Wolframite, Iron, manganese tungstate,
Formula (Fe,Mn)WO₄.

Crystal system: Monoclinic.(crystals usually prismatic and tabular).
Hardness: 5
Density: 7.1 to 7.5 gms/cm³ (Density increases as the iron content increases).
Colour: Brownish-black to black.
Streak: Redrish-brown to black

A complete solid solution series exists between Ferberite, FeWO₄, and Hubnerite, MnWO₄. The name 'Wolframite' is given to minerals having a mixed iron / manganese composition. Wolframite occurs in granite pegmatite veins in association with quartz and in hydrothermal veins commonly in association with pyrite or pyrrhotite. Wolframite is the principal ore of tungsten, a metal used in the manufacture of hard steels and for the filaments of electric light bulbs.

The picture shows two black crystals of wolframite embedded in Quartz. The specimen comes from the Yangangxian Mine, Yizhang, Chengzhou City, Hunan Province, China.