Hetaerolite is a zinc manganese oxide mineral related to hausmannite. Few analyses have been published since Palache's (1935) summary. Frondel and Klein found some Fe in exsolved hetaerolite, but most analyses, including unpublished ones by [Dunn], are close in composition to that reported by Criddle and Stanley (1986), who found the material they studied optically to be of near end-member composition.
Hetaerolite was originally described from Sterling Hill by Moore (1877) and was restudied by Palache (1910, 1928) in part to clear up confusion regarding its identity with the Colorado material described by Ford and Bradley (1913). The confused history of this species and hydrohetaerolite is discussed by Palache (1935) and by Frondel and Heinrich (1942) who re-examined both minerals. Local material was described by Mason (1946) and Frondel and Klein (1965). Dasgupta (1974) found a hetaerolite-like phase as an end product of the heating of chalcophanite. Hetaerolite is also known from Franklin but is more abundant at Sterling Hill.
Hetaerolite occurs as massive material, exsolved plates, and well-formed crystals. The crystallizing power of hetaerolite is strong, and euhedral crystals, most less than 2 mm in size, dipyramidal and pseudo-octahedral in habit, are the common mode of occurrence. The fiveling twins illustrated by Palache (1935) are exceedingly rare; [Dunn] has seen none but has observed a fluorite fiveling which was nearly identical to the drawing. Hetaerolite is black, opaque, and has metallic to submetallic luster. The density is 5.18 g/cm3. The cleavage is imperfect.
Exsolutions of hetaerolite in franklinite were found by Ramdohr and studied by Mason (1946) and by Frondel and Klein (1965), who also described the chemical system, as did Mason (1947). This occurrence of hetaerolite exsolved in franklinite is of major petrologic significance.
[Dunn] has found hetaerolite as an exsolution on parting planes in zincite; such a relation may account for some of the Mn2O3 reported in early analyses of zincite. This exsolution, evident as thin black films on zincite partings, is quite common, indeed abundant. In specimens wherein such zincite has been dissolved away naturally, hetaerolite remains as parallel to subparallel platelets resembling shelves in remnant vugs, upon which secondary zincite, hodgkinsonite, or willemite may be crystallized. An inclusion of hetaerolite within zincite (not stated to be an exsolution) was reported by Squiller (1976) to have near end-member composition.
Optically hetaerolite was studied by Larsen (1921) who found it to be uniaxial, negative, and provided indices of refraction. Additional optical descriptions and data were given by Orcel and St. Pavlovitch (1931), Ramdohr (1980), Picot and Johan (1982), and Criddle and Stanley (1986, 1993).
Hetaerolite is abundant at Sterling Hill, where it commonly occurs intimately associated with chalcophanite in the Noble and Passaic pits, and in the underlying mud zone, which extends to a depth of at 680 feet (207 meters). Here hetaerolite commonly occurs as small crystals and comprises part of the rounded and sometimes stalactitic masses of chalcophanite and Mn-oxides.
Hetaerolite is also known from both Franklin and Sterling Hill as small secondary crystals, both isolated and as druses, in seams and veins, generally accompanying Mn-Zn minerals such as hodgkinsonite and chlorophoenicite, and also associated with hemimorphite, zincite, and carbonates. It is quite likely that much hetaerolite has gone unrecognized, mislabeled as franklinite in Fe-poor secondary assemblages. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg (Type Locality)
 Year Discovered: 1877
 Formula: ZnMn2O4
 Essential Elements: Manganese, Oxygen, Zinc
 All Elements in Formula: Manganese, Oxygen, Zinc
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
 To find out more about this mineral at minDat's website, follow this link   Hetaerolite

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.597

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.61

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 15, No. 1 - February 1974, pg. 11Research Reports - Hetaerolite (small article)
View IssueV. 9, No. 1 - February 1968, pg. 14The Exclusive Minerals of Franklin/Ogdensburg, N.J. (as of January 1968) by Frank Z. Edwards - Hetaerolite (Short Note)

Hetaerolite crystals, calcite, and minor zincite, from Sterling Hill Mine, NJ
Hetaerolite crystals (black), calcite (white), and minor zincite (brown to reddish brown), from Sterling Hill Mine, NJ. Photo by Robert A. Boymistruk.

All content including, but not limited to, mineral images, maps, graphics, and text on the Franklin-Ogdensburg Mineralogical Society, Inc. (FOMS) website is licensed under a
Creative Commons Attribution-NonCommercial 4.0 International License.
Creative Commons License