Scheelite

Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheelite has been synthesized using the Czochralski process; the material produced may be used to imitate diamond, as a scintillator, or as a solid-state lasing medium. It was also used in radium paint in the same fashion as was zinc sulphide, and Thomas Edison invented a fluoroscope with a calcium tungstate-coated screen, making the images six times brighter than those with barium platinocyanide; the latter chemical allowed Röntgen to discover X-rays in early November 1895.

Scheelite
Scheelite-224167
General
CategoryTungstate mineral
Formula
(repeating unit)
CaWO4
Strunz classification7.GA.05
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
H-M symbol: (4/m)
Space groupI41/a
Unit cella = 5.2429(3), Å
c = 11.3737(6) Å; Z = 4
Identification
ColorColorless, white, gray, brown, pale yellow, yellow-orange, pale shades of orange, red, green; may be compositionally color zoned
Crystal habitPseudo-octahedra, massive, columnar, granular
TwinningCommon, penetration and contact twins, composition plane {110} or {001}
CleavageOn {101}, distinct; on {112}, interrupted; on {001}, indistinct
FractureSubconchoidal to uneven
TenacityBrittle
Mohs scale hardness4.5–5
LusterVitreous to adamantine
StreakWhite
DiaphaneityTransparent to opaque
Specific gravity5.9–6.1
Optical propertiesUniaxial (+)
Refractive indexnω = 1.918–1.921, nε = 1.935–1.938
Birefringenceδ = 0.017
PleochroismDefinite dichoric in yellow (yellow to orange-brown)
FusibilityWith difficulty
SolubilitySoluble in alkalis. Insoluble in acids
Other characteristicsFluorescence under short-wave UV is bright blue, bluish white to yellow. Specimens with more molybdenum tend to fluoresce white to yellow, similar to powellite. Occasionally fluoresces red under mid-wave UV.
References[1][2][3][4]

Properties

Its crystals are in the tetragonal crystal system, appearing as dipyramidal pseudo-octahedra. Colors include golden yellow, brownish green to dark brown, pinkish to reddish gray, orange and colorless. Transparency ranges from translucent to transparent and crystal faces are highly lustrous (vitreous to adamantine). Scheelite possesses distinct cleavage and its fracture may be subconchoidal to uneven. Its specific gravity is high at 5.9–6.1 and its hardness is low at 4.5–5.[1] Aside from pseudo-octahedra, scheelite may be columnar, granular, tabular or massive in habit. Druzes are quite rare and occur almost exclusively at Zinnwald, Czech Republic. Twinning is also commonly observed and crystal faces may be striated. Scheelite streaks white and is brittle.

Gems cut from transparent material are fragile. Scheelite's refractive index (1.918–1.937 uniaxial positive, with a maximum birefringence of 0.016) and dispersion (0.026) are both moderately high. These factors combine to result in scheelite's high lustre and perceptible "fire", approaching that of diamond.

Scheelite fluoresces under shortwave ultraviolet light, the mineral glows a bright sky-blue. The presence of molybdenum trace impurities occasionally results in a green glow. Fluorescence of scheelite, sometimes associated with native gold, is used by geologists in the search for gold deposits.

CaWO4
Structure of CaWO4[5]

Occurrence

Scheelite occurs in contact metamorphic skarns; in high-temperature hydrothermal veins and greisen; less commonly in granite pegmatites.[1] Temperature and pressure of formation is between 200 and 500 °C and from 200 to 1,500 bars.[6] Typical mineral association includes cassiterite, wolframite, topaz, fluorite, apatite, tourmaline, quartz, grossularandradite, diopside, vesuvianite and tremolite.[1]

Scheelite usually occurs in tin-bearing veins; and is sometimes found in association with gold. Fine crystals have been obtained from Caldbeck Fells in Cumbria, Zinnwald/Cínovec and Elbogen in Bohemia, Guttannen in Switzerland, the Riesengebirge in Silesia, Dragoon Mountains in Arizona and elsewhere. At Trumbull in Connecticut and Kimpu-san in Japan large crystals of scheelite completely altered to wolframite have been found: those from Japan have been called “reinite.”[7] It was mined until 1990 at King Island, Australia, Glenorchy in Central Otago and Macraes Flat in North Otago and also at The Golden Bar mine at Dead Horse Creek during World War 1 in Nelson, New Zealand. There is a high concentration of Scheelite in Northeast of Brazil, mainly in the Currais Novos mine in Rio Grande do Norte State.[8]

History

Bispbergs klack
Mount Bispbergs klack

Scheelite was first described in 1781 for an occurrence in Mount Bispbergs klack, Säter, Dalarna, Sweden, and named for Carl Wilhelm Scheele (1742–1786).[2] Owing to its unusual heaviness, it had been given the name tungsten by the Swedes, meaning “heavy stone.” The name was later used to describe the metal, while the ore itself was given the name scheelerz or scheelite.[9]

Synthetics

Although it is now uncommon as a diamond imitation (much more convincing products, like cubic zirconia and moissanite have long since superseded it), synthetic scheelite is occasionally offered as natural scheelite, and collectors may thus be fooled into paying high prices for them. Gemologists distinguish natural scheelite from synthetic material mainly by microscopic examination: Natural material is very seldom without internal growth features and inclusions (imperfections), while synthetic material is usually very clean. Distinctly artificial curved striae and clouds of minute gas bubbles may also be observed in synthetic scheelite.

The visible absorption spectrum of scheelite, as seen by a hand-held (direct-vision) spectroscope, may also be of use: most natural stones show a number of faint absorption lines in the yellow region of the spectrum (~585 nm) due to praseodymium and neodymium trace impurities. Conversely, synthetic scheelite is often without such a spectrum. Some synthetics may however be doped with neodymium or other rare-earth elements, but the spectrum produced is unlike that of natural stones.

Notes

  1. ^ a b c d http://rruff.geo.arizona.edu/doclib/hom/scheelite.pdf Handbook of Mineralogy
  2. ^ a b http://www.mindat.org/min-3560.html Mindat.org
  3. ^ http://webmineral.com/data/Scheelite.shtml Webmineral data
  4. ^ Klein, Cornelis and Cornelius S. Hurlbut, Manual of Mineralogy, Wiley, 20th ed., 1985, p. 356 ISBN 0-471-80580-7.
  5. ^ Zalkin, A.; Templeton, D.H. (1964). "X-ray diffraction refinement of the calcium tungstate structure". Journal of Chemical Physics. 40: 501–504. doi:10.1063/1.1725143.
  6. ^ Lindgren, W. (1933) Ore Deposits of the Western States, pp. 518, 535
  7. ^ Chisholm, Hugh, ed. (1911). "Scheelite" . Encyclopædia Britannica (11th ed.). Cambridge University Press.
  8. ^ Amstutz, Gerhard Christian et al. (Ed.). Ore Genesis: The State of the Art. Vol. 2. Springer Science & Business Media, 2012, p. 418.
  9. ^  Reynolds, Francis J., ed. (1921). "Scheelite" . Collier's New Encyclopedia. New York: P.F. Collier & Son Company.

References

  • Anderson, B. W., Jobbins, E. A. (Ed.) (1990). Gem testing. Butterworth & Co Ltd, Great Britain. ISBN 0-408-02320-1
Ammonium perrhenate

Ammonium perrhenate (APR) is the ammonium salt of perrhenic acid, NH4ReO4. It is the most common form in which rhenium is traded. It is a white, water-soluble salt. It was first described soon after the discovery of rhenium.

Axel Fredrik Cronstedt

Baron Axel Fredrik Cronstedt (/kroonstet/ 23 December 1722 – 19 August 1765) was a Swedish mineralogist and chemist who discovered nickel in 1751 as a mining expert with the Bureau of Mines. He found the mineral, which Cronstedt described as kupfernickel, in the cobalt mines of Los, Hälsingland, Sweden. This name arises because the ore has a similar appearance to copper (kupfer) and a mischievous sprite (nickel) was supposed by miners to be the cause of their failure to extract copper from it. Cronstedt named it nickel in 1754. He was a pupil of Georg Brandt, the discoverer of cobalt. Cronstedt is one of the founders of modern mineralogy and is described as the founder by John Griffin in his 1827 A Practical Treatise on the Use of the Blowpipe. He remains to this day to be an outstanding idol for young swedes.

Cronstedt also discovered the mineral scheelite in 1751. He named the mineral tungsten, meaning heavy stone in Swedish. Carl Wilhelm Scheele later suggested that a new metal could be extracted from the mineral. In English, this metal is now known as the element tungsten.

In 1753, Cronstedt was elected a member of the Royal Swedish Academy of Sciences.

In 1756, Cronstedt coined the term zeolite after heating the mineral stilbite with a blowpipe flame.

Cadmium tungstate

Cadmium tungstate (CdWO4 or CWO), the cadmium salt of tungstic acid, is a dense, chemically inert solid which is used as a scintillation crystal to detect gamma rays. It has density of 7.9 g/cm3 and melting point of 1325 °C. It is toxic if inhaled or swallowed. Its crystals are transparent, colorless, with slight yellow tint. It is odorless. Its CAS number is 7790-85-4. It is not hygroscopic.

The crystal is transparent and emits light when it is hit by gamma rays and x-rays, making it useful as a detector of ionizing radiation. Its peak scintillation wavelength is 480 nm (with emission range between 380-660 nm), and efficiency of 13000 photons/MeV. It has a relatively high light yield, its light output is about 40% of NaI(Tl), but the time of scintillation is quite long (12−15 μs). It is often used in computed tomography. Combining the scintillator crystal with externally applied piece of boron carbide allows construction of compact detectors of gamma rays and neutron radiation.

Cadmium tungstate was used as a replacement of calcium tungstate in some fluoroscopes since 1940's. Very high radiopurity allows use of this scintillator as a detector of rare nuclear processes (double beta decay, other rare alpha and beta decays) in low-background applications. For example, the first indication of the natural alpha activity of tungsten (alpha decay of 180W) had been found in 2003 with CWO detectors. Due to different time of light emission for different types of ionizing particles, the alpha-beta discrimination technique has been developed for CWO scintillators.Cadmium tungstate films can be deposited by sol-gel technology. Cadmium tungstate nanorods can be synthesized by a hydrothermal process.Similar materials are calcium tungstate (scheelite) and zinc tungstate.

It is toxic, as are all cadmium compounds.

Cookes Creek mine

The Cookes Creek mine is a large open pit mine located in the Pilbara region of Western Australia. The mine is located 30 km northwest of Nullagine and is owned by Hazelwood Resources.Cookes Creek represents one of the largest tungsten reserves in Australia having estimated reserves of 9.5 million tonnes of ore grading 0.16% tungsten. The largest deposit is called the Big Hill Tungsten Deposit. It consists of clean scheelite which is easy to extract.Tungsten was first mined in the area in the 1950s.

Fergusonite

Fergusonite is a mineral comprising a complex oxide of various rare-earth elements. The chemical formula of fergusonite species is (Y,REE)NbO4, where REE = rare-earth elements in solid solution with Y. Yttrium is usually dominant (the species fergusonite-(Y)), but sometimes Ce or Nd may predominate in molar proportion (species fergusonite-(Ce) and fergusonite-(Nd)). All the other rare-earth elements are present in subordinate amount, and tantalum substitutes for some of the niobium. There are Fergusonite-beta-(Nd), Fergusonite-beta-(Y), Fergusonite-beta-(Ce) too, but they are classified as 4.DG.10 in the Nickel–Strunz system. The mineral has tetragonal crystal symmetry and the same structure as scheelite (calcium tungstate, CaWO4), but can be metamict (amorphous) due to radiation damage from its small content of thorium. It is found as needle-like or prismatic crystals in pegmatite. It was named after British politician and mineral collector Robert Ferguson of Raith (1767–1840).

Huttonite

Huttonite is a thorium nesosilicate mineral with the chemical formula ThSiO4 and which crystallizes in the monoclinic system. It is dimorphous with tetragonal thorite, and isostructual with monazite. An uncommon mineral, huttonite forms transparent or translucent cream–colored crystals. It was first identified in samples of beach sands from the West Coast region of New Zealand by the mineralogist Colin Osborne Hutton (1910–1971). Owing to its rarity, huttonite is not an industrially useful mineral.

List of English words of Swedish origin

This is a list of English language words borrowed from the Swedish language. Some may be from other Scandinavian languages such as Danish or Norwegian, or may come from Old Norse when it was a single language.

ångström, often written as "angstrom" (after the Swedish scientist Anders Jonas Ångström)

fartlek, which means "speed play" in Swedish, is a training method that blends continuous training with interval training.

gauntlet (run the..., an eggcorn of Swedish gatlopp)

glogg or glugg, (Swedish term for mulled wine) from glögg, a portmanteau of glödgat vin, meaning heated wine.

gravlax, the shortened form of gravad lax, meaning “buried salmon”

gyttja, a kind of mud

lek (from the Swedish leka, "to play")

lingonberry, from lingon

moped, Swedish shortening of trampcykel med motor och pedaler ("engined bike with motor and pedals")

ombudsman, a person who acts as a trusted intermediary between an organization and some internal or external constituency.

orienteering, from orientering

rutabaga, from Swedish dialectal rotabagge

smorgasbord (from the Swedish smörgåsbord, literally "sandwich table"), which in Swedish either refers to a buffet with very specific types of food, or is used as a metaphor

snus, a type of tobacco product consisting of moist tobacco powder

trapp basalts, or "trapps", stair-shaped rock formations (from the Swedish trappor, "stairs")

tungsten, literally "heavy stone", refers in Swedish to scheelite, a mineral containing tungsten and not the metal itself (Swedish volfram)

varve, an annual layer of sediment or sedimentary rock. Derives from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as Hvarfig lera (varved clay) on the first map produced by the Geological Survey of Sweden in 1862.

yrast, a technical term in nuclear physics that refers to a state of a nucleus with a minimum of energy for a given angular momentum

Nevada State Route 839

State Route 839 is an 18-mile (29 km) road that runs from the Nevada Scheelite Mine to U.S. Route 50. The road is also known as Nevada Scheelite Mine Road.

Powellite

Powellite is a calcium molybdate mineral with formula CaMoO4. Powellite crystallizes with tetragonal - dipyramidal crystal structure as transparent adamantine blue, greenish brown, yellow to grey typically anhedral forms. It exhibits distinct cleavage and has a brittle to conchoidal fracture. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 4.25. It forms a solid solution series with scheelite (calcium tungstate, CaWO4). It has refractive index values of nω=1.974 and nε=1.984.Powellite was first described by William Harlow Melville in 1891 for an occurrence in the Peacock Mine, Adams County, Idaho and named for American explorer and geologist, John Wesley Powell (1834–1902).It occurs in hydrothermal ore deposits of molybdenum within the near surface oxidized zones. It also appears as a rare mineral phase in pegmatite, tactite and basalt. Minerals found in association with powellite include molybdenite, ferrimolybdite, stilbite, laumontite and apophyllite.

Roscoe G. Dickinson

Roscoe Gilkey Dickinson (May 3, 1894 – July 13, 1945) was a U.S. chemist, known primarily for his work on X-ray crystallography. As professor of chemistry at the California Institute of Technology (Caltech), he was the doctoral advisor of Nobel laureate Linus Pauling and of Arnold O. Beckman, inventor of the pH meter.

Dickinson received his undergraduate education at the Massachusetts Institute of Technology and, in 1920, became the first person to receive a PhD from Caltech (which had recently changed its name from Throop College). For his dissertation he had studied the crystal structures of wulfenite, scheelite, sodium chlorate, and sodium bromate. His graduate advisor was Arthur Amos Noyes.

Ruby–Poorman mining district

The Ruby–Poorman mining district in the U.S. state of Alaska produced nearly a half million ounces of gold, all from placer mines. Some of the largest gold nuggets found in Alaska are from the district, which lies along the Yukon River. The placers are mostly deeply buried, and most were originally worked with shafts and drifts. Dozens of creeks in the district were mined, many more bear gold prospects. Cassiterite, platinum, scheelite, allanite, and native bismuth have been recovered along with gold from placer mines in the district.

Russellite

Russellite is a bismuth tungstate mineral with the chemical formula Bi2WO6. It crystallizes in the orthorhombic crystal system. Russellite is yellow or yellow-green in color, with a Mohs hardness of ​3 1⁄2.Russellite is named for the mineralogist Sir Arthur Russell, and the type locality is the Castle-an-Dinas Mine, near St Columb Major in Cornwall, where it was found in 1938 in wolframite.

It occurs as a secondary alteration of other bismuth bearing minerals in tin - tungsten

hydrothermal ore deposits, pegmatites and greisens. It typically occurs associated with native bismuth, bismuthinite, bismite, wolframite, ferberite, scheelite, ferritungstite, anthoinite, mpororoite, koechlinite, cassiterite, topaz, muscovite, tourmaline and quartz.

Scheelite, California

Scheelite was an unincorporated community in Inyo County, California. It was located 3 miles (4.8 km) north-northwest of Mount Tom, at an elevation of 6,929 feet (2,112 m). Scheelite, a tungsten ore, was mined in the neighborhood.

Silver perrhenate

Silver perrhenate is a chemical compound with the formula AgReO4. This compound is isostructural with the mineral scheelite (CaWO4). Silver perrhenate reacts with trimethylsilyl chloride to give the silyl "ester" (CH3)3SiOReO3.

Ternary compound

In inorganic chemistry, a ternary compound is a compound containing three different elements. An example is sodium phosphate, Na3PO4. The sodium ion has a charge of 1+ and the phosphate ion has a charge of 3-. Therefore, three sodium ions are needed to balance the charge of one phosphate ion. Another example of a ternary compound is calcium carbonate (CaCO3). In naming and writing the formulae for ternary compounds, rules are similar to binary compounds.

According to Rustum Roy and Olaf Müller, "the chemistry of the entire mineral world informs us that chemical complexity can easily be accommodated within structural simplicity." The example of zircon is cited, where various metal atoms are replaced in the same crystal structure. "The structural entity ... remains ternary in character and is able to accommodate an enormous range of chemical elements." The great variety of ternary compounds is therefore reduced to relatively few structures: "By dealing with approximately ten ternary structural groupings we can cover the most important structures of science and technology specific to the non-metallics world. It is a remarkable instance of nature's simplexity."

Letting A and B represent cations and X an anion, these ternary groupings are organized by stoichiometric types A2BX4, ABX4, and ABX3. Brackets ([ ]) are used to identify a structure by an enclosed typical ternary compound.

A ternary compound of type A2BX4 may be in the class of olivine, the spinel group, phenakite, [K2Ni F4], [β-K2 SO4], or [Ca F2 O4].

One of type ABX4 may be of the class of zircon, scheelite, barite or an ordered silicon dioxide derivative.

In the ABX3 class of ternary compounds, there are the structures of perovskite (structure), calcium carbonate, pyroxenes, corundum and hexagonal ABX2 types.

Other ternary compounds are described as crystals of types

In organic chemistry, the carbohydrates and carboxylic acids are ternary compounds with carbon, oxygen, and hydrogen. Other organic ternary compounds replace oxygen with another atom to form functional groups.

Tungsten

Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. The name tungsten comes from the former Swedish name for the tungstate mineral scheelite, tung sten or "heavy stone". Tungsten is a rare metal found naturally on Earth almost exclusively combined with other elements in chemical compounds rather than alone. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include wolframite and scheelite.

The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered, melting at 3422 °C (6192 °F, 3695 K). It also has the highest boiling point, at 5930 °C (10706 °F, 6203 K). Its density is 19.25 times that of water, comparable to that of uranium and gold, and much higher (about 1.7 times) than that of lead. Polycrystalline tungsten is an intrinsically brittle and hard material (under standard conditions, when uncombined), making it difficult to work. However, pure single-crystalline tungsten is more ductile and can be cut with a hard-steel hacksaw.Tungsten's many alloys have numerous applications, including incandescent light bulb filaments, X-ray tubes (as both the filament and target), electrodes in gas tungsten arc welding, superalloys, and radiation shielding. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are also often used as industrial catalysts.

Tungsten is the only metal from the third transition series that is known to occur in biomolecules that are found in a few species of bacteria and archaea. It is the heaviest element known to be essential to any living organism. However, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to more familiar forms of animal life.

Tungsten ore

Tungsten ore is a rock from which the element tungsten can be economically extracted. The ore minerals of tungsten include wolframite, scheelite, and ferberite. Tungsten is used for making many alloys.

Tungsten ore deposits are predominantly magmatic or hydrothermal in origin and are associated with felsic igneous intrusions.

Wolframite

Wolframite, (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and hübnerite (Mn2+ rich). Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wolframite is found in quartz veins and pegmatites associated with granitic intrusives. Associated minerals include cassiterite, scheelite, bismuth, quartz, pyrite, galena, sphalerite, and arsenopyrite.

This mineral was historically found in Europe in Bohemia, Saxony, and Cornwall. China reportedly has the world's largest supply of tungsten ore with about 60%. Other producers are Canada, Portugal, Russia, Australia, Thailand, South Korea, Rwanda, Bolivia, the United States, and the Democratic Republic of the Congo.

Wulfenite

Wulfenite is a lead molybdate mineral with the formula PbMoO4. It can be most often found as thin tabular crystals with a bright orange-red to yellow-orange color, sometimes brown, although the color can be highly variable. In its yellow form it is sometimes called "yellow lead ore".

It crystallizes in the tetragonal system, often occurring as stubby, pyramidal or tabular crystals. It also occurs as earthy, granular masses. It is found in many localities, associated with lead ores as a secondary mineral associated with the oxidized zone of lead deposits. It is also a secondary ore of molybdenum, and is sought by collectors.

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