Scheelite

  • Scheel, Scheelerz, Scheelspat
  • Tung stone
  • Heavy stone
  • Tungsten of lime

Scheelite, also known as Tung stone (Swedish: = tungsten heavy stone or heavy rock ), is a commonly occurring mineral from the mineral class of " sulfates (including selenates, tellurates, chromates, molybdates and tungstates ) ". It crystallizes in the tetragonal crystal system with the composition Ca [ WO4 ], and is therefore in chemical terms, a calcium tungstate.

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

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

Special Features

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

Before the blowpipe scheelite is difficult to melt. The salt of phosphorus bead turns hot green or yellow, cold in reducing fire appear blue.

Add hydrochloric acid to dissolve and scheelite separates yellow tungsten ( VI ) oxide ( WO3 ) from. The addition of tin and heating the solution turns blue.

Etymology and history

The first mention of the mineral can be found in the mid -18th century in various mineralogical records. It indicated, among others, German miners disparaged as "white Zinngraupen " because it was usually found in association with degraded as tin ore cassiterite ( tin ore ), but no tin contained and also in the melting process similar annoying behaved like tungsten. 1760, Axel Frederic CRONSTEDT a the translated from Swedish term stays stone, which refers to the high density of around 6.1 g/cm3 of the mineral.

The analysis of the chemical composition of the mineral, however, proved to be due to the high melting point of tungsten is very difficult and only in 1781 succeeded the German - Swedish chemist Carl Wilhelm Scheele at least to isolate the tungsten acid present. His disciples Fausto and Juan José Elhuyar it two years later finally managed to figure out this acid the metal tungsten.

In the mineral systematics of Abraham Gottlob Werner though initially received the metal the name Scheel (or Scheelium ) in honor of Scheele, while the mineral was carried out under the name of heavy stone. However, both terms Werners not prevailed.

Its up today valid name scheelite received the mineral in 1821 by Karl Caesar von Leonhard. In addition, however, were still several synonyms such as, but Scheelerz ( according to Klaproth ) and Scheelspat (after Breithaupt ) in the circulation.

As a type locality for the scheelite iron mine " Bispberg " applies in Sater in the Swedish province of Dalarna County.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the scheelite belonged to the mineral class of " sulfates, chromates, molybdates, tungstates " and then to the Department of " molybdates and tungstates ", where he was named the " Scheelite Group "with the system number. Formed VI/G.01 and the other members Paraniit - (Y), Powellit, Stolzit and Wulfenite.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the scheelite in the extended class of " sulfates ( selenates, tellurates, chromates, molybdates and tungstates ) ," there but also in the Department of " molybdates and tungstates " one. However, this is now further subdivided according to the possible presence of additional anions and / or water of crystallization, so that the mineral according to its composition in the subdivision is "Without additional anions or H2O" to find where it together with fergusonite - (Ce), fergusonite - (Nd), fergusonite - (Y), Formanit - (Y), Powellit, Stolzit and Wulfenite unnamed group 7.GA.05 forms.

The mostly commonly used in English-speaking classification of minerals according to Dana assigns the scheelite contrast, in the class of " phosphates, arsenates and vanadates " and there in the department of " molybdates and tungstates " one. Here it is only together with Powellit in the " scheelite - series" with the system no. 48.01.02 within the sub-division of " water clear with molybdates and tungstates A XO4 " to find.

Education and Locations

Scheelite is either formed by contact metamorphism under pegmatitic - pneumatolytic conditions or by hydrothermal processes in the aged. Accompanying minerals occur in addition to cassiterite, you still apatite, diopside, fluorite, garnets grossular - andradite series, quartz, topaz, tremolite, tourmaline, vesuvianite, wolframite.

Worldwide, so far (as of 2012) around 4300 localities for scheelite known. Among the most important European deposits in 1967 discovered stratiform scheelite deposit is part of the Felbertal, south of Mittersill in Austria. Similar deposits were later found but also in Spain and outside Europe at Broken Hill in Australia, in New Mexico ( USA), Pakistan, South Korea.

The biggest Scheelitkristalle that were 9-33 cm tall, were found in various places in Japan. In Kramat Pulai in Malaysia an octahedral scheelite of around 20 cm size became apparent. Up to 15 cm large crystals occurred in Korea in Taewha and Tongwha. The heaviest known crystals weighing up to 50 kg were found at Natas in Namibia.

In Germany the mineral previously occurred mainly in the Black Forest (Baden- Württemberg), in the Bavarian Fichtelgebirge and the Upper Palatinate Forest, in the Hessian Odenwald, in the Harz Mountains of Saxony -Anhalt, Thuringia and the Saxon Erzgebirge up on.

Other localities lie include 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, Czech Republic, Turkey, Uzbekistan, the United Kingdom ( UK) and the United States of America (USA).

Even in rock samples from the moon, which were collected in the vicinity of the landing point of the Luna -20 mission, scheelite could be detected.

Crystal structure

Scheelite crystallized tetragonal space group I41 / a with lattice parameters a = 5.25 Å and c = 11.40 Å and four formula units per unit cell.

Use

The raw material

Scheelite is the principal ore mineral wolframite next for the recovery of tungsten. It is generally obtained from crude ores by flotation and thereby enriched for concentrates with more than 65% tungstate. They can be used for the recovery of tungsten. This is first digested with concentrated hydrochloric acid to tungsten (VI) oxide which can be reduced to elemental tungsten at 800 ° C with hydrogen. Scheelite is also used to represent the tungstic acid.

As a gemstone

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

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