HETAEROLITE

ZnMn³⁺₂O₄
Tetragonal, I4/amd, a = 5.754, c = 9.219 Å, Z = 4

	Figure 22-64. Crystal drawings of hetaerolite from Franklin; these are two projections of the same crystal, a “fiveling” twin. Drawings are from Palache (1935) who provided crystallographic data.

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.

Description

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 (Figures 22-66 and 22-67).

	Figure 22-65. Druse of hetaerolite on hodgkinsonite from Franklin. Field of view is 0.7 mm in maximum dimension.

The fiveling twins illustrated by Palache (1935) (Figure 22-64) are exceedingly rare; this writer 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 on {001}, and Frondel and Heinrich (1942) reported {001} and {112} as being possible directions of cleavage.

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.

	Figure 22-66. Druse of hetaerolite crystals from Franklin. This image is of part of the crystal shown in figure 22-65. Field of view is 0.2 mm in maximum dimension.

The writer 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. Such exsolved hetaerolite has [001] parallel to [0001] of zincite, as evidenced by optical examination. 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).

Composition

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 the writer, 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.

Occurrence and paragenesis

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 (Figure 22-50).

	Figure 22-67. Hetaerolite crystals from Sterling Hill. Field of view is 0.2 mm in maximum dimension. Photograph courtesy of Tom Peters and the Paterson Museum.		Figure 22-68. Fine-grained hetaerolite occurring as a pseudomorph after unknown precursor crystals from Franklin. Field of view is 0.4 mm in maximum dimension.

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 (Figures 22-66 and 22-67). It is quite likely that much hetaerolite has gone unrecognized, mislabeled as franklinite in Fe-poor secondary assemblages.

Name

Hetaerolite was named using the Greek word for “companion,” in reference to its close association with chalcophanite.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 11, 2001