LEAD


Pb,
native lead




Lead at Franklin commonly occurs as tiny, finely dispersed platelets within grains of other minerals – willemite, feldspars, axinite-(Mn), grossular, roeblingite, etc. – to all of which it imparts a pale bluish gray to dark gray color, depending on abundance. In this form (e.g. LED1) the lead itself is generally not visible as such, though Dunn (1995, p. 523) notes that platelets in transparent minerals “commonly have a silvery appearance.”  Similarly, in granular aggregates, thin films of lead as grain coatings lend to the aggregate an overall gray color, as in some specimens of minehillite.

Macroscopically visible lead is most common as thin sheets and small, branching aggregates on relict cleavage surfaces in altered hendricksite (“caswellite”). Cleavage surfaces within such minerals as bustamite, rhodonite, and feldspar may similarly be filmed with lead and appear, in cross section, as short, parallel, dark lines or streaks. Lead also occurs as fracture fillings, some several centimeters or more in length, but hair thin. Only rarely does lead form masses, and even these are small, the largest known to us measuring only about 1.5 cm in length (see photo in King et al., 2021, p. 457).

Confirmed occurrences of lead to date are all from the orebody at Franklin, mostly from the “Parker Shaft suite” of altered calcium silicate minerals. Lead has been reported once from Sterling Hill (DiFrancesco et al., 2010) as micrograins in dark gray calcite marble, but analytical data to confirm the occurrence are lacking.

References

Burke, E.A.J. and Dunn, P.J. (1988), Cuprostibite, domeykite, native copper and native lead from the Franklin Mine, New Jersey, (USA). Neues Jahrbuch für Mineralogie Monatshefte (1988), p. 145-148.

DiFrancesco, N.J., Huska, A., Powell, W., and Verbeek, E.R. (2010), A high resolution geologic map of the Sterling Hill mine [abs.]. Geological Society of America Abstracts with Programs, vol. 42, no. 5, p. 99. [Brief mention of a dark gray marble unit containing microinclusions of lead in the “saddle area” between the Passaic and Noble pits at Sterling Hill]

Dunn, P.J. (1995), Franklin and Sterling Hill, New Jersey:  the world’s most magnificent mineral deposits. Privately published in five volumes, 755 pp. [Summarized the extant knowledge of native lead at Franklin on p. 522]

Foote, W.M. (1898), Note on the occurrence of native lead with roeblingite, native copper, and other minerals at Franklin Furnace, N.J. American Journal of Science, 4th series, vol. 6, p. 187-188. [First mention and description of native lead from Franklin]

Frondel, C. (1972), The minerals of Franklin and Sterling Hill - a checklist. Wiley Interscience, New York, 94 pp. [Brief but skilled description of native lead from Franklin on p. 64]

King, V.T., King, N.E., Betancourt, P.P., Bostwick, R.C., Chin, Peter, Hecht, T.J., Kuitems, S.M., Moritz, Harold, Nemetz, J.D., Nikischer, A.J., Sanford, Stephen, 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 lead on pp. 457, 956, and 957]

Palache, Charles (1935), The minerals of Franklin and Sterling Hill, Sussex County, New Jersey. U.S. Geological Survey Professional Paper 180, 135 pp. [One-paragraph description of lead from Franklin on p. 26]



Images




Dark gray disseminations of native lead in massive, fine-grained grossular
Earl R. Verbeek
Dark gray disseminations of native lead in massive, fine-grained grossular, mostly of pale pink color where free of lead, but locally greenish due to local concentrations of gahnite microcrystals. Additional minerals include pinkish “caswellite” and andradite (amber brown), mostly on lower right side of specimen, plus a little white, scaly prehnite at upper left. The gray pigmentation by lead is especially pronounced in this example, from the collection of Paul Shizume.

Identifier: LED1a
Locality: Franklin mine, Franklin
Specimen size: Photographed face is 10 x 6 cm





Native lead along the contact between an ivory-colored, perthitic feldspar, a mixture of pinkish-orange “caswellite” and andradite
Earl R. Verbeek
Native lead along the contact between an ivory-colored, perthitic feldspar (probably microcline) on the left and a mixture of pinkish-orange “caswellite” and andradite on the right. At lower right is a thin layer of fine-grained franklinite-willemite ore. Cleavage surfaces in the feldspar bear light, patchy coatings of margarosanite (fl. blue SW) and minor clinohedrite (fl. orange SW). As of 2011 this specimen was in the collection of Richard Keller, former managing editor of The Picking Table.

Identifier: LED2a
Locality: Franklin mine, Franklin
Specimen size: 11 x 9.5 x 6.5 cm



Native lead along the contact between an ivory-colored, perthitic feldspar, a mixture of pinkish-orange “caswellite” and andradite
Earl R. Verbeek
Close-up view of films and small scales of native lead (dark bluish-gray, with dull luster) on relict cleavage surfaces of “caswellite” (altered and replaced hendricksite mica) in the lower right portion of photo LED2a.

Field of view: The horizontal width is 3.3 cm.

Identifier: LED2c
Locality: Franklin mine, Franklin
Specimen size: 11 x 9.5 x 6.5 cm





Native lead in fine grains dispersed in pale pink grossular, pale yellow axinite-(Mn); minor amber-colored andradite, scattered grains of franklinite
Earl R. Verbeek
Native lead in fine grains dispersed in pale pink grossular, coloring it dark gray. Associated minerals include pale yellow axinite-(Mn); minor amber-colored andradite; a few small, scattered grains of franklinite; and (on base, not visible) a tiny grain of native copper. This fine example, formerly no. 8 in the collection of Sterling Hill miner John Kolic (1943-2014), was acquired in 2014 by the Sterling Hill Mining Museum and is now their specimen SHMM-2185.

Identifier: LED3a
Locality: Franklin mine, Franklin
Specimen size: 8.5 x 6 x 4.5 cm





Native lead in abundant, millimeter-size masses and grain coatings in a matrix of pink grossular, orange-tan axinite-(Mn),
Earl R. Verbeek
Native lead in abundant, millimeter-size masses and grain coatings in a matrix of pink grossular, orange-tan axinite-(Mn), and (especially on back and right side as photographed), ivory-colored to pale tan, massive willemite. This colorful specimen, unusually rich in lead, formerly belonged to Richard Hauck (his specimen no. 311) and is now in the collection of Steven Phillips of Hamburg, New Jersey.

Identifier: LED4a
Locality: Franklin mine, Franklin
Specimen size: 8.5 x 6 x 5 cm





Massive feldspar colored dark gray to bluish-gray by dispersed, microscopic grains of native lead
Earl R. Verbeek
Massive feldspar colored dark gray to bluish-gray by dispersed, microscopic grains of native lead. Embedded in the feldspar are grains of andradite, franklinite, and hendricksite (particularly on back), locally with a little willemite and calcite. An accompanying label identifies the feldspar as hyalophane, but the specimen appears insufficiently dense to support that claim, and it is probably microcline instead. This specimen has had at least four owners, three of whom are known: John E. MacDonald (JEM 48), Joe Cilen (14,648), and most recently, Steven Phillips.

Identifier: LED5a
Locality: Franklin mine, Franklin
Specimen size: 7 x 5.5 x 4 cm