Scheelite
By Bob Farrar
The Mineral of the Month for May is scheelite. Named for Swedish chemist C. W. Scheele, scheelite is a mineral that is important both economically and is interesting to collectors.
Scheelite is calcium tungstate, CaWO4. It crystallizes in the tetragonal system, usually forming bipyramidal crystals though these may be somewhat asymmetrical. It occurs in a broad range of colors, including white, gray, yellow, brown, orange, red, blue, and light green, but cream color to amber are the most common colors. Scheelite is often, but not always, fluorescent, usually blue or yellow. It is a fairly dense mineral, with a specific gravity of 5.9 to 6.1. Other physical properties include a hardness of 4.5 to 5.0, adamantine luster, and bipyramidal cleavage. Crystal form, specific gravity, and fluorescence (if present) are usually sufficient to distinguish scheelite. A chemical test for tungsten can also be used.
Scheelite occurs in a variety of high temperature geological environments, including skarns (calcium-rich silicate rocks), metallic ore deposits, and granitic pegmatites. Among the most famous localities in recent years is Pingwu, Sichuan Province, China. There, spectacular orange crystals up to 15 cm are found in a pegmatite, along with aquamarine and cassiterite. Specimens with both scheelite and aquamarine on the same piece are particularly prized. Scheelite is also found at a number of other Chinese localities, including, recently, the Huanggangliang Mine in Inner Mongolia. It sometimes occurs as a secondary mineral in gold ore deposits, such as the Morro Velho Mine in Minas Gerais, Brazil. Large masses of scheelite, some in the hundreds of kilograms, have been found in some localities, such as the Natas Mine of Namibia, and the Kayb Massif of Kazakhstan. Good crystals have been found at numerous localities around the world, including Korea, Russia, Peru, and several sites in Europe. The United States also produces collectible scheelite specimens. Arizona, in particular, is known for scheelite, including orange crystals to 5 cm from the Cohen Mine, to 10 cm from the Boriana Mine, and to 7 kg in the Dragoon Mountains. It is abundant enough to be mined as tungsten ore at Oreana, Nevada. Other notable western localities are in California and Colorado. In the east, scheelite crystals in matrix have been found at Trumbull, Connecticut. Small amounts of scheelite are found with huebnerite at the Tungsten Queen Mine in North Carolina, but that locality is not considered a major source of scheelite.
Scheelite is important both economically as an ore of tungsten, and as mineral collectors' specimens. It is sometimes faceted as a gemstone, but it is more of a novelty than an important gem mineral. It is due to its occurrence as interesting crystals, sometimes brilliant colors, and fluorescence, however, that make scheelite a mineral that any collector would want to own.
Scheelite is calcium tungstate, CaWO4. It crystallizes in the tetragonal system, usually forming bipyramidal crystals though these may be somewhat asymmetrical. It occurs in a broad range of colors, including white, gray, yellow, brown, orange, red, blue, and light green, but cream color to amber are the most common colors. Scheelite is often, but not always, fluorescent, usually blue or yellow. It is a fairly dense mineral, with a specific gravity of 5.9 to 6.1. Other physical properties include a hardness of 4.5 to 5.0, adamantine luster, and bipyramidal cleavage. Crystal form, specific gravity, and fluorescence (if present) are usually sufficient to distinguish scheelite. A chemical test for tungsten can also be used.
Scheelite occurs in a variety of high temperature geological environments, including skarns (calcium-rich silicate rocks), metallic ore deposits, and granitic pegmatites. Among the most famous localities in recent years is Pingwu, Sichuan Province, China. There, spectacular orange crystals up to 15 cm are found in a pegmatite, along with aquamarine and cassiterite. Specimens with both scheelite and aquamarine on the same piece are particularly prized. Scheelite is also found at a number of other Chinese localities, including, recently, the Huanggangliang Mine in Inner Mongolia. It sometimes occurs as a secondary mineral in gold ore deposits, such as the Morro Velho Mine in Minas Gerais, Brazil. Large masses of scheelite, some in the hundreds of kilograms, have been found in some localities, such as the Natas Mine of Namibia, and the Kayb Massif of Kazakhstan. Good crystals have been found at numerous localities around the world, including Korea, Russia, Peru, and several sites in Europe. The United States also produces collectible scheelite specimens. Arizona, in particular, is known for scheelite, including orange crystals to 5 cm from the Cohen Mine, to 10 cm from the Boriana Mine, and to 7 kg in the Dragoon Mountains. It is abundant enough to be mined as tungsten ore at Oreana, Nevada. Other notable western localities are in California and Colorado. In the east, scheelite crystals in matrix have been found at Trumbull, Connecticut. Small amounts of scheelite are found with huebnerite at the Tungsten Queen Mine in North Carolina, but that locality is not considered a major source of scheelite.
Scheelite is important both economically as an ore of tungsten, and as mineral collectors' specimens. It is sometimes faceted as a gemstone, but it is more of a novelty than an important gem mineral. It is due to its occurrence as interesting crystals, sometimes brilliant colors, and fluorescence, however, that make scheelite a mineral that any collector would want to own.
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