An ore of tungsten (W), the mineral scheelite occurs in localities all over the world. However, gem-quality crystals are rare. Scheelite itself belongs to the scheelite mineral group, which also includes powellite, stolzite, and wulfenite, and forms a series as the W end-member with powellite, the molybdenum (Mo) end-member.
All these materials are rarely seen as faceted gems, but scheelites are probably the most commonly cut of the group. With scheelite’s high dispersion and refractive indices (RI), the right gem design can create lively, sparkly gems with high brilliance. They occur in a wide variety of colors, too. However, the combination of low hardness (4.5-5), distinct and good cleavage, and brittle tenacity makes scheelites poor choices for jewelry use. Nevertheless, collectors prize faceted scheelites for their rarity and beauty. In addition, these gems have extremely bright fluorescence under shortwave (SW) ultraviolet (UV) light and make spectacular specimens.
Before the commercial production of cubic zirconia, scheelite’s dispersion, RI, and colors (including colorless) also made it a good diamond simulant. (Of course, scheelites can look like diamonds but can never match their much greater durability).
Although they typically glow an intense bluish white or whitish blue, scheelites that contain some Mo can fluoresce a creamy yellow in SW. This variety is known as molybdoscheelite. (Powellite, the Mo-dominant series end-member, fluoresces yellowish to golden yellow in both SW and LW UV).
Please note: in a 2001 GIA investigation into new methods for imitating asterism, one of the star stones submitted for analysis was represented as scheelite. However, under further analysis, it proved to be a different species, possibly a samarskite. Nevertheless, the results of this investigation remain relevant. Apparently, these false stars were deliberately and manually created by scratching tightly packed, parallel coarse lines on the domed surfaces of cabochons. Although some specimens looked very convincing, most appeared unnatural, with asymmetrical rays in unusual numbers. The star effects also lacked depth.
While asterism and chatoyancy can occur in scheelites, buyer beware whenever purchasing any gem with a rarely seen optical display.
Synthetic scheelites have industrial uses, especially in laser technology. In the 1960s and 70s, synthetic scheelites were also frequently sold as diamond lookalikes. While no longer commonly used as diamond simulants, faceted synthetic scheelites may still be offered as rare, faceted natural scheelites to unwary collectors.
The colors of synthetic scheelites can vary widely, depending on the rare-earth elements used as dopants. They may show purple, red-brown, pale green, pale yellow, yellow-brown, dark red, and dark yellow-green colors. Without any dopants, synthetic scheelites are colorless.
Gemologists can also use natural or synthetic scheelites to help them distinguish between Type I and Type II diamonds. In a darkened room, they place a scheelite behind a shield with a hole in it. Then, they place a diamond over the hole and shine a SW UV light through it. Type I diamonds are opaque to SW UV light (200 to 280 nm), while Type II are transparent to this light. Thus, if the scheelite shows its dramatic fluorescence, the diamond is a Type II.
Distinguishing Synthetic from Natural Scheelite
Of course, synthetics resemble natural scheelites. However, they may still have some slight differences in the following properties:
Cleavage: None. (Some synthetics may still have Distinct cleavage).
Depending on the rare-earth dopants used, the absorption spectra of synthetic scheelites may differ considerably from those of their natural counterparts. For example, a neodymium-doped purple stone has a distinctive spectrum, with strong lines at 6670 and 4340 and a distinct band at 5690-5590. Some synthetics may not even show absorption spectra.
Notable crystal and gem-quality sources include the following:
United States: Arizona (brown, large crystals, sometimes gemmy); California (colorless gemmy crystals); Connecticut; Nevada; New Mexico; South Dakota; Utah, near Milford (orange crystals, some with clear tips).
Large scheelites are very rare. Some crystals held in museums could yield stones over 100 carats. Smaller, clean gems are available commercially.
Crystals from Arizona, Korea, Peru, and other localities may be very large (4 inches on an edge) and are cuttable in sections. California gems may reach 70 carats. Mexican and Arizona stones usually reach up to about 10 carats, but an orange Mexican stone has been cut over 100 carats. Utah crystals rarely cut stones over 7 carats. Korea has produced crystals up to 13 inches, but none of this size have been cuttable.
You’re more likely to find faceted scheelites in mineral collections than jewelry collections. Such fragile gems would require protective settings, especially as ring stones. Clean scheelites only with a soft brush, mild detergent, and warm water.