structural:summarization, information:highlighting
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 (Fe,Mn)WO, a solid solution of the two minerals ferberite (FeWO) and hübnerite (MnWO), while scheelite is calcium tungstate (CaWO). Other tungsten minerals range in their level of abundance from moderate to very rare, and have almost no economic value.