MAGNUSSONITE


Mn10As6O18(OH,Cl)2,
manganese arsenite hydroxide




Sterling Hill is the second world locality for magnussonite, a mineral originally described from Långban, Sweden, by Gabrielson (1956). A specimen of magnussonite from Sterling Hill, now in the collection of Harvard University (HU-95036), had been found and analyzed more than two decades before, but was not then described as a new species. In 1961, however, Clifford Frondel, professor of mineralogy at Harvard, recognized the Harvard specimen for what is was, adding one more mineral to the local species list (Frondel, 1961). That original specimen was quite lean in magnussonite, but two of the later finds at Sterling Hill produced far richer material. Sterling Hill remains the premiere world locality for the species, which even today is known from few localities on the planet.

Beyond the original Harvard specimen, magnussonite was found again at Sterling Hill in 1980 (Sanford, 1983), in cross-member ore near the 800 level. Despite specimens having been found “in some abundance,” the magnussonite was present only in small (about 0.5 mm), visually inconspicuous grains.  The later 1983 and especially the 1989 finds, in 1020 stope near 1200 level, far eclipsed the earlier ones and furnished veins of glassy, dark green to brown magnussonite 9-12 mm thick (Kolic and Sanford, 1993). The locality for the 1989 find was given by Kolic and Sanford as 30 ft above 1200 level, at mine coordinates 1075N, 750W. The magnussonite in this area occurred along a lengthy, gently sinuous fault of orientation N69W/32NE, along which the upper plate had moved west-northwest (Verbeek and Grout, 2025). This was the largest fault in that area, traceable through both ribs and across the back, and offset the footwall contact of ore about 1.5 m. Members of this set of faults throughout the Sterling mine commonly consist of multiple strands that split and merge along their length. Movement along such nonplanar faults resulted in the opening of lenticular voids, which upon mineralization became irregular veins (e.g., MGN3). Subsidiary shears visible on the hand-specimen scale are likewise common (MGN2, MGN3).

Magnussonite is a hydrothermal vein mineral at Sterling Hill and almost invariably occurs with zincite in the same veins. Additional associated minerals include copper and alleghanyite (800 level occurrence; Dunn, 1995), and mcgovernite (1200 level occurrence; MGN4).

References

Dunn, P.J. (1995), Franklin and Sterling Hill, New Jersey:  the world’s most magnificent mineral deposits. Privately published in five volumes, 755 pp. [Description of magnussonite on p. 672]

Dunn, P.J. and Ramik, R.A. (1984), Magnussonite: new chemical data, an occurrence at Sterling Hill, New Jersey, and new data on a related phase from the Brattfors mine, Sweden. American Mineralogist, vol. 69, p. 800-802.
 
Edwards, F.Z. (1977), The post-Palache minerals. The Picking Table, vol. 18, no. 1, p. 9-14. [Discussion of magnussonite on p. 11-12; only one specimen from Sterling Hill then known]

Frondel, Clifford (1961), Magnussonite from Sterling Hill, New Jersey. Arkiv för Mineralogi och Geologi Stockholm, vol. 2, p. 571.

Gabrielson, O. (1956), Magnussonite, a new arsenite mineral from the Långban mine, Sweden. Arkiv för Mineralogi och Geologi, vol. 2, p. 133-135 [First description of the species]

King, V.T., King, N.E., Betancourt, P.P., Bostwick, R.C., Chin, Peter, Hecht, T.J., Kuitems, S.M., Moritz, H., Nemetz, J.D., Nikischer, A.J., Sanford, S., Van Fleet, J.A., and Verbeek, E.R. (2021), The Mineralogy of Franklin and Ogdensburg, New Jersey—A Photographic Celebration. Privately published, 1400 pp. [Photos of magnussonite on p. 530 and 974]

Kolic, John and Sanford, Stephen (1993), Recent mineral finds from the Sterling mine, Ogdensburg, New Jersey. The Picking Table, vol. 34, no. 2, p. 12-21. [Mention of magnussonite from the 1983 and 1989 finds in 1020 stope near 1200 level on p. 13; gives mine coordinates]

Moore, P.B. (1970), Stenhuggarite, a new mineral from Långban and new data on magnussonite. Arkiv för Mineralogi och Geologi, vol. 5, p. 55-62. [Presents new crystallographic data on magnussonite at variance from data of the same species from the type locality]

Moore, P.B. (1971), Stenhuggarite, a new mineral from Långban and new data on magnussonite. American Mineralogist, vol. 56, nos. 3-4, p. 639. [A one-paragraph extract, by Adolph Pabst, of data on magnussonite from the 1970 paper by Moore given above]

Sanford, Stephen (1983), Recent mineral occurrences at Sterling Hill. The Picking Table, vol. 24, no. 1, p. 3-6. [Mention of a 1980 find of magnussonite from near 800 level on p. 6]

Verbeek, E.R. and Grout, M.A., 2025, Fault History of the Sterling Zinc Mine, Ogdensburg, Sussex County, New Jersey, with Appendices, in Di Maio, M.P., Herman, G.C., and Verbeek, E.R. (eds.), Revisiting the Sterling Hill Orebody: Challenges in Understanding and Mining this Magnificent Deposit: 41st Annual Proceedings and Field Guide of the Geological Association of New Jersey, The Sterling Hill Mining Museum, Ogdensburg, NJ, p. 117-140. [Magnussonite at Sterling Hill was deposited along a Set 2 thrust fault as described in this paper. Details of this fault, no. 1155 of the Verbeek-Grout dataset, are given in Appendix A, and the Kolic find is described on p. 44 of Appendix C]



Images




Dark olive green to (locally) dark brown magnussonite and orange-red zincite
Earl R. Verbeek
Dark olive green to (locally) dark brown magnussonite and orange-red zincite in an irregular vein ranging in thickness from near-zero to 1.2 cm, in faulted and slightly brecciated, granular willemite-franklinite-calcite ore. Note the irregular, subsidiary shears both above and below the main vein. This was specimen GG1911 in the collection of Gary Grenier, who purchased it in July 1995 from Robert Boymistruk. A paper label accompanying this piece suggests that Mr. Boymistruk had earlier purchased it from Ewald Gerstmann. The specimen is now (2024) owned by Steven Phillips.

Identifier: MGN3a
Locality: Sterling mine, Ogdensburg
Specimen size: 11 x 8 x 4 cm





Assemblage of glassy, dark brown magnussonite with bright orange-red zincite
Earl R. Verbeek
A specimen split along the vein to reveal an attractive assemblage of glassy, dark brown magnussonite with bright orange-red zincite. The white mineral is calcite, and the micaceous, medium-brown mineral (abundant at lower left) is mcgovernite. The matrix rock, seen at far left, is granular willemite-franklinite-calcite ore. The preserved portion of the vein at its thickest is 2.1 cm. The reverse side of this specimen, especially rich in mcgovernite in crude radial groups of flattened crystals, is shown in photo MGN4b.
The history of this specimen is well known. It was collected by John Kolic and was specimen no. 496 in his collection. In 1996 Mr. Kolic offered it for auction by the Sterling Hill Mining Museum. The winning bidder was Gary Grenier, who assigned it catalogue number GG2831. It later passed to Steven Phillips upon his purchase of the Grenier collection.

Identifier: MGN4a
Locality: 1020 Stope, 10 ft below 1100 level, west limb, Sterling mine, Ogdensburg
Specimen size: 6 x 4 x 2 cm



Assemblage of glassy, dark brown magnussonite with bright orange-red zincite
Earl R. Verbeek
The reverse side of the magnussonite specimen MGN4a, showing intergrown, flattened, radial groups of mcgovernite crystals atop a film of calcite.

Identifier: MGN4b
Locality: 1020 Stope, 10 ft below 1100 level, west limb, Sterling mine, Ogdensburg
Specimen size: 6 x 4 x 2 cm





Dark olive-green to brown magnussonite, slightly brecciated, granular willemite-franklinite-calcite ore
Earl R. Verbeek
Dark olive-green to brown magnussonite, broken partly along the vein, in sheared and slightly brecciated, granular willemite-franklinite-calcite ore. Small, broken fragments of ore are present within the magnussonite; note also the subsidiary shear surface cutting diagonally through the ore. Minor secondary zincite, common in this assemblage, is present on the back of the specimen. The mineral dealer Fred Parker sold this specimen to Gary Grenier in January 1990; it was specimen GG 942 in the Grenier collection and later passed to Steven Phillips.

Identifier: MGN2a
Locality: 1020 stope, 1200 level, Sterling mine, Ogdensburg
Specimen size: 11.5 x 5.5 x 3.5 cm





Vein 2-7 mm thick of dark green to brown magnussonite cutting calcitic willemite-franklinite ore
Earl R. Verbeek
A front-on view of a vein 2-7 mm thick of dark green to brown magnussonite cutting calcitic willemite-franklinite ore from 1200 level of the Sterling mine. The dark olive-green color of fresh magnussonite is seen along the right edge of the vein. Note the slickenlines on the brown surface of the vein where it was in contact with the wall rock. This specimen was collected by miner John Kolic and later entered the Dave Wellbrock (M0974) and Mark Leger (ML314) collections. Mr. Leger’s collection catalog mentions that he purchased it from Mr. Wellbrock the first time he met him, in the basement of Dick Hauck’s home in Bloomfield, New Jersey, and further remarked on the long friendship between them.

Identifier: MGN6a
Locality: 1020 stope, 1200 level, Sterling mine, Ogdensburg
Specimen size: 12 x 6 x 5.5 cm





Dark brownish-green, somewhat glassy, massive magnussonite in altered, sheared, franklinite-willemite-calcite ore.
Earl R. Verbeek
Dark brownish-green, somewhat glassy, massive magnussonite as part of a vein assemblage in altered, sheared, franklinite-willemite-calcite ore. Blebs of deep red zincite are present within the magnussonite, and in places along the vein margin is a narrow zone containing flakes of reddish-brown mcgovernite (lower part of vein as photographed). This specimen was purchased by Mark Leger from Chet Lemanski in August 2018 and became no. ML315 in the Leger collection.

Identifier: MGN7a
Locality: 1020 stope, 1200 level, Sterling mine, Ogdensburg
Specimen size: 9 x 3.5 x 2.5 cm