Scheelite
General
Category	Mineral
Formula	Calcium tungstate - CaWO4
Identification
Colour	Golden yellow, brownish green, brown, pinkish to reddish gray, colourless
Habit	Pseudo-octahedra, massive, columnar, granular
System	Tetragonal
Cleavage	Distinct, two directions
Fracture	Subconchoidal to uneven - brittle
Hardness	4.5-5
Lustre	Vitreous to adamantine
RI	1.918–1.937 (DR +0.016)
Pleochroism	Definite dichoric in yellow (yellow to orange-brown)
Streak	White
SG	5.9–6.1
Fusibility	With difficulty
Solubility	Soluble in acids

Scheelite is a calcium tungstate mineral with the chemical formula CaWO₄. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheelite has been synthesized via the Czochralski process; the material produced may be used to imitate diamond, as a scintillator, or as a solid state lasing medium. Scheelite (Calcium Tungstate) Source: US Government File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Minerals are natural compounds formed through geological processes. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... Rose des Sables (Sand Rose), formed of gypsum crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... A fracture is the separation of a body into two, or more, pieces under the action of stress. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... Minerals are natural compounds formed through geological processes. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Fusibility is the ease with which a material will melt. ... A substance is soluble in a fluid if it dissolves in that fluid. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... The tungstate ion is WO42-. A tungstate (compound) is a compound containing the tungstate ion, or more complicated polymeric ions. ... Minerals are natural compounds formed through geological processes. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ... General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Atomic mass 183. ... Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... Synthesis (from the ancient Greek σύν (with) and θεσις (placing), is commonly understood to be an integration of two or more pre-existing elements which results in a new creation. ... The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors (e. ... Due to its low cost and close visual likeness to diamond, cubic zirconia has remained the most gemologically and economically important diamond simulant since 1976. ... A scintillator is a device or substance that absorbs high energy (ionizing) electromagnetic or charged particle radiation then, in response, fluoresces photons at a characteristic Stokes-shifted (longer) wavelength, releasing the previously absorbed energy. ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... A laser system generally consists of three important parts: An energy source (usually referred to as the pump or pump source); A gain medium or laser medium; A mirror, or system of mirrors, forming an optical resonator. ...

Properties

Its crystals are in the tetragonal crystal system, appearing as dipyramidal pseudo-octahedra. Colours include golden yellow, brownish green to dark brown, pinkish to reddish gray, and colourless. 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. Aside from pseudo-octahedra, scheelite may be columnar, granular, tabular or massive in habit. Twinning is also commonly observed and crystal faces may be striated. Scheelite streaks white and is brittle. In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... For the file system called Lustre, see Lustre (file system) Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... A fracture is the separation of a body into two, or more, pieces under the action of stress. ... Conchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... It has been suggested that twin boundary be merged into this article or section. ... Minerals are natural compounds formed through geological processes. ...

Gems cut from transparent material are fragile yet attractive: 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. Owing to low hardness, however, cut scheelites are best enjoyed unset as valuable collector's pieces. The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Dispersion of a light beam in a prism. ... For other uses, including the shape â—Š, see Diamond (disambiguation). ...

Rockhounds treasure scheelite for its fluorescent properties: under shortwave ultraviolet light, the mineral glows a bright sky-blue. The presence of molybdenum trace impurities occasionally results in a green glow. Rockhounding is the recreational collecting of rocks and/or mineral specimens from their natural environment. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ... Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Atomic mass 95. ...

Occurrence

Scheelite is associated with wolframite in placer deposits and forms in pegmatites, hydrothermal veins, and areas of contact metamorphism. Other associated minerals include fluorite, muscovite, dolomite and molybdenite. Its type locality is the Bisperg iron mine in Säter, Dalecarlia, Sweden. Officially recognized in 1821, scheelite was named after Swedish chemist Carl Wilhelm Scheele, the discoverer of tungsten. Wolframite (Fe,Mn)WO4, is an iron manganese tungstate mineral that is the intermediate between ferberite (Fe2+ rich) and huebernite (Mn2+ rich). ... In geology, a placer deposit is a deposit of earth, sand, or gravel, containing valuable minerals in particles, especially by the side of a river, or in the bed of a mountain stream. ... Pegmatite is a very coarse-grained igneous rock that has a grain size of 20 mm or more; such rocks are referred to as pegmatitic. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Metamorphism can be defined as the mineralogical, chemical and crystallographic changes in a solid-state rock, i. ... Fluorite (also called fluor-spar) is a mineral composed of calcium fluoride, CaF2. ... Muscovite layer Muscovite, also known as potash mica, is a phyllosilicate mineral of aluminium and potassium with formula: KAl2(AlSi3O10)(F,OH)2. ... Dolomite crystals from Touissite, Morocco Dolomite is the name of both a carbonate rock and a mineral consisting of calcium magnesium carbonate (formula: CaMg(CO3)2) found in crystals. ... Molybdenite is a mineral of molybdenum disulfide, MoS2. ... In scientific classification, a type is a specimen or description that corresponds to a taxon (a group of organisms), and helps to identify which organisms may be referred to with that name. ... Säter is a Municipality in Dalarna County, in central Sweden. ... Dalecarlia, or Dalarna, is a historical Province or landskap in the west of middle Sweden. ... The coronation banquet for George IV 1821 was a common year starting on Monday (see link for calendar). ... Chemistry (from the Greek word χημεία (chemeia) meaning cast together or pour together) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms (such as molecules, crystals, and metals). ... Carl Wilhelm Scheele Scheeles house with his pharmacy in Köping. ...

Crystals exceeding 0.5 kilograms (1 pound) have been found in Brazil: Other notable localities include Australia, Austria, Bolivia, Burma, England, Finland, France, Italy, Japan, Sri Lanka, Switzerland and the United States. The Sichuan Province of China has emerged as a newly important source with many "gemmy" specimens recovered. Fine crystals are also found in Tong Wha, Korea. Motto: (French for God and my right) Anthem: Multiple unofficial anthems Capital London Largest city London Official language(s) English Government Constitutional monarchy  - Queen Queen Elizabeth II  - Prime Minister Tony Blair MP Unification    - by Athelstan 927  Area    - Total 130,395 km² (1st in UK)   50,346 sq mi   - Water (%) Population... Sichuan (Chinese: 四川; pinyin: Sìchuān; Wade-Giles: Ssu-ch`uan; non-standard transliteration: Szechwan) is a province in central-western China with its capital at Chengdu. ... Korea (Korean: (ì¡°ì„  or 한국, see below) is a geographic area, civilization, and former state situated on the Korean Peninsula in East Asia. ...

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. Gemmologists 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 obvserved in synthetic scheelite. A round brilliant-cut cubic zirconia Cubic zirconia (or CZ) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. ... Moissanite is a trade name given to silicon carbide (chemical formula SiC) for use in the gem business. ... Gemology (gemmology outside the United States) is the science, art and profession of identifying and evaluating gemstones. ...

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 earths, but the spectrum produced is unlike that of natural stones. Electromagnetic radiation may be characterised by its wavelength. ... A spectroscope is a device which measures the spectrum of light. ... For other meanings of the abbreviation Pr or PR, see Pr and PR. General Name, Symbol, Number praseodymium, Pr, 59 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Atomic mass 140. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Atomic mass 144. ... A dopant, also called doping agent and dope, is an impurity element added to a semiconductor lattice in low concentrations in order to alter the optical/electrical properties of the semiconductor. ... A rare earth is an oxide of a rare earth element. ...

References

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