Xanthoconite is a monoclinicdimorph of the mineral Proustite. It is a very rare mineral and only forms in very small crystals. Xanthoconite generally forms in the same deposits as Proustite, and may even form together with it in a single matrix. In addition to their differences in crystal symmetry, Xanthoconite usually has a more orange color than Proustite. Xanthoconite is named after a combination of two Greek words: "xanthos", meaning yellow, and "konis", meaning powder, alluding to the yellowish color of this minerals streak.
Xanthoconite is found as a rare mineral in several of the mines where Proustite is found. One of the few regions to produce relatively large crystals that aren't micros are the Freiberg and Schlema Districts, Erzgebirge, Saxony, Germany. Other good localities include the Lengenbach Quarry, Binn Valley, Wallis, Switzerland; the Imiter Mine, Morocco; San Martín, Zacatecas, Mexico; and the Flathead Mine, Kofford Ridge, Flathead Co., Montana.
