Mineral of the Month: The Wolframite Series
Bob Farrar
The Mineral of the Month for November will be wolframite. Wolframite is of great importance as an ore of tungsten, However, it can also occur as well-developed crystals that are of interest to mineral collectors. Not to be confused with wulfenite, it takes its name from the old word for tungsten, wolfram. Wolframite is no longer considered a single mineral species, but many specimens still carry the name, and it is used in older references, so it can be helpful to learn about it.
Wolframite is actually a series of two minerals, hübnerite and ferberite. The general formula is tungstate of iron and/or manganese, (Fe,Mn)WO4. When iron predominates, the mineral is ferberite. When manganese predominates, it is hübnerite. Of the two, ferberite is more common. Most recent specimens are labeled as either ferberite or hübnerite rather than as wolframite, but pieces labeled as wolframite still turn up. Wolframite crystalizes in the monoclinic system, with crystals that are usually blade-like in form. It varies in color from black to a dark reddish brown. As one might expect from its composition, wolframite is a heavy mineral, with a specific gravity of 7.1 to 7.5. Other physical properties include perfect side pinacoid cleavage, a hardness of 4.0 to 4.5, and a submetallic luster. Distinguishing wolframite from other heavy minerals such as columbite can be difficult and may require chemical tests for tungsten that are beyond the abilities of average collectors. Hübnerite tends to be more brown in color than ferberite. Hübnerite also has some translucence, often visible in thin chips.
Wolframite typically occurs in quartz veins, where it is often associated with other minerals often found in such environments, such as pyrite, fluorite, and sulfosalts. Among the most famous such localities for hübnerite is Pasto Bueno, Peru. Hübnerite is also found at the Sweet Home Mine in Colorado, a locality more famous for its fine rhodochrosite crystals. Fine ferberite crystals, up to 30 cm long, are found at Panasqueira, Portugal, in association with fluorapatite. Excellent specimens of ferberite have been coming out of Hunan Province, China in recent years. Hübnerite and ferberite are found at numerous localities in the Rocky Mountain region of the US, as well as numerous localities in Europe, Asia, and South America.
A little closer to home, there is a major deposit of hübnerite in Vance Co., North Carolina, just south of the Virginia line. This is the Tungsten Queen Mine, also known as the Hamme Tungsten Mine. This mine is now closed due to economic reasons, but large amounts of tungsten ore remain. In its heyday in the early 1970s, it was the largest tungsten mine in North America, and the largest underground mine of any kind in the southeastern US. At this locality there are veins of quartz measuring several meters thick containing blades of hübnerite that measure several centimeters long. Associated with the hübnerite are scheelite, fluorite, galena, sphalerite, and chalcopyrite.
Like many other important ore minerals, many wolframites hold little interest for collectors. However, as is also the case with other ore minerals, hübnerite and ferberite can occur as well-developed crystals, often associated with other interesting minerals, that make great additions to any mineral collection.
Bob Farrar
The Mineral of the Month for November will be wolframite. Wolframite is of great importance as an ore of tungsten, However, it can also occur as well-developed crystals that are of interest to mineral collectors. Not to be confused with wulfenite, it takes its name from the old word for tungsten, wolfram. Wolframite is no longer considered a single mineral species, but many specimens still carry the name, and it is used in older references, so it can be helpful to learn about it.
Wolframite is actually a series of two minerals, hübnerite and ferberite. The general formula is tungstate of iron and/or manganese, (Fe,Mn)WO4. When iron predominates, the mineral is ferberite. When manganese predominates, it is hübnerite. Of the two, ferberite is more common. Most recent specimens are labeled as either ferberite or hübnerite rather than as wolframite, but pieces labeled as wolframite still turn up. Wolframite crystalizes in the monoclinic system, with crystals that are usually blade-like in form. It varies in color from black to a dark reddish brown. As one might expect from its composition, wolframite is a heavy mineral, with a specific gravity of 7.1 to 7.5. Other physical properties include perfect side pinacoid cleavage, a hardness of 4.0 to 4.5, and a submetallic luster. Distinguishing wolframite from other heavy minerals such as columbite can be difficult and may require chemical tests for tungsten that are beyond the abilities of average collectors. Hübnerite tends to be more brown in color than ferberite. Hübnerite also has some translucence, often visible in thin chips.
Wolframite typically occurs in quartz veins, where it is often associated with other minerals often found in such environments, such as pyrite, fluorite, and sulfosalts. Among the most famous such localities for hübnerite is Pasto Bueno, Peru. Hübnerite is also found at the Sweet Home Mine in Colorado, a locality more famous for its fine rhodochrosite crystals. Fine ferberite crystals, up to 30 cm long, are found at Panasqueira, Portugal, in association with fluorapatite. Excellent specimens of ferberite have been coming out of Hunan Province, China in recent years. Hübnerite and ferberite are found at numerous localities in the Rocky Mountain region of the US, as well as numerous localities in Europe, Asia, and South America.
A little closer to home, there is a major deposit of hübnerite in Vance Co., North Carolina, just south of the Virginia line. This is the Tungsten Queen Mine, also known as the Hamme Tungsten Mine. This mine is now closed due to economic reasons, but large amounts of tungsten ore remain. In its heyday in the early 1970s, it was the largest tungsten mine in North America, and the largest underground mine of any kind in the southeastern US. At this locality there are veins of quartz measuring several meters thick containing blades of hübnerite that measure several centimeters long. Associated with the hübnerite are scheelite, fluorite, galena, sphalerite, and chalcopyrite.
Like many other important ore minerals, many wolframites hold little interest for collectors. However, as is also the case with other ore minerals, hübnerite and ferberite can occur as well-developed crystals, often associated with other interesting minerals, that make great additions to any mineral collection.
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Ferberite. Panasqueira, Portugal. Bob Farrar photo and specimen. Hübnerite. Tungsten Queen Mine, Vance Co., North Carolina. Bob Farrar photo and self-collected specimen.