The element is resistant to ordinary acids and aqua regia but dissolves in a mixture of hydrofluoric and nitric acids. It forms compounds with carbon, chlorine, oxygen, sulfur, and some other elements. It forms tungstic acid (H2WO4), or wolframic acid, which is the basis of a series of salts called tungstates, or wolframates.

Tungsten metal is used extensively for filaments for light bulbs and electronic tubes. Carboloy, stellite, and tungsten steels are of importance in industry because they retain their hardness and strength at high temperatures. Tungsten is usually added to steel in the form of ferrotungsten, obtained by the reduction of ferrous tungstate in an electric furnace.

Tungsten carbide is used in place of diamond for dies and as an abrasive. Sodium wolframate is used in the fireproofing of fabrics, in the weighting of silk, and as a mordant in dyeing. Tungsten does not occur uncombined in nature. Large deposits of its ores are found in various parts of the world. The trioxide occurs in nature as the mineral wolfram ochre. Scheelite and wolframite are the chief wolframate minerals. Tungsten is usually prepared from the trioxide by reduction with hydrogen or carbon.



 

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Crystal Description of Scheelite :

Scheelite forms perfect tetragonal dipyramidal crystals that look very much like octahedrons. The crystals may also be truncated with minor pyramids, on the top and/or bottom points of the crystal. Which show Scheelite's true form. Scheelite may also be found in massive and granular form.

Other minerals that form crystals similar to Scheelite include wardite, anatase and powellite. Powellite, CaMoO4, is isostructural with Scheelite which is why it forms similar crystals. The two minerals form a series in which the tungsten of Scheelite is substituted by the molybdenum of Powellite. Powellite fluoresces a yellow color while Scheelite fluoresces a bright blue under short wave ultraviolet light. Of course since molybdenum can substitute for tungsten, some Scheelite specimens will show a yellow fluorescence.

Scheelite crystals can be mistaken as octahedron crystals. So fluorite with it's perfect octahedral cleavage and fluorescence. Can be mistaken for the brownish orange Scheelite. Massive Scheelite has often been mistaken for massive quartz, but then the fluorescence of Scheelite is a dead giveaway.

 

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Uses of Scheelite:

Scheelite is an important source of tungsten,which is a strategically important metal. Scheelite is rarely cut as gemstones. But it is considered as a rare mineral specimen by collectors and good specimens can command very high prices.

Since Scheelite is a primary ore of tungsten we will add some information about tungsten. Tungsten is a very hard, silver-white to steel-gray metal with a body-centered cubic crystalline structure. In its chemical properties it resembles molybdenum.

It is sometimes called wolfram, and it's chemical symbol "W" is taken from this name. When naming compounds of tungsten, use of the name wolfram as a root is preferred. Tungsten is one of the most dense metals and has a higher melting point than any other metal. It melts at about 3,410 deg C and boils around 5,660 deg C. Pure tungsten is ductile, and wires made of it, even those of very small diameter, have a very high tensile strength. 



 

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Scheelite Distinguishing Characteristics:

The fluorescence may be confusing especially when it becomes whitish or yellow from molybdenum substitution, but the high gravity differentiates it from fluorescent fluorite, and the crystals are so common that they will often be seen.

Specimens from worldwide localities show little difference in their color of fluorescence. Unlike other minerals, Scheelite is a "self-activated" mineral. Its fluorescence is due to the mineral itself, rather than some chance chemical impurity. The characteristic blue to bluish white fluorescence of this species is a valuable property in prospecting for Scheelite deposits at night. Old mines have even been reopened when mine shafts were examined with ultraviolet lamps.

Scheelite crystals can be mistaken as octahedron crystals. So fluorite with it's perfect octahedral cleavage and fluorescence. Can be mistaken for the brownish orange Scheelite. Massive Scheelite has often been mistaken for massive quartz, but then the fluorescence of Scheelite is a dead giveaway. 

 

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