Ferberite

Ferberite, Boulder, Colorado, USA. A 7×6×3 cm specimen partially covered on one face with small black ferberite crystals; this is the iron-rich variety of what is known as wolframite. In fact, wolframite is not a recognised mineral species, but rather an intermediate form between hübnérite (the manganese-rich variety) and ferberite. Wolframite is in fact an iron-manganese wolframate. Two historical labels, one by J. Chervet and the other by Boubée