This is a great piece – it is a pseudomorph of pyrite after very elongated, steeply-tapered pyrrhotite, covered with brilliant arsenopyrite crystals. Most of the bright sparkling crystal surfaces visible on this specimen are in fact arsenopyrite. The arsenopyrite crystals are oriented all along the form of each pyrrhotite crystal, indicating that they formed in an epitactic relationship with the pyrrhotite that is now replaced by pyrite. Tiny pyrite crystals are also visible upon close inspection, and black sphalerite crystals are associated as well.
This specimen is from one of a group of pockets found in the late 1970s on the 3rd level of the Inglaterra Mine (equivalent to the 6th level of the Potosi mine) in the West Camp of the Santa Eulalia mining district. It is from the collection of Tracy Kimmel. Tracy acquired it from Andy Seibel, whose label accompanies the specimen. (Note: this label refers to the “Contessa Mine”, but there is no such mine in Santa Eulalia – rather, there is a Condesa Trend of mineralization, and it was exploited by the Inglaterra Mine, but only at levels 0-5, not the 6th level).
An exquisite specimen!