Scheelite

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Scheelite
Muscovite-Scheelite-tch11a.jpg
Light yellow, pseudo-octahedral scheelite on muscovite from Xuebaoding ( Pingwu district ), China (size: 10.5 cm × 9.6 cm × 9.6 cm)
General and classification
other names
  • Scheel, Scheelerz, Scheelspat
  • Tungstone
  • Heavy stone
  • Tungsten Lime
chemical formula Ca [WO 4 ]
Mineral class
(and possibly department) 		Sulfates (and relatives, see classification )
System no. to Strunz
and to Dana 		7.GA.05 ( 8th edition : VI / G.01)
48.01.02.01
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol tetragonal-dipyramidal; 4 / m
Space group I 4 1 / a (No. 88)Template: room group / 88
Lattice parameters a  = 5.25  Å ; c  = 11.40 Å
Formula units Z  = 4
Frequent crystal faces {112}, {213}, {211}, {114}, {101}
Twinning Complementary twins according to (110) and (100)
Physical Properties
Mohs hardness 4.5 to 5
Density (g / cm 3 ) measured: 6.10 (2); calculated: 6.09
Cleavage clearly according to (101), indistinctly according to (112)
Break ; Tenacity shell-like to uneven; brittle
colour colorless, white, gray, brown, light yellow, yellow-orange, red, green
Line color White
transparency translucent
shine Diamond luster, fat luster
Crystal optics
Refractive indices n ω  = 1.918 to 1.921
n ε  = 1.935 to 1.938
Birefringence δ = 0.017
Optical character uniaxial positive
Other properties
Special features blue-white or orange-colored fluorescence under short-wave UV light

Scheelite , also known as tungstone (Swedish tungsten "heavy stone" or "heavy stone"), is a frequently occurring mineral from the mineral class of " sulfates (including selenates , tellurates , chromates , molybdates and wolframates )". It crystallizes in the tetragonal crystal system with the composition Ca [WO 4 ], so it is chemically a calcium tungstate .

Scheelite mostly develops dipyramidal, pseudo- octahedral crystals of up to 30 centimeters in size with a glass-like to diamond-like sheen on the surfaces. But it also occurs in the form of granular to massive aggregates . In its pure form, scheelite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a gray, brown, light yellow, yellow-orange, red or green color, the transparency decreasing accordingly.

With a Mohs hardness of 4.5 to 5, scheelite is one of the medium-hard minerals that, like the reference mineral apatite (5), can be scratched with a knife .

Etymology and history

The mineral was first mentioned in various mineralogical records in the middle of the 18th century . Among other things, German miners contemptuously referred to it as so-called “white tin barley”, since it was mostly found in association with the cassiterite ( tin stone ), which was mined as tin ore , but did not contain any tin and also behaved as annoying as tungsten in the melting process . In 1760, Axel Frederic Cronstedt introduced the term Tungstein, translated from Swedish , which refers to the high density of around 6.1 g / cm 3 of the mineral.

The analysis of the chemical composition of the mineral turned out to be very difficult due to the high melting point of tungsten and it was not until 1781 that the German-Swedish chemist Carl Wilhelm Scheele succeeded at least in isolating the tungstic acid it contained . Two years later, his students Fausto and Juan José Elhuyar finally succeeded in producing the metal tungsten from this acid.

In Abraham Gottlob Werner's mineral systematics , however, the metal initially received the name Scheel (or Scheelium ) in honor of Scheele, while the mineral was carried under the name Schwerstein . However, both names of Werner did not prevail.

Its designation Scheelite, which is still valid today, was given to the mineral in 1821 by Karl Cäsar von Leonhard . In addition, however, various synonyms such as Scheelerz (after Klaproth ) and Scheelspat (after Breithaupt ) were in circulation.

The “Bispberg” iron mine near Säter in the Swedish province of Dalarnas län is considered the type locality for Scheelite .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the scheelite belonged to the mineral class of "sulfates, chromates, molybdates, wolframates" and to the department of " molybdates and wolframates ", where it was named after the "Scheelite group" “With the system no. VI / G.01 and the other members paraniite (Y) , powellite , stolzite and wulfenite .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns scheelite to the extended class of "sulfates (selenates, tellurates, chromates, molybdates and wolframates)", but also to the Department of "Molybdates and Wolframates". However, this is now further subdivided according to the possible presence of additional anions and / or crystal water , so that the mineral can be found according to its composition in the sub-section "Without additional anions or H 2 O", where it can be found together with fergusonite (Ce) , Fergusonite (Nd) , fergusonite (Y) , formanite (Y) , powellite, stolzite and wulfenite form unnamed group 7.GA.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns scheelite, however, to the class of " phosphates , arsenates and vanadates " and there in the department of "molybdates and wolframates". Here it is only together with Powellit in the "Scheelit series" with the system no. 48.01.02 to be found in the sub-section of " Anhydrous molybdates and tungstates with A XO4 ".

Crystal structure

Scheelite crystallizes tetragonally in the space group I 4 1 / a (space group no. 88) with the lattice parameters a = 5.25  Å and c = 11.40 Å and 4 formula units per unit cell . Template: room group / 88

properties

Small scheelite crystals on quartz under daylight ... ... and UV light
Small scheelite crystals on quartz under daylight ...
... and UV light

Scheelite shows strong, blue-white fluorescence under short-wave UV light , a small addition of molybdenum (including samarium ) changes the color to yellow-orange.

Scheelite is difficult to melt in front of the soldering tube . The phosphorus salt bead turns hot green or yellow in the reduction fire, while cold turns blue.

In hydrochloric acid is scheelite dissolves and separates yellow tungsten (VI) oxide (WO 3 ) from. By adding tin and heating the solution turns blue.

Education and Locations

Scheelite (brown), fluorite (light purple) and quartz (colorless) from the "Yaogangxian" mine in the Yizhang district , China (size: 5.5 cm × 3 cm × 2.5 cm)

Scheelite is formed either through contact metamorphosis under pegmatitic - pneumatolytic conditions or through hydrothermal processes in greisen . In addition to cassiterite, accompanying minerals include apatite , diopside , fluorite , andradite garnets from the grossular series - andradite , quartz , topaz , tremolite , tourmaline , vesuvianite and wolframite .

So far (as of 2012) around 4300 sites for scheelite are known worldwide. One of the most important European deposits is the stratiform scheelite deposit discovered in 1967 in the Felbertal , south of Mittersill in Austria. Similar deposits were later found in Spain and outside Europe at Broken Hill in Australia, in New Mexico (USA), Pakistan and South Korea .

The largest scheelite crystals to date, which were between 9 and 33 cm in size, could be found in various places in Japan. At Kramat Pulai in Malaysia , an octahedral scheelite about 20 cm in size came to light. Crystals up to 15 cm in size were found in Taewha and Tongwha in Korea. The heaviest known crystals with a weight of up to 50 kg were found at Natas in Namibia.

In Germany, the mineral has so far mainly occurred in the Black Forest (Baden-Württemberg), in the Bavarian Fichtelgebirge and Upper Palatinate Forest , in the Hessian Odenwald , in the Harz from Saxony-Anhalt to Thuringia and in the Saxon Ore Mountains .

Other locations are in Afghanistan, Argentina, Australia, Bolivia, Brazil, Bulgaria, Chile, China, Finland, France, Greece, India, Italy, Canada, Kazakhstan, Mexico, Myanmar, Norway, Pakistan, Peru, Poland, Portugal, Russia, Switzerland, Slovakia, Spain, South Africa, the Czech Republic, Turkey, Uzbekistan, the United Kingdom (Great Britain) and the United States of America (USA).

Scheelite could also be detected in rock samples from the moon , which were collected near the landing point of the Luna-20 mission .

use

Scheelite-bearing ore in normal light (above) and short-wave UV light (below).

As a raw material

Along with wolframite, scheelite is the most important ore mineral for the extraction of tungsten. It is usually obtained from raw ore by flotation and enriched in concentrates with more than 65% tungstate. These can be used to extract tungsten . First of all, concentrated hydrochloric acid is used to break down into tungsten (VI) oxide, which can be further reduced to elemental tungsten with hydrogen at 800 ° C. Scheelite is also used to represent tungstic acid.

As a gem

cut Scheelite

Scheelite is one of the lesser-known gemstones , but despite its relatively low hardness it is occasionally ground, as it looks very similar to the more valuable gemstones chrysoberyl (golden beryl), diamond and zircon .

See also

literature

  • KC von Leonhard : Scheelite. In: Handbuch der Oryktognosie. Verlag Mohr and Winter, Heidelberg 1821, pp. 594-596 ( rruff.info PDF 233 kB; p. 2).
  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 619, 620 .
  • Walter Schumann: Precious stones and gemstones. All species and varieties in the world . 13th, revised and expanded edition. BLV Verlags GmbH, Munich / Vienna / Zurich 2002, ISBN 3-405-16332-3 , p. 212 (first edition: 1976).

Web links

Commons : Scheelite  - collection of images, videos and audio files

Individual evidence

  1. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 312 .
  2. ↑ a b c Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 336 .
  3. ↑ Webmineral - Scheelite (English).
  4. ^ A b c 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.  419 .
  5. ^ A b Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  601-406 .
  6. ↑ Scheelite. In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America. 2001 ( handbookofmineralogy.org PDF 63.5 kB).
  7. ↑ a b c d Mindat - Scheelite.
  8. ↑ Inspector Werner's mineral system published by CAS Hoffmann with his permission . In: CAS Hoffmann (Ed.): Bergmannisches Journal . tape  1 , 1789, pp. 369–398 ( rruff.info [PDF; 1.8 MB ] p. 19 with note p. 31).
  9. ↑ Mineralienatlas - Bispberg iron mine.
  10. ^ Paul Ramdohr , Hugo Strunz : Klockmanns textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp.  619, 620 .
  11. ↑ Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th fully revised and updated edition. Springer Verlag, Berlin et al. 2005, ISBN 3-540-23812-3 , pp. 271 .
  12. ↑ Peter C. Rickwood: The large largest crystals. In: American Mineralogist.
  13. ^ Petr Korbel, Milan Novák: Mineral Encyclopedia . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 151 .
  14. ↑ a b MinDat - Localities for Scheelite (English).