HAUSMANNITE

Mn²⁺Mn³⁺₂O₄ 
Tetragonal

	Figure 22-61. Subparallel array of acicular hausmannite crystals from Franklin. Field of view is 2 mm in maximum dimension.

Hausmannite was reported by Frondel (1972) to have been known from Franklin and Sterling Hill by Palache and Bauer, respectively, early in the century, but not described. An occurrence with manganosite was described by McSween (1976). It is a rare mineral locally.

Description

Hausmannite occurs as massive fine-grained material, equant {111} crystals, and subparallel fascicles of acicular 2-3 mm crystals (Figure 22-61). Its color varies from predominantly black to rarely reddish-brown. No physical or optical measurements have been made. Much of this material is microscopic. 

Composition

Hausmannite is a manganese oxide mineral. Few analytical data exist. McSween found the hausmannite associated with manganosite to have SiO₂ 0.3, Al₂O₃ 0.51, FeO 5.85, MgO 0.16, MnO 11.53, Mn₂O₃ 69.01, ZnO 12.91, total = 100.00 wt. %. This material has Zn:Mn²⁺ nearly 1:1 and is thus intermediate in composition between hausmannite and hetaerolite. The acicular crystals from the groutite assemblage (Figure 22-61) have SiO₂ 0.3, Fe₂O₃ 0.4, MgO 0.4, ZnO 0.8, MnO 29.2, Mn₂O₃ 69.8, total = 100.9 wt. %, with Mn²⁺ assumed and calculated according to the known stoichiometry of hausmannite. Additional specimens from this assemblage were observed by the writer which, although not chemically analyzed, yielded X-ray patterns much closer to that of hausmannite than that of hetaerolite.

Occurrence and paragenesis

Hausmannite is not a common mineral locally, unlike its occurrence as a dominant oxide at Långban, Sweden. Occurrences are few and minor, but many occurrences may exist unrecognized.

Hausmannite occurs as thin rims of fine-grained material which separates zincite from manganosite in some specimens of the Franklin zincite-manganosite exsolution assemblage. Its relative abundance in this assemblage has not been studied.

Hausmannite is also known as reddish brown, stiff, prismatic crystals, arranged in subparallel slightly divergent aggregates, within the groutite and brown andradite assemblage described herein (Figure 22-61). In this assemblage, it can be associated with groutite, cahnite, calcite, and kentrolite (Dunn, 1987). It has also been found as 0.5 mm prismatic crystals with flinkite and jarosewichite.

Hausmannite rarely occurs as superb, euhedral crystals of pseudo-octahedral habit in solution vugs in willemite and may occur unrecognized in other associations as well, especially in Zn-poor assemblages; in the presence of Zn, hetaerolite is more common.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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