| Scheelite | |
|---|---|
 | |
| General | |
| Category | Mineral |
| Chemical formula | Calcium tungstate - CaWO4 |
| Identification | |
| Color | Golden yellow, brownish green, brown, pinkish to reddish gray, colorless |
| Crystal habit | Pseudo-octahedra, massive, columnar, granular |
| Crystal system | Tetragonal |
| Cleavage | Distinct, two directions |
| Fracture | Subconchoidal to uneven - brittle |
| Mohs Scale hardness | 4. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions In Crystallography, the tetragonal Crystal system is one of the 7 lattice Point groups Tetragonal Crystal lattices result from stretching a cubic Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 5-5 |
| Luster | Vitreous to adamantine |
| Refractive index | 1. Lustre (or 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 medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 918–1. 937 |
| Birefringence | +0. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray 016 |
| Pleochroism | Definite dichoric in yellow (yellow to orange-brown) |
| Streak | White |
| Specific gravity | 5. Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. The streak (also called powder color) of a Mineral is the Color of the powder produced when it is dragged across an unweathered surface Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 9–6. 1 |
| Fusibility | With difficulty |
| Solubility | Soluble in acids |
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. Fusibility is the ease with which a material will Melt. Materials such as solder require a low melting point so that when heat is applied to a joint the solder will melt before Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 The tungstate Ion is WO42&minus A tungstate (compound is a compound containing the tungstate ion or more complicated Polymeric A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the It is an important ore of tungsten. An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash 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. The Czochralski process is a method of Crystal growth used to obtain Single crystals of Semiconductors (e This article addresses the many imitations of diamond For a broader discussion of diamonds see Diamond. A scintillator is a substance that absorbs high-energy (ie Ionizing) electromagnetic or charged Particle radiation then in response fluoresces A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. The active laser medium or gain medium is the source of optical Gain within a Laser.
Contents |
Properties
Its crystals are in the tetragonal crystal system, appearing as dipyramidal pseudo-octahedra. In Crystallography, the tetragonal Crystal system is one of the 7 lattice Point groups Tetragonal Crystal lattices result from stretching a cubic A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions Colors include golden yellow, brownish green to dark brown, pinkish to reddish gray, and colorless. Transparency ranges from translucent to transparent and crystal faces are highly lustrous (vitreous to adamantine). Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. Scheelite possesses distinct cleavage and its fracture may be subconchoidal to uneven. Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types A fracture is the (local separation of an object or material 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. Its specific gravity is high at 5. Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 9–6. 1 and its hardness is low at 4. The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 5–5. [1] Aside from pseudo-octahedra, scheelite may be columnar, granular, tabular or massive in habit. In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists Twinning is also commonly observed and crystal faces may be striated. Crystal twinning occurs when two separate crystals share some of the same Crystal lattice points in a symmetrical manner Scheelite streaks white and is brittle. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific
Gems cut from transparent material are fragile yet attractive: Scheelite's refractive index (1. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 918–1. 937 uniaxial positive, with a maximum birefringence of 0. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray 016) and dispersion (0. In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency 026) are both moderately high. These factors combine to result in scheelite's high lustre and perceptible "fire", approaching that of diamond. In Mineralogy, diamond is the allotrope of carbon where the carbon atoms are arranged in Owing to low hardness, however, cut scheelites are best enjoyed unset as valuable collector's pieces.
Rockhounds treasure scheelite for its fluorescent properties: under shortwave ultraviolet light, the mineral glows a bright sky-blue. Rockhounding is the recreational collecting of rocks and/or Mineral specimens from their natural environment Fluorescence is a Luminescence that is mostly found as an Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays The presence of molybdenum trace impurities occasionally results in a green glow. Molybdenum (məˈlɪbdənəm from the Greek word for the metal " Lead " is a Group 6 Chemical element with the symbol Mo
Composition
The scheelite structure consists of isolated tetrahedra. A tetrahedron (plural tetrahedra) is a Polyhedron composed of four triangular faces three of which meet at each vertex. The tetrahedra form (non touching) 1D chains. There are two directions that the "chains" line up. Tungsten deposits only occur where mineralization has taken place at high temperatures and pressures. Research shows these were deposited mostly between 200 to 500 degrees Celsius, and from 200 to 1,500 bars. [2]
Special Characteristics
Scheelite is often found to have a grayish white color; yellowish, brownish or translucent. Its streak is white. Scheelite has a greasy luster which helps distinguish it. Moreover, when looking for scheelite, miners use ultraviolet light which causes it to fluoresce with a bright blue color. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Many prospectors for scheelite have made good use of scheelite's typically bright blue fluorescence by searching for scheelite deposits by night with ultraviolet lamps. Many old mines have even been reopened after examination of the mine shafts with ultraviolet lamps have proven that the ore is not quite yet exhausted. Tungsten can be combined with carbon, and when it does, it forms tungsten carbide. This substance is one of the hardest known other than diamond. This substance is used in abrasive wheels and cutting tools, which the demand for is steadily increasing. [1]
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. Cubic zirconia (or CZ) the cubic crystalline form of Zirconium dioxide ( ZrO2) is a Mineral that is widely synthesized Moissanite or Silicon carbide (SiC is a rare mineral that can be found in meteorites and in terrestrial samples 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. Gemology ( gemmology outside the United States) is the Science, Art and Profession of identifying and evaluating Gemstones Distinctly artificial curved striae and clouds of minute gas bubbles may also be obvserved 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. A material's absorption spectrum shows the fraction of incident Electromagnetic radiation absorbed by the material over a range of Frequencies. A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used Praseodymium (ˌpreɪzioʊˈdɪmiəm or /ˌpreɪsioʊˈdɪmiəm/ is a Chemical element that has the symbol Pr and Atomic number 59 Neodymium (ˌniːoʊˈdɪmiəm is a Chemical element with the symbol Nd and Atomic number 60 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. A dopant, also called doping agent and dope, is an impurity element added to a crystal or semiconductor lattice in low concentrations in order to alter the optical/electrical Rare earth elements and rare earth metals are according to IUPAC, the collection of seventeen Chemical elements in the Periodic table, namely
History
Scheelite was named in 1821 after Carl Wilhelm Scheele (1742-1786). Carl Wilhelm Scheele (9 December 1742 &ndash 21 May 1786 was a German - Swedish pharmaceutical chemist born in Stralsund, Western Pomerania, [3] The Swedish chemist and apothecary, proved the existence of tungstic oxide in the mineral in 1781. Born in Stralsund, Pomerania, he grew up studying chemistry. He then opened a pharmacy where he continued his research and soon made many original discoveries. Some of the papers he wrote were related to many important minerals today such as quartz, alum and clay. He also made many important discoveries not related to minerals such as lactic acid being the source of the acidity of sour milk. His discovery in 1781 was probably his call to fame, where a mineral was named after him. This discovery was about the composition of the mineral Tungsten, later called Scheelite (Calcium Tungstate). From this he obtained tungstic acid, which he is also famous for discovering.
References
- ^ a b University of Arizona State Bureau of Mines. (1975) Bulletin 182, p. 81
- ^ Lindgren, W. (1933) Ore deposits of the western states lindgren, pp. 518, 535
- ^ Klein, C. (2002) The Manual of Mineral Science 23, p. 426
- Anderson, B. W. , Jobbins, E. A. (Ed. ) (1990). Gem testing. Butterworth & Co Ltd, Great Britain. ISBN 0-408-02320-1
- Lindgren, W. (1933) Ore deposits of the western states lindgren, 518, 535, 555.
- University of Arizona State Bureau of Mines. (1975) Bulletin 182, 80-81.
- Mineral Galleries
- Webmineral
- [1]
![[1]](http://www.chemistry.ohio-state.edu/~woodward/ch754/CaWO4.gif){kind=link}
Dictionary
scheelite
-noun
- (mineralogy) A mineral composed of calcium tungstate, with the chemical formula CaWO4; an important tungsten ore.
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