BORNITE


Cu5FeS4,
copper iron sulfide




Bornite has been found at both Franklin and Sterling Hill, though in minor amounts, and rarely in some of the area marble quarries.  It was first identified from Franklin in 1928, in a specimen analyzed by Lawson Bauer, chief chemist for the New Jersey Zinc Company (Palache, 1928).  The specimen consisted of bornite intimately mixed with sphalerite, but the analysis, after deducting the components both known and believed to be present in the sphalerite, conformed almost perfectly to the composition of bornite.  Its presence at Franklin was later verified by Frondel (1972), who reported it also from Sterling Hill and remarked that numerous specimens had been found since Palache’s time.  Bornite at both localities occurs in massive granular form, commonly mixed with other sulfide minerals such as sphalerite (as in the original occurrence, described by Palache), chalcopyrite, and galena.

Bornite tarnishes readily, and hardly ever is its true color (reddish to bronzy brown) observed in natural specimens except upon a fresh break.  Iridescent colors of blue through purple are common in tarnished massive material, lending to bornite the common appellation of “peacock ore.”  It should be noted that other sulfide minerals, including chalcocite (common locally), chalcopyrite, pyrite, galena, and others, can develop similar iridescent tarnishes, resulting in more specimens labeled bornite in area collections than actually exist.  Iridescent franklinite, too, has commonly been mistaken for bornite, and to complicate matters, the term “peacock ore” in local parlance almost always refers to tarnished franklinite rather than bornite (Dunn, 1995, p. 530).  True bornite can be identified by a hardness test (to distinguish it from the much harder franklinite) and by its color upon a fresh break, which will serve to distinguish it from chalcocite (black), pyrite (brass yellow) chalcopyrite (golden yellow), and galena (dark gray), all of which lack the reddish cast of fresh bornite.  Galena also shows perfect cubic cleavage, so is readily identified even in highly tarnished masses. A positive flame test for copper is also helpful to distinguish bornite from some of the other local sulfides, though at least five other copper-bearing sulfides are known locally and commonly occur with bornite.

Bornite has not been much discussed in the local literature, and details of most occurrences are few or nonexistent.  A welcome exception is the paper by Jenkins and Misiur (1994), in which the geologic setting and genesis of a complicated veinlet assemblage of sulfide minerals and their oxidation products were documented in detail.  The sulfide assemblage occurred in marble near its contact with ore.

References

Cook, E. P., Fisher, K., Mutschler, F., and Navratil, G. (1958), The Buckwheat and Parker Dump minerals, Franklin, N.J. Franklin Mineral Digest, vol. 1, p. 27-30. [Describes bornite as “quite common” on the Buckwheat and Parker dumps, but generally in small grains and disseminations rather than large masses. Lists a number of assemblages]

Dunn, P.J. (1995), Franklin and Sterling Hill, New Jersey:  The world’s most magnificent mineral deposits. Privately published, 755 pp. [Description of bornite on p. 530]

Frondel, C. (1972), The minerals of Franklin and Sterling Hill - a checklist. Wiley Interscience, New York, 94 pp. [Verifies presence of bornite at Franklin and mentions recovery of numerous specimens since Palache’s first mention in 1928; also mentions its presence at Sterling Hill]

Jenkins, R.E., II and Misiur, S.C. (1994), A complex base-metal assemblage from the Sterling Mine, New Jersey. The Picking Table, vol. 35, no. 2, p. 19-24. [Detailed description of the mineralogy, paragenesis, and origin of sulfide minerals and their alteration products in a Cu-Pb-Zn veinlet assemblage below 700 level in the Sterling mine]

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 three bornite specimens shown on p. 796]

Palache, C. (1928), Mineralogical notes on Franklin and Sterling Hill, New Jersey. American Mineralogist, vol. 13, no. 7, p. 297-329. [First mention of bornite from Franklin; identification based on chemical analysis of impure material]

Palache, Charles. (1935), The minerals of Franklin and Sterling Hill, Sussex County, New Jersey. U.S. Geological Survey Professional Paper 180, 135 pp. [Provides on p. 29 the same information as in his 1928 paper]



Images




Massive, dark blue to violet bornite, golden-yellow chalcopyrite, franklinite-willemite-calcite ore, Franklin mine, Franklin NJ
Richard Schnurr (Fox Tail Images)
Massive, dark blue to violet (tarnished) bornite with golden-yellow chalcopyrite on altered, franklinite-willemite-calcite ore from Franklin. Embedded within the bornite mass in several areas are small masses of a dark greenish-brown mineral in divergent sprays of nearly fibrous crystals. Probably this is aegirine; see Dunn (1995, p. 431). Both the willemite and the calcite within 2 cm or so of the bornite mass are nonfluorescent, but the base of the specimen preserves a bit of less-altered ore showing the normal bright yellow-green SW fluorescence of the willemite. The specimen is from the collection of John Quick Stevens, former mine captain at Franklin, and a collector of its minerals from about 1910 to about 1945. The Stevens collection eventually was acquired by Richard Hauck, then of Bloomfield, NJ, and in April 1985 was purchased by Earl R. Verbeek (his specimen ERV-245). Subsequently it was donated to the Franklin Mineral Museum and became their specimen FMM-2743.

Identifier: BRN7a
Locality: Franklin mine, Franklin
Specimen size: 13 x 9 x 6.5 cm





Massive bornite, minor chalcopyrite, franklinite-willemite-calcite ore, Franklin mine, Franklin NJ
Richard Schnurr (Fox Tail Images)
Massive bornite with minor chalcopyrite on altered, franklinite-willemite-calcite ore from Franklin. The bornite shows the iridescent, blue to violet tarnish characteristic of the species. Most of the willemite in the ore is brown and appears serpentinized, but nevertheless retains its bright yellowish-green fluorescence SW. Near the bornite mass, in contrast, the willemite is bleached and nonfluorescent. Along one end of this specimen is a small and inconspicuous mass (5-6 mm across) of an unidentified mineral in dark brown, fibrous crystals embedded in the bornite. This may be aegirine; see the mention in Dunn (1995, p. 431). If so, the specimen is probably from the same find as BRN7. Incidentally, a typewritten note by Frank Edwards claims this mass of bornite was the “largest raised.” While perhaps true at one time, larger masses are now known to exist.
This specimen can be traced back to the collection of Billy Ball, a NJ Zinc Company employee who for years worked on the picking table at Franklin. The Ball collection was later dispersed by Schortmann's Minerals (Easthampton, Massachusetts). From there it entered the collection of Frank Edwards (longtime editor of The Picking Table) and eventually became part of the Lee Areson collection. In 1989 the Areson collection was purchased by Richard Hauck, from whom Earl R. Verbeek purchased this specimen, gave it catalog number ERV-501, and in May 2022 donated it to the Franklin Mineral Museum, where it remains as their specimen FMM-2742.

Identifier: BRN8a
Locality: Franklin mine, Franklin
Specimen size: 10 x 7 x 4 cm





Massive, fine-grained bornite, dark blue to violet, golden-yellow chalcopyrite, pale gray calcite, Franklin mine, Franklin NJ
Earl R. Verbeek
Massive, fine-grained bornite, tarnished dark blue to violet, with anhedral masses of coarse-grained, golden-yellow chalcopyrite and a little pale gray calcite. This is an old specimen with a tiny, discolored, and nearly illegible label glued to its base. The original owner is unknown, but subsequent owners include Lee Areson (LA 284) and Pete J. Dunn (Z-790). The Franklin Mineral Museum acquired this specimen in September 2010 upon its purchase of the bulk of the Dunn collection.

Identifier: BRN1a
Locality: Franklin mine, Franklin
Specimen size: 5.5 x 5 x 3 cm





Tarnished bornite, sphalerite and chalcopyrite, granular tephroite, calcite, Sterling mine, Ogdensburg, NJ
Earl R. Verbeek
The front of this specimen as photographed shows a large and rich mass of bornite with characteristic tarnish, associated with minor sphalerite and chalcopyrite. The sulfide mass is in contact with granular tephroite(?) and subordinate sphalerite in a matrix of red-fluorescent calcite. The specimen was collected in August 1979 by miner John Kolic and was no. 279 in his extensive collection, the whole of which was purchased in December 2013 by the Sterling Hill Mining Museum.

Identifier: BRN2a
Locality: 1620 Pillar, 1680 level, Sterling mine, Ogdensburg, NJ
Specimen size: 12 x 11.5 x 4.5 cm





Dark violet blebs of bornite, gold chalcopyrite, white calcite, dark green to brownish-green pyroxene, Sterling mine, Ogdensburg NJ
Earl R. Verbeek
Anhedral blebs of bornite (with dark violet tarnish) and gold-colored chalcopyrite (toward lower right of specimen) in a matrix of dull-red-fluorescing, medium-grained white calcite and a dark green to brownish-green pyroxene. The photographed face of the specimen is parallel to compositional layering in the matrix rock. The greatest concentration of bornite and chalcopyrite is in the "front" layer, 1.5-2.0 cm thick as exposed. A 3x5 card with this specimen shows that it was obtained in 1983 by an unnamed collector from Ed Stoll. Subsequently it entered the collection of Steven Phillips.

Identifier: BRN3a
Locality: Sterling mine, Ogdensburg
Specimen size: 12 x 12 x 7.5 cm





Bornite and chalcopyrite rimmed by magnetite and hematite, Sterling mine, Ogdensburg NJ
Emily Snyder
A sulfide “pod,” 4 cm in diameter, consisting mostly of bornite and chalcopyrite rimmed by magnetite and hematite. The surface of the pod has been sawn and polished to better show the textural relations among the sulfide minerals. The matrix rock is dark grayish green to almost black and is an altered, apparently chloritic gneiss, schistose in part. This is specimen GS225 of Stephen Sanford and is part of the extensive “geologic series” of his collection.

Identifier: BRN4a
Locality: Sterling mine, Ogdensburg
Specimen size: 15 x 9.5 x 4.5 cm



Bornite and chalcopyrite rimmed by magnetite and hematite, Sterling mine, Ogdensburg NJ
Emily Snyder
A close-up view of the bornite “pod” shown in the photograph above. The complex textural relations among minerals in such sulfide-rich masses from Sterling Hill and Franklin have been little studied, and much remains to be learned.

Identifier: BRN4c
Locality: Sterling mine, Ogdensburg
Specimen size: 15 x 9.5 x 4.5 cm





Blue bornite, brown sphalerite, calcite-rich matrix rock, Sterling mine, Ogdensburg NJ
Richard Schnurr (Fox Tail Images)
A large, anhedral mass of mixed sulfides, dominated by blue (tarnished) bornite and brown, nonfluorescent sphalerite, in contact with a calcite-rich matrix rock containing grains of fluorescent sphalerite (fluorescent orange, pink, and blue LW), bornite, franklinite, and traces of chalcopyrite or pyrite. The presence of both nonfluorescent, somewhat ferroan sphalerite and fluorescent, nearly iron-free sphalerite in different parts of the same specimen is intriguing. The sulfide mass contains numerous small bits of calcite, many 3-6 mm long and crudely oriented in parallel. This is specimen FMM-2761 of the Franklin Mineral Museum and was purchased from collector Doug Wahl in September 2021.

Identifier: BRN5a
Locality: Sterling mine, Ogdensburg
Specimen size: 14.5 x 10.5 x 8 cm





Bornite (tarnished blue) and arsenopyrite
Earl R. Verbeek
A handsome specimen of bornite (tarnished blue) and arsenopyrite from Sterling Hill. This specimen is exceptional both for the richness and relatively coarse grain size of its minerals. Formerly in the Rev. Thomas Fitzpatrick collection, it later became specimen 403 in the collection of John Kolic and presently is specimen SHMM-2291 of the Sterling Hill Mining Museum, which acquired it in December 2013 upon their purchase of the Kolic collection.

Identifier: BRN6a
Locality: 1340 crosscut, 1300 level, Sterling mine, Ogdensburg
Specimen size: 8 x 7.5 x 2.5 cm





Bornite concentrated in the upper right quadrant
Earl R. Verbeek
The bornite in this specimen is concentrated in the upper right quadrant as photographed. This specimen, though not as rich in bornite as some others pictured here, is notable for two reasons. One is that it comes from a precisely known locality in the Sterling mine, and the other is that this is one of the relatively few area specimens that contains gold visible to the naked eye. Though perhaps not obvious upon casual inspection, a flake of gold is present about one-quarter of the way in from the left edge of the specimen, a short distance below the centerline. Can you see it? This specimen was found by miner John Kolic in August 1979 and became no. 432 in his collection. It is now specimen SHMM-2268 of the Sterling Hill Mining Museum.

Identifier: BRN9a
Locality: 1620 undercut pillar, 1680 level, Sterling mine, Ogdensburg
Specimen size: 8 x 5.5 x 3 cm