devoured it like a wolf. This naming follows a tradition of colorful names miners from the Ore Mountains would give various minerals, out of a superstition that certain ones that looked as if they contained then-known valuable metals but didn't were somehow "hexed". Cobalt (c.f. Kobold), pitchblende (c.f. German "blenden" for "to blind" or "to deceive") and nickel (c.f. "Old Nick") derive their names from the same miner's idiom. Occurrence Tungsten has thus far not been found in nature in its pure form. Instead, tungsten is found mainly in the minerals wolframite and scheelite. Wolframite is iron–manganese tungstate , a solid solution of the two minerals ferberite (FeWO4) and hübnerite (MnWO4), while scheelite is calcium tungstate (CaWO4). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economic value. Chemical compounds Tungsten forms chemical compounds in oxidation states from -II to VI. Higher oxidation states, always as oxides, are relevant to its terrestrial occurrence and its biological roles, mid-level oxidation states are often associated with metal clusters, and very low oxidation states are typically associated with CO complexes. The chemistries of tungsten and molybdenum show strong similarities to each other, as well as contrasts with their lighter congener, chromium. The relative rarity of tungsten(III), for example, contrasts with the pervasiveness of the chromium(III) compounds. The highest oxidation state is seen in tungsten(VI) oxide (WO3). Tungsten(VI) oxide is soluble in aqueous base, forming tungstate (WO42−). This oxyanion condenses at lower pH values, forming polyoxotungstates. The broad range of oxidation states of tungsten is reflected in its various chlorides: Tungsten(II) chloride, which exists as the hexamer W6Cl12 Tungsten(III) chloride, which exists as the hexamer W6Cl18 Tungsten(IV) chloride, WCl4, a black solid, which adopts a polymeric structure. Tungsten(V) chloride WCl5, a black solid which adopts a dimeric structure. Tungsten(VI) chloride WCl6, which contrasts with the instability of MoCl6. Organotungsten compounds are numerous and also span a range of oxidation states. Notable examples include the trigonal prismatic and octahedral . Production Reserves The world's reserves of tungsten are 3,200,000 tonnes; they are mostly located in China (1,800,000 t), Canada (290,000 t), Russia (160,000 t), Vietnam (95,000 t) and Bolivia. As of 2017, China, Vietnam and Russia are the leading suppliers with 79,000, 7,200 and 3,100 tonnes, respectively. Canada had ceased production in late 2015 due to the closure of its sole tungsten mine. Meanwhile, Vietnam had