Very cool rock! I am not sure whether to call it a pseudomorph, with the implication of replacement... the specimen is a mass of prismatic crystals in pseudohexagonal form, classic Pyrrhotite, but about half are actually composed of fresh and bright Galena. I think they grew together, with the forces shaping Pyrrhotite dominating the whole event. The back side is covered with little Quartz crystals, coated with micro rhombs of Siderite in herringbone pattern. From the Potosí Mine, Francisco Portillo, West Camp, Santa Eulalia District, Mun. de Aquiles Serdán, Chihuahua.