Groups of very brilliant sphalerite crystals showing complex habitus and twins. With an intense luster and deep brown color, near black, with honey reflections. They are peppered by several small but brilliant chalcopyrite crystals. On a siderite matrix, accompanied by dolomite, galena and defined brilliant chalcopyrite crystals. Nowadays, this mine, in the city of Bilbao, is collapsed and it is impossible to get these classic Spanish specimens.