Dims: 5.1" x 4.8" x 2.2" (13.0 x 12.2 x 5.6 cm)
Wt: 2 lbs., 13.3 oz. (1.282 kg)
Hulcani Mine, Ancash, Peru
This large specimen consists of a crust made up of tiny metallic Franckeite needles mixed with small cubo-octahedral galena crystals. The Franckeite needles are too small to study easily; one will need at least 30-power magnification to effectively study their triclinic form, as they do not exceed 3 mm in length, and their diameters are smaller than 1 mm. Their gray color and metallic luster makes them rather difficult to determine amidst the somewhat warped galenas. It is evident, though, that there is a large amount of Franckeite present. The crust that they constitute grows out of a slab of base rock that is made up of more massive forms of several different metallic sulfide minerals. There is definitely a lot of galena in it, as well as a noticeable amount of either pyrite or chalcopyrite. The slab's underside is lightly sprinkled with what I believe are many tiny sphalerites. I had never even heard of this mineral until I came across this specimen!