AZURITE

Cu₃(CO₃)₂(OH)₂,
copper carbonate hydroxide

Azurite is a product of weathering at both Franklin and Sterling Hill, where it occurs chiefly as small anhedral masses, but also as tiny crystals in vugs and thin films on fracture surfaces.  Until recently it was regarded as a rare (Palache, 1935, p. 57) to uncommon (Dunn, 1995, p. 619) mineral locally.  Frondel (1972, p. 44) commented that it was known chiefly in micromounts, but hand-sized specimens were collected in abundance during the latter stages of production in the Sterling mine, and a surface find at Sterling Hill during the early 2000s added dozens more.  The recent finds notwithstanding, most specimens of azurite are lean in that mineral, and good specimens remain uncommon.  It should also be noted that a “good” specimen of azurite in local terms pales in comparison to even modest specimens from dozens of other localities worldwide.  Nonetheless, fine crystals of azurite, rich in crystal forms, have been recovered from both Franklin and Sterling Hill, these comparing in quality to some of the world’s best in everything but size.  Though few exceed 5 mm in maximum dimension, they are highly prized among collectors of the local minerals and were extensively figured by Palache (1935, p. 58).

The first mention of local azurite in print is that of Vanuxem and Keating (1822), but surface showings of secondary copper minerals, azurite included, had probably been noticed far earlier, perhaps by Dutch explorers in the 1600s, or by the original inhabitants, the Lenni Lenape.  The rich blue color of azurite would certainly have stood out against the generally brown to gray color of weathered Franklin Marble, and it often occurs with malachite, an equally conspicuous mineral, and a more abundant one.  Of these possible early findings, however, the historical record is silent.

Notable finds of azurite in the Franklin-Ogdensburg area are few but are listed here in brief:
    • The informally named “copper zone” peripheral to the northern part of the Passaic pit and underlying mud zone was the source of many specimens from the upper levels of the Sterling mine during the 1970s.  Most of the azurite specimens in collections of the local minerals came from this area.
    • Secondary copper minerals were collected in 2007 by Robert Hauck from a surface exposure of the Franklin Marble in the high, rugged ground just south of the southern margin of the Passaic pit.  In this area azurite occurred with malachite and remnant chalcopyrite. Several spackle buckets of specimens were recovered; the best examples are in the collection of the Sterling Hill Mining Museum.  Coordinates:
    UTM:  18T, 4547940N, 0533051E, +/- 20 ft (WGS84)
    Lat/Long:  41^o04’55.38” North, 74^o36’23.47” West
    • Azurite in the Franklin mine was found along the northern part of the west limb of ore, in the shallow mine workings beneath the Hardyston unconformity.  This part of the Franklin deposit had been exposed during late Neoproterozoic time and had developed a gossan cap due to extensive weathering. The azurite occurs with malachite and aurichalcite on a limonitic matrix.  Specimens are uncommon because this part of the mine was unstable and was off-limits for most personnel.  Palache (1928, p. 297) gave the locality for specimens from the Stanton collection as 720 pillar on 200 level.
    • In addition to these occurrences, azurite has been found, albeit rarely, in some of the area marble quarries.  Betancourt (1986) documented one such find from the northern part of the Franklin Braen quarry, where azurite occurred as thin films, small masses, and tiny crystals in fractures through the marble.

References

Betancourt, P.P. (1986), Minerals of the Franklin quarry.  The Picking Table, vol. 27, no. 2, p. 2-10.  [Short description on p. 5 of a 1984 find of azurite in one of the local marble quarries]

Dunn, P.J. (1995), Franklin and Sterling Hill, New Jersey:  the world’s most magnificent mineral deposits.  Privately published, 755 p.  [Describes azurite on p. 618-619; suggests that some azurite may have formed by alteration of parent chalcocite-magnetite intergrowths]

Edwards, F.Z. (1966), The minerals of Sterling Hill, 1962-65.  The Picking Table, vol. 7, no. 2, p. 3-15.  [Describes, on p. 6, azurite as small blebs and microcrystals from the Sterling mine]

Frondel, Clifford (1972), The minerals of Franklin and Sterling Hill - a check list.  Wiley-Interscience, 94 p.  [Brief description of azurite on p. 44; mentions that few good specimens were known at the time]

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 azurite specimens, mostly microcrystals, on p. 786]

Palache, C., 1928, Mineralogical notes on Franklin and Sterling Hill, New Jersey.  American Mineralogist, vol. 13, p. 297-329.  [First published description of azurite from the Franklin-Ogdensburg area; provides projections of azurite crystals and lists the forms present]

Palache, Charles (1935), The minerals of Franklin and Sterling Hill, Sussex County, New Jersey. U.S. Geological Survey Professional Paper 180, 135 pp. [Repeats much of the information from his 1928 paper, with some updates; see p. 57-58.  Emphasizes that azurite crystals from Franklin are rich in forms and provides a tabular summary and line illustrations of combinations of forms observed]

Vanuxem, L. and Keating, W.H. (1822), On the geology and mineralogy of Franklin, in Sussex County, New Jersey.  Academy of Natural Sciences of Philadelphia Journal, vol. 2, p. 277-288.  [Earliest published mention of azurite (as “blue carbonate of copper”) from the Franklin area.  List only; no data or description]

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