially attacked by pure, concentrated sulfuric acid , so it is decomposed in it. Diluted sulfuric acid, on the other hand, does not damage topaz.
Modifications and varieties
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A well-known variety is pyknite , a straw-yellow, yellowish-reddish or white-gray, stalky topaz aggregate.
Education and Locations
Topaz is found in the form of prismatic crystals grown on the base , but also solid or in a granular variant. It mostly occurs together with beryl , minerals of the tourmaline group and apatite in acid igneous rocks such as granite- associated pegmatites , it also occurs in acid volcanics such as rhyolites or gneisses and as mineral soap, for example in river sediments . In Brazil there are large deposits in which particularly large crystals were found.
The occurrence of wine-yellow crystals in the Schneckenstein in Vogtland was historically particularly significant : this is where the cut topazes of the jewelry of August the Strong (today in the Green Vault in Dresden ) and those in the English royal crown come from. Another important topaz is the great Mughal with 157 ct.
Other locations include Badakhshan , Laghman and Nangarhar in Afghanistan ; Tamanrasset in Algeria ; the region around Mandalay in Myanmar (Burma, English Burma); the island of Honshu in Japan ; several regions in Mexico , Norway , Pakistan and Sweden ; the Lugnez and other regions of Switzerland ; the Central Province and Sabaragamuwa in Sri Lanka ; Czech Republic ; as well as many regions in the US . Topazes have also been found in the eastern region of Antarctica .
Topaz crystals can become very large if the conditions are favorable. Crystals of 100 kg and more are not uncommon. The largest topaz crystal ever found is said to have a length of one meter and a weight of 2,500 kg and was found near Ribáuè , Alto Ligonha in Mozambique . In the Smithsonian Institution two unpolished crystals of 31.8 kg ("Lindsay Topaz") and 50 kg ("Freeman Topaz"), which are also among the largest in the world.
Use as a gem stone
Topaz is a valuable gemstone , but due to its relative abundance, it is not overly expensive even with large, high-quality pieces. Exceptions are the blue topaz, which occurs very rarely in nature, which is also known as "noble topaz", as well as the also rare, orange-red "imperial topaz" or "royal topaz".
Topaz is a difficult stone to work with due to its perfect cleavage after the base surface . Rapid changes in temperature and carelessly carried out barrel work can already lead to cracks and cracks in the stone. He also does not tolerate an ultrasonic bath if he has many inclusions .
Manipulations and imitations
Many topazes are changed in color by treatment. This can be done by irradiation with gamma or electron beams (blue) "Idar-Blue" (brown, greenish-brown) or by heating (blue, reddish). This is how, for example, the dark green, brownish or purple Mystic Fire Topaz (trade name) or the Indian Summer Topaz (trade name), which is pink to light purple, are created.
Despite their name, Madeira and Smoke Topaz are not real topaz minerals. The first is a trade name for citrine or yellow burnt amethyst , the latter is a smoky quartz . All are with the genuine Topas in no way related minerals, but macro crystalline quartz - varieties .
Big and famous topaz
| Surname | gross weight | Found year | Found land | comment |
|---|---|---|---|---|
| "El-Dorado" (also Eldorado ) | 37 kg | 1984 | Minas Gerais , Brazil | Yellowish-brown variety in the “ emerald cut ” with a final weight of 31,000 ct (= 6.2 kg). Exhibited at the Smithsonian Institution (National Museum of Natural History) since 1988 . |
| "Lua de Marabá" ( The moon of Marabá ) | Marabá , Pará, Brazil | Gray variety in "octagon cut" with a final weight of 25,250 ct | ||
| "American Golden" | 11.8 kg | Minas Gerais, Brazil | Yellowish-brown variety in the “pillow cut” with 172 facets, a final weight of 22,892.5 ct (= 4.578 kg) and a size of 17.53 cm × 14.94 cm × 9.34 cm. | |
| "Brazilian Princess" | Brazil | Light blue variety with a "Carré cut" ( square ) with a final weight of 21,005 ct (= 4,201 kg). Exhibited in the National Museum of Natural History of the Smithsonian Institution. | ||
| "Golden Topaz Sphere" | Brazil | Yellowish-brown variety in "ball cut" with a final weight of 12,555 ct (= 2.511 kg). Issued at the Smithsonian Institution | ||
| "Topaz Amarelo" ( Yellow Topaz ) | Brazil | Yellow variety in "pear cut" with a final weight of 9,600 ct (= 1.920 kg) | ||
| "Topaz Azuli" ( Blue Topaz ) | Brazil | "Lively" blue variety in "pillow cut" with a final weight of 8,225 ct (= 1.645 kg) | ||
| Without proper name | Brazil | Yellow variety in an unknown cut shape with a final weight of 7,725 ct. Issued at the Smithsonian Institution. | ||
| Without proper name | Brazil | Colorless variety in "emerald cut" with a final weight of 4,202 ct. | ||
| Without proper name | Brazil | Blue variety in an unknown cut shape with a final weight of 3,273 ct. Issued at the Smithsonian Institution. |
See also
literature
- Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 242, 486 .
- Helmut Schrätze , Karl-Ludwig Weiner : Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 694-697 .
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 677-679 (first edition: 1891).
- 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. 118 .
Web links
- Mineral Atlas: Topaz
- David Barthelmy: Topaz Mineral Data. In: webmineral.com. Retrieved May 19, 2019 .
- Topaz search results. In: rruff.info. Database of Raman spectroscopy, X-ray diffraction and chemistry of minerals (RRUFF), accessed on May 19, 2019 .
- American-Mineralogist-Crystal-Structure-Database - Topaz. In: rruff.geo.arizona.edu. Retrieved May 19, 2019 .
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 548 .
- ↑ a b c d e f Topaz. In: mindat.org. Hudson Institute of Mineralogy, accessed May 19, 2019 .
- ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 66 (List of Misleading Trade Names for Imitation Diamond).
- ↑ B. Wunder, DC Rubie, CR Ross II, O. Medenbach, F. Seifert, W. Schreyer: Synthesis, stability, and properties of Al2SiO4 (OH) 2. A fully hydrated analogue of topaz . In: American Mineralogist . tape 78 , 1993, p. 285–297 ( rruff.info [PDF; 1.7 MB ; accessed on May 19, 2019]).
- ↑ Topaz . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 78 kB ; accessed on May 19, 2019]).
- ↑ Mineral Atlas: Mineral Records
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 678 (first edition: 1891).
- ↑ a b Leopold Rössler: Topas. In: beyars.com. BeyArs, accessed May 19, 2019 . and Leopold Rössler: Königstopas, Imperialtopaz. In: beyars.com. BeyArs, accessed May 19, 2019 .
- ↑ Michael North (ed.): Cultural exchange: Balance and perspectives of early modern research . Böhlau, Cologne, Weimar, Vienna 2009, ISBN 978-3-412-20333-7 , pp. 335 ( limited preview in Google Book search).
- ^ Swiss mineral sites - Minerals in Switzerland: T. In: mineralien-ch.ch. October 24, 2013, accessed May 19, 2019 .
- ↑ List of localities for topaz in the Mineralienatlas and Mindat
- ↑ Mineral Atlas: Mineral Records
- ↑ a b Mineral Gallery: Topaz. In: geogallery.si.edu. Smithsonian National Museum of Natural History. Retrieved May 19, 2019 .
- ↑ Topaz mineral portrait: giant crystals
- ↑ Bernhard brother embellished stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde, Saarbrücken 2005, ISBN 3-89060-079-4 , p. 66 .
- ↑ a b c d e f g h InternetStones.com - Famous faceted topaz gemstones greater than 1,000 carats in weight, arranged in descending order of weights ( Memento from February 1, 2016 in the Internet Archive )
- ^ New York Times - American Museum of Natural History ( Memento January 27, 2013 in the Internet Archive )