What is tungsten? Tungsten is a fine example of an old metal with exciting new uses. It is most familiar as the filament in incandescent lightbulbs. And its primary industrial compound— tungsten carbide—has long been the standard cutting-tool material in steel machining. Today, both tungsten and its carbide have moved beyond their traditional industrial roles. Because of its great density, tungsten has become the preferred material for counterfeiting gold bars, while tungsten carbide’s hardness and polish make it a popular alternative to gold in wedding bands.
What is Tungsten? Properties of the Metal
Tungsten is a brittle, nonreactive, silvery-white metal with a bright, metallic luster. Ranking 59th in crustal abundance, it is about as common as silver. What is tungsten? It is set apart from other metals by its properties, many of which can be described only in superlatives.
With a very high specific gravity of 19.28, tungsten is as dense as gold. And with a Mohs hardness of 7.5, tungsten is the hardest of all metals—harder even than quartz, yet brittle enough to cut with a hacksaw.
Unlike most other metals, tungsten’s lattice structure exhibits both metallic and covalent bonding. A limited degree of metallic bonding explains its relatively poor electrical conductivity. Its strong covalent bonding and close atomic packing account for its great hardness, high density, and extraordinarily high melting point of 6170°F (3410°C). Tungsten’s melting point, three times higher than that of iron, is the highest of any metal and second only to carbon among all elements. Historically, the inability to melt and cast tungsten greatly hindered metallurgical investigation into its properties and potential uses.
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History of Tungsten Discovery
The metal we now know as tungsten first appeared in the historical record in the 1520s when German tin miners were being plagued by a strange, dense mineral that interfered with tin recovery. German scholar Agricola (Georg Bauer) named this unwanted mineral “wolfram,” from the German volf, or “wolf,” and rahm, meaning “cream.” Its name alludes to its troublesome smelter froth that “devoured [combined with] tin like a wolf.” Tungsten was not mentioned again until 1755 when Swedish chemists studied a newly discovered, unusually dense mineral and named it “tung sten,” Swedish for “heavy stone.” In 1781, Swedish chemist Karl Wilhelm Scheele determined that tungsten contained an unidentified metal.
Two years later, Spanish chemist Fausto de Elhuyar, investigating specimens of the old wolfram that had plagued German tin miners two centuries earlier, prepared the oxide of an unfamiliar metal. His initial efforts to isolate the metal produced only a dense, dark, granular material of great hardness that metallurgists today know as synthetic tungsten carbide.
When he finally isolated the elusive metal, de Elhuyar named it “tungsten,” after the Swedish tung sten and named its parent mineral “wolframite” after the old German wolfram. Wolframite is the origin of tungsten’s chemical symbol W.
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Tungsten Minerals and Their Properties
What is tungsten? It is present in only 36 minerals, most of them rare and unusually dense. The most important minerals in abundance, economic value, and collector interest are scheelite, ferberite, and hübnerite. Scheelite (calcium tungstate, CaWO4), the original tungsten, was named for Karl Wilhelm Scheele in 1821. With a Mohs hardness of 4.5-5.0, it crystallizes in the tetragonal system, mostly as dipyramids. Transparent to opaque with a vitreous-to-adamantine luster and a yellow-orange color, scheelite occurs in hydrothermal veins, metamorphic skarns and granite pegmatites.
Consisting by weight of 64 percent tungsten, scheelite is a minor ore of the metal. Collectors prize scheelite for its intense, bright-blue fluorescence under shortwave ultraviolet light. Rockhounds often use portable ultraviolet lights to search for scheelite specimens in mine dumps at night.
Because of its great density (specific gravity 5.9-6.1), scheelite has a high index of refraction (1.92-1.94). Its ability to bend light approaches that of a diamond. With its excellent fire and dispersion, colorless, synthetic scheelite gems served as a popular diamond simulant before the commercialization of cubic zirconia in the 1970s.
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Wolframite Series: Ferberite & Hübnerite
“Wolframite” is no longer a mineral name, but a general term for a solid-solution series with end members ferberite (iron tungstate, FeWO4) and hübnerite (manganese tungstate, MnWO4). In the 1860s, “ferberite” was named for German amateur mineralogist Moritz Rudolph Ferber and “hübnerite” for German mining engineer and metallurgist Adolph Hübner. Both minerals crystallize in the monoclinic system and have a Mohs hardness of 4.5, a submetallic luster, perfect one-directional cleavage, and a high specific gravity of 7.4.
Ferberite usually occurs as black, opaque, prominently striated and elongated prisms. Hübnerite, translucent to opaque with blackish-brown to reddish-brown colors, forms finely striated, flattened prisms and blocky, chisel-shaped crystals. Collectors are most interested in translucent hübnerite crystals that exhibit deep-red, internal reflections.
Both ferberite and hübnerite form in high-temperature veins and to a lesser extent in granite pegmatites. After weathering free from primary deposits, their density allows them to concentrate in secondary alluvial deposits that are sometimes mined as a source of tungsten.
Other Rare Tungsten Minerals
Tungstenite (tungsten disulfide, WS2), a minor ore of tungsten, is gray, opaque and forms hexagonal flakes. Synthetic tungstenite has aerospace applications as one of the few lubricants that are effective in the vacuum of space.
Tungstite (hydrous tungsten trioxide, WO3·H2O) crystallizes in the orthorhombic system and is quite soft at Mohs 2.5. An oxidation product of scheelite, ferberite and hübnerite, it forms bright-yellow, earthy crusts and coatings.
The rare mineral qusongite (tungsten carbide, WC) is found only in Qusong, China. Steel-gray and opaque, it consists of 94 percent tungsten, crystallizes in the hexagonal system, and occurs as tiny grains. With its extraordinary hardness of Mohs 9.5, qusongite is second only to diamond as the hardest of all minerals.
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What is Tungsten Carbide and Industrial Uses
In the 1880s, British metallurgists developed hard iron-tungsten alloys capable of cutting all other types of steel. But tungsten was too costly for commercial use until 1890, when metallurgists learned to smelt scheelite and wolframite-series ores. This new source, coupled with by-product recovery from tin smelting, finally made tungsten affordable to steelmakers.
In 1900, the Bethlehem Steel Company began producing tungsten-steel “hardmetal” cutting tools that retained their sharpness and rigidity even at the extreme temperatures incurred in high-speed lathing. Tungsten-carbide hard metal dramatically reduced the cost of machining steel.
Then in 1927, German metallurgists synthesized tungsten carbide by sintering powdered tungsten and carbon. Powdered tungsten carbide, known as “WC,” is mixed with a cobalt bonding agent, molded, then fired in electric ovens to yield cemented tungsten carbide, a durable material with a Mohs hardness of 9.5. Tungsten carbide quickly became the world’s standard cutting tool material.
We all, often unknowingly, use tungsten carbide every day—in the tiny, wear-resistant roller-ball tips of ballpoint pens. It is about the only material that can withstand the surprising level of roller-ball wear and abrasion produced by everyday writing.
Tungsten Mining Worldwide
Most of the 82,000 tonnes of tungsten now mined worldwide each year comes from ferberite-hübnerite ores. China accounts for 80% of production, followed by Vietnam, Russia and Bolivia. The United States imports its entire 10,000-tonne annual tungsten requirement.
By international convention, tungsten—what is tungsten and how it is mined—is classed as a “conflict mineral,” meaning that proceeds from tungsten mining in certain regions are used to perpetuate wars and human rights violations. Most conflict tungsten comes from the Democratic Republic of the Congo and neighboring Rwanda, where thousands of illegal, artisanal placer miners extract wolframite-group minerals, producing hundreds of tonnes of tungsten each year.
Today, three-quarters of all tungsten is converted to tungsten carbide, while another 15 percent goes into “super-hard” tungsten steel and specialty alloys. The remainder is used in lightbulb filaments, welding electrodes, high-temperature electrical components, ballpoint pens and chemicals for catalytic, pigmentary and lubrication applications.
Highly refined tungsten metal, the type required for lightbulb filaments, now costs $60 per pound. With its great density, one pound of tungsten occupies a volume of only one cubic inch.
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Tungsten in Jewelry and Counterfeiting
In the 1990s, California jewelry designer Trent West began using tungsten carbide in rings that are scratch-proof despite even the roughest everyday wear. Engraved with “WC” or “tungsten carbide” for identification, these neutral, gunmetal-gray rings have the heft of 18-karat gold. Polished with diamond grit, tungsten-carbide rings gleam with a brilliant luster. Often inlaid with gold or platinum, these rings continue to gain popularity as wedding bands. West recently introduced faceted, highly polished tungsten-carbide “gems” as the center “stone” surrounded by small diamonds in gold and platinum rings.
And while tungsten carbide is now seen alongside gold in fine jewelry, metallic tungsten is also counterfeiting gold. Tungsten is a near-ideal counterfeiting agent for gold because of its almost identical density. Tungsten-gold counterfeits first appeared in the 1950s as simple tungsten-copper alloys. With their gold-like color and authoritative heft, they were, at least tactilely and visually, dead ringers for gold. Their only drawback was their easy detectability and much greater hardness.
Today’s sophisticated tungsten-gold counterfeits are much more difficult to detect. Counterfeiters now cast metallic tungsten into standard gold bar forms and then clad these with gold. Their tungsten interiors are detectable only with ultrasound, conductivity tests or by drilling into the bar. In a related technique, counterfeiters drill .999-pure gold bars, pocket the displaced gold, fill the holes with tungsten rods and then restore the gold surface.
What is Tungsten? Final Thoughts
In just over a century, tungsten and its carbide have evolved from lightbulb filaments and cutting tools to durable, scratch-resistant wedding rings. Understanding what is tungsten —its extraordinary hardness, density, and versatility—helps explain why this remarkable metal continues to find new industrial, scientific, and decorative applications. With such unique properties, tungsten is poised for even more innovative uses in the future.
This story exploring what is tungsten previously appeared in Rock & Gem magazine. Click here to subscribe. Story by Steve Voynick.
