scheelite

{{Infobox mineral | name = Scheelite | category = Tungstate mineral | boxwidth = | boxbgcolor =#ee964b | image = Scheelite-224167.jpg | imagesize = 260px | caption = | formula = CaWO4 | IMAsymbol = Sch | molweight = | strunz = 7.GA.05 | system = Tetragonal | class = Dipyramidal (4/m) H-M symbol: (4/m) | symmetry = I41/a | unit cell = a = 5.2429(3), Å c = 11.3737(6) Å; Z = 4 | color = Colorless, white, gray, dark brown, brown, tan, pale yellow, yellow-orange, golden yellow, pale shades of orange, red, green, etc.; colorless in transmitted light and may be compositionally color zoned | habit = Pseudo-octahedra, massive, columnar, granular | twinning = Common, penetration and contact twins, composition plane {110} or {001} | cleavage = On {101}, distinct; on {112}, interrupted; on {001}, indistinct | fracture = Subconchoidal to uneven | tenacity = Brittle | mohs = 4.5–5 | luster = Vitreous to adamantine | refractive = nω = 1.918–1.921, nε = 1.935–1.938 | opticalprop = Uniaxial (+) | birefringence = δ = 0.017 | pleochroism = Definite dichroic in yellow (yellow to orange-brown) | streak = White | gravity = 5.9–6.1 | melt = | fusibility = With difficulty | diagnostic = | solubility = Soluble in alkalis. Insoluble in acids | diaphaneity = Transparent to opaque | other = Fluorescence 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, it fluoresces red under mid-wave UV. | references = }}

Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist Carl Wilhelm Scheele (1742–1786). 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. The semi-precious stone marketed as 'blue scheelite' is actually a rock type consisting mostly of calcite and dolomite, with occasional traces of yellow-orange scheelite.