Occurrence
Chalcophanite is known only from Sterling Hill, where it was discovered and described by Moore (108), then chemist for the Passaic Zinc Company. He states that it was found in cavities and fissures in a mass of debris made up of waterworn fragments of quartz and other rocks and of more or less decomposed franklinite, willemite, and zincite. This mass of material was commonly called the "stripping" of the calamine deposit at the Passaic mine and was used to some extent as an ore of manganese.

In 1882 Roepper (124) announced a new hydrous oxide of zinc, iron, and manganese, found at Sterling Hill in the form of octahedrons, and gave to it the name "hydrofranklinite." His investigation was unfinished at his death, but Penfield and Kreider (157), on analyzing similar material, found it to be the same as chalcophanite, its apparent octahedral form being due to the habit of the rhombohedral crystals (figure 56).

Figure 56 Rhombohedral crystal of chalcophanite of octahedron-like habit, showing the forms c(0001) and r(1011). Sterling Hill.

Its composition and mode of occurrence indicate clearly that chalcophanite is an alteration product of franklinite. Moore believed that franklinite was first changed to hydrohetaerolite—2ZnO.2Mn₂O₃.H₂O, the iron being partly eliminated as limonite—and then by oxidation and further hydration the hydrohetaerolite was in turn changed to chalcophanite.⁴ The facts that chalcophanite is invariably found surrounding hydrohetaerolite where the two occur together and that some franklinite crystals, deeply etched, have been found coated in turn by hydrohetaerolite and chalcophanite give strength to Moore's theory of the origin of those peculiar and very local minerals.

⁴ From a note by Moore, appended to a specimen of hydrohetaerolite In the Roebling collection.