Scheelite

The mineral now called scheelite carried, for most of its early history, the name that today belongs to a chemical element. The Swedes called it tungsten — Swedish for heavy stone — because a crystal of it weighed far more than its size suggested. The terminology has been untangling itself ever since.

The mineral was first described in 1751, at Mount Bispbergs klack near Säter, in the Swedish province of Dalarna. At that point it was a curiosity — a dense, pale, well-formed crystal with no known purpose and an awkward name shared with no other substance.

That changed in 1781. The Swedish chemist and apothecary Carl Wilhelm Scheele dissolved the mineral in acid and recovered a new oxide, which he called tungstic acid. He had proved that the heavy stone contained an element no one had isolated. Two years later, in 1783, the Spanish chemists Juan José and Fausto Elhuyar reduced that acid with charcoal and obtained the metal itself.

This is where the names tangle. In English, the metal kept the Swedish word tungsten — even though the Swedes themselves used that word for the mineral, not the element. In German, Spanish, French and most Slavic languages, the metal is wolfram, after another tungsten ore called wolframite. The symbol W on the periodic table, introduced by the chemist Jöns Jacob Berzelius, preserves the wolfram lineage in chemistry worldwide.

The mineral itself needed a new name. In 1821, the German mineralogist Karl Caesar von Leonhard proposed scheelite, posthumously honouring Scheele. Leonhard's name held, and the older Swedish tungsten moved entirely to the element.

For the rest of the 19th century scheelite remained a curiosity of mineral cabinets. It acquired commercial value in the 20th century, when tungsten metal became used in alloy steels and in the filaments of electric lamps.

Scheelite is an important ore of tungsten. Its industrial life today is, almost entirely, the industrial life of the metal it carries.

The dominant use of tungsten, accounting for roughly half of global consumption, is tungsten carbide in cemented carbides. These are wear-resistant composites — also called hardmetals — in which hard carbide grains are held together by a metallic binder. The result is a cutting edge that lasts: drill bits, machining tools and gauges, and the dies used by the metalworking, mining and construction industries. When a metalworking, mining or construction operation needs something harder than steel and tougher than a ceramic, it reaches for tungsten carbide.

Tungsten metal goes into a second tier of demanding applications. Drawn into fine wire, it forms the electrodes used in welding and the filaments still found in some specialty lamps. Alloyed into tool steels, it produces cutting steels that hold their hardness even when red-hot from friction. Alloyed into superalloys, it strengthens the turbine blades of jet engines and the components of rocket-engine nozzles, where temperatures push other metals toward creep.

Two further uses lean on tungsten's exceptional density. Heavy-metal alloys are cast or sintered for armaments, heat sinks, counterweights and other high-density applications. Tungsten chemical compounds, meanwhile, serve as catalysts, inorganic pigments and high-temperature lubricants.

Scheelite also has a use that does not require extracting the metal at all. The mineral fluoresces under ultraviolet light, and that response is exploited in phosphors — scintillators for X-ray and gamma-ray detection, and fluorescent lighting that converts ultraviolet to visible light.

Supply is the awkward part of the story. China produced more than 80 percent of the world's mined tungsten in 2016 and holds nearly two-thirds of known reserves. One of the largest scheelite mining operations sits in Luoyang, in central China.