Scheelite
Calcium tungstate mineral, ore of tungsten, named after Carl Wilhelm Scheele.
Scheelite is a calcium tungstate mineral (CaWO₄) and a major source of tungsten. It was named after the Swedish chemist Carl Wilhelm Scheele. Collectors prize well-formed crystals, and flawless pieces are sometimes cut into gemstones. The mineral can be synthesized using the Czochralski method, producing material used as a diamond simulant, a scintillator, or a solid-state laser medium. Historically, it was employed in radium paint, much like zinc sulfide. Thomas Edison also created a fluoroscope with a calcium tungstate-coated screen that produced images six times brighter than those using barium platinocyanide—the substance that enabled Röntgen's discovery of X-rays. The gemstone marketed as "blue scheelite" is actually a rock composed mainly of calcite and dolomite, with only traces of yellow-orange scheelite. Scheelite crystals belong to the tetragonal system, often forming dipyramidal pseudo-octahedra. Colors include golden yellow, brownish green to dark brown, pinkish to reddish gray, orange, and colorless. It ranges from translucent to transparent, with highly lustrous (vitreous to adamantine) faces. It has distinct cleavage, a subconchoidal to uneven fracture, a high specific gravity of 5.9–6.1, and a low hardness of 4.5–5. Habits include pseudo-octahedral, columnar, granular, tabular, and massive forms. Druzes are rare, found almost exclusively at Cínovec, Czech Republic. Twinning is common, and crystal faces may be striated. The streak is white, and the mineral is brittle. Cut gems are fragile. Its refractive index (1.918–1.937, uniaxial positive, max birefringence 0.016) and dispersion (0.026) are moderately high, giving it strong luster and noticeable "fire" approaching that of diamond. Under shortwave ultraviolet light, scheelite fluoresces bright sky-blue; molybdenum impurities can cause a green glow.
- chemical_formula
- CaWO4
- crystal_system
- Tetragonal
- hardness
- 4.5–5
- specific_gravity
- 5.9–6.1
- color
- Golden yellow, brownish green to dark brown, pinkish to reddish gray, orange, colorless
- fluorescence
- Bright sky-blue under shortwave UV; green with molybdenum impurities
Lore & Background
Scheelite, a calcium tungstate mineral with the formula CaWO4, is a significant tungsten ore. Its name honors Swedish chemist Carl Wilhelm Scheele, though the mineral was originally called "tungsten" by the Swedes, meaning "heavy stone," a term later transferred to the metal. The mineral appears in the tetragonal crystal system, often forming dipyramidal pseudo-octahedral crystals, but also occurs in columnar, granular, tabular, or massive habits. Colors range from golden yellow and brownish green to pinkish gray, orange, and colorless, with a vitreous to adamantine luster. It has a high specific gravity of 5.9–6.1, a hardness of 4.5–5, distinct cleavage, and a white streak. Scheelite fluoresces bright sky-blue under shortwave ultraviolet light; molybdenum impurities can cause a green glow, a feature used by geologists to locate gold deposits. It forms in contact metamorphic skarns, high-temperature hydrothermal veins, greisen, and less often in granite pegmatites, typically alongside cassiterite, wolframite, topaz, fluorite, and quartz. Notable occurrences include Caldbeck Fells in England, Cínovec in the Czech Republic, and the Currais Novos mine in Brazil. Synthetic scheelite, produced via the Czochralski process, has been used as a diamond imitation, scintillator, and lasing medium, and Thomas Edison employed calcium tungstate in a fluoroscope that brightened X-ray images.
Reader's Guide
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 images six times brighter than those with barium platinocyanide. Scheelite is widely used in phosphors, particularly in scintillators for X-ray and gamma-ray detection. The second and third iterations of the Cryogenic Rare Event Search with Superconducting Thermometers dark matter detector experiment use calcium tungstate as a scintillator. It is also utilized in fluorescent lighting systems and in some cathode-ray tubes as a phosphorescent screen material. Synthetic scheelite is occasionally offered as natural scheelite, and collectors may be fooled into paying high prices for it; gemologists distinguish natural from synthetic mainly by microscopic examination and absorption spectrum.
Did You Know?
- Scheelite fluoresces bright sky-blue under shortwave ultraviolet light.
- Thomas Edison invented a fluoroscope with a calcium tungstate-coated screen that made images six times brighter than those with barium platinocyanide.
- 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.
- Scheelite was originally called 'tungsten' by the Swedes, meaning 'heavy stone,' before the name was transferred to the metal.
Frequently Asked Questions
Who is Scheelite named after?
The mineral takes its name from Carl Wilhelm Scheele, the Swedish chemist who made significant contributions to early mineralogy and chemistry in the 18th century.
What is Scheelite's chemical makeup?
Scheelite is calcium tungstate, with the formula CaWO₄, and it crystallizes in the tetragonal system.
What does Scheelite look like and how does it fluoresce?
Scheelite occurs in a wide palette—golden yellow, brownish green, dark brown, pinkish to reddish gray, orange, or even colorless. Under shortwave UV light it glows a striking sky-blue, though specimens carrying molybdenum impurities shift to a green fluorescence instead.
What is Scheelite's role in industry and collecting?
As the primary ore of tungsten, Scheelite is a key source of that dense, high-melting-point metal used in alloys and tooling. Well-formed, inclusion-free crystals are also prized by mineral collectors and occasionally cut into gemstones.
How hard and dense is Scheelite compared to other minerals?
Scheelite sits at 4.5–5 on the Mohs hardness scale, making it softer than quartz but harder than apatite. Its specific gravity of 5.9–6.1 gives it a noticeably heavy, dense feel for its size.
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