Wolframite
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Wolframite is an iron, manganese, and tungstate mineral with a chemical formula of WO₄ that is the intermediate mineral between ferberite and hübnerite. Along with scheelite, the wolframite series are the most important tungsten ore minerals. Wikipedia
Crystal system: Monoclinic
Cleavage: Perfect
Color: Grayish to brownish black
Crystal class: Prismatic (2/m); (same H-M symbol)
Crystal habit: Tabular to short prismatic crystals
Formula (repeating unit): (Fe,Mn)WO4
Fracture: Uneven to rough