Nickeline is a nickel arsenide mineral. The analyses by Oen et al. (1984) show it to be fairly constant in composition and slightly antimonian.
Nickeline, also called niccolite, occurred in an isolated, anomalous assemblage in the Trotter Shaft at Franklin. It was a rare occurrence, apparently very limited in extent, and has not been found elsewhere in the mine, nor at Sterling Hill. Relations to the ore are unknown. Franklin nickeline is associated with rammelsbergite, pararammelsbergite, safflorite, loellingite, gersdorffite, arsenopyrite, and other species described herein, but the overall assemblage description and history is given here but once.
The nickeline assemblage was first reported by Koenig (1889, 1890), who had observed some 30 pounds of material. He reported only small grains of nickeline and gave a longer description of the white nickel arsenides, which he referred to as chloanthite and which he said formed the bulk of the material observed. These white arsenides were later shown to be other arsenide species listed here. Although Palache (1935) reported hearsay of several hundred pounds of material, the bulk of which was found after Koenig's description, relatively little specimen material is known today. This might have been incorrect or large amounts may have been lost or consumed in chemical experiments. Crude crystals were reported by Palache (1935) to occur where nickeline is in contact with calcite or fluorite. The assemblage was subsequently studied by Holmes (1935, 1936, 1945, 1947), who established the absence of chloanthite and the presence of rammelsbergite, pararammelsbergite, and skutterudite.
The definitive chemical and textural study was performed by Oen et al. (1984), who described the assemblage in great detail, added loellingite and safflorite as associated minerals, and provided a detailed model for the crystallization sequence and phase equilibria. This assemblage hosts the Fe-, Ni-, and Co-bearing members of the loellingite group, which are loellingite, rammelsbergite, and safflorite, respectively. Breithauptite was added by Verbeek and Sutphin (1990).
Nickeline is light orange-pink, opaque, and has metallic luster and no cleavage. It commonly occurs as bleb-like grains and massive aggregates and as dendrites, some of which serve as the core nucleus for dendrites of the white arsenides. It is not confused with other local minerals, except freshly-broken bornite, which is always associated with sulfides and tarnishes readily.
Franklin nickeline occurs as dendrites in a matrix of sphalerite, fluorite, calcite, and barite. Koenig (1890) noted that it occurred at a depth of 340 feet within an abundance of sphalerite and fluorite, under a layer of yellow andradite.
The nickeline assemblage is one of dendritic growth. The dendrites are about 7-8 cm in length, several mm thick at their bases, and have trunks rimmed with white arsenides.
Toward their ends, the trunks become more arborescent and rimmed with enlarged, cm-wide, rounded, cauliflower-like, concentric aggregates of gersdorffite and rammelsbergite. Some nickeline dendrites exhibit very little, if any, replacement by the white arsenides (rammelsbergite and pararammelsbergite) or gersdorffite; these simpler dendrites are narrower. Calcite interstitial to the dendrites is recrystallized.
In the general case, nickeline is the first formed of these minerals and is followed in the sequence of crystallization by rammelsbergite and pararammelsbergite, and then by gersdorffite and loellingite, and lastly, but only locally, by the rarer minerals skutterudite and safflorite. Magnetite occurs sporadically in calcite near the ends of some dendrites. The outward growth of the dendrites is accompanied by depletion of nickel and enrichment of cobalt.
The gangue is commonly calcite, sphalerite, fluorite, barite, and rarely ferrostilpnomelane. Some fluorite is colored violet in contact with arsenides. Subsequent alterations have produced minor amounts of pimelite and annabergite. Few specimens have vugs; where present they enclose 5-7 mm crystals of fluorite and, in one case, superb nickeline crystals, which are in the Hancock Collection at Harvard University.
Some extant dendritic specimens show only minor residual nickeline, with relatively larger amounts of the white arsenides and gersdorffite, in keeping with Koenig's original description of relative abundance, but others are almost wholly nickeline. Koenig did not mention dendrites, but they are commonly not apparent until the assemblage is sliced into slabs. Considering the statements of Koenig and Palache, it is very surprising that only a small number of specimens are known or could be located by [Dunn]. [Dunn’s] dissolution of some calcite matrix in search of other associated species found insoluble residues of rutile, chlorite, and pararammelsbergite. (Dunn, 1995)

 Location Found: Franklin
 Mineral Note: Niccolite is an alternate name
 Formula: NiAs
 Essential Elements: Arsenic, Nickel
 All Elements in Formula: Arsenic, Nickel
 IMA Status: Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
 To find out more about this mineral at minDat's website, follow this link   Nickeline

Dunn, Pete J. (1995). Franklin and Sterling Hill New Jersey: the world's most magnificent mineral deposits. Franklin, NJ.: The Franklin-Ogdensburg Mineralogical Society. p.547

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.69

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 31, No. 1 - Spring 1990, pg. 3Breithauptite From The Nickel-Arsenide Assemblage at Franklin, New Jersey, Nickeline (small description)

Nickeline, pimelite, fluorite and sphalerite from Franklin, NJ
Nickeline (golden copper metallic), pimelite (green), fluorite (purple) and sphalerite (yellow to brown) from Franklin, NJ. Field of view 1" x 3/4". From the collection of, and photo by Robert A. Boymistruk.

Sawn nickeline, fluorite, calcite and minor rammelsbergite from Franklin, NJ
Sawn nickeline (brass-colored), fluorite (violet), calcite (white to light gray) and minor rammelsbergite (silver-colored) from Franklin New Jersey. The insert shows a natural edge of the nickeline. 1.5" x 1". From the collection of Zack and Ralph Bonard, photo by WP.

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