Pyrite is an iron sulfide mineral. There are few analyses of local material; that of Kraus and Scott (1907) reported 1.25 wt. % Co.
Pyrite was first reported from Franklin by Vanuxem and Keating (1822b) and later by Kraus and Scott (1907) and Palache (1935, 1941b). It was observed at Sterling Hill by Kemp (1893). Pyrite likely occurs in sulfide segregations in the magnetite deposits as well.
Pyrite from the Franklin Marble occurs as euhedral, equant crystals of great morphological diversity, as shown by Palache (1935). The crystals, to several cm in diameter, occur isolated in the marble, are dominantly cubic in habit, and many are highly modified by the octahedron, pyritohedron, and trapezohedron; each of these forms also occur as the dominant form on crystals. Diverse habits for pyrite occur in the Buckwheat Dolomite (Peters et al., 1983). Pyrite also occurs as massive material in veins. It is brassy yellow, metallic in luster, with no cleavage. It is differentiated from other similar sulfides by its color, superior hardness, and morphology. Some euhedral crystals are metastable and may decompose on exposure; the process, with respect to local material, is a relatively sluggish one, sometimes taking a half-century or more in institutional collections.
Pyrite occurs in isolated crystals and as massive material in the Franklin Marble, associated with uvite, graphite, amphiboles, arsenopyrite, tremolite, and other minerals. It was noted from the Fowler Quarry (Palache, 1935). The Kittatinny Limestone and Buckwheat Dolomite are hosts to pyrite, and it occurs within the magnetite deposits on Balls Hill.
Within the orebodies, it is more abundant at Sterling Hill than at Franklin and occurs with hematite and dolomite in the north orebody. Although not directly associated with the ores, it is common in the younger sulfide veins. Such veins may be massive and many cm thick. Pyrite is intimately associated with sphalerite, calcite, galena, magnetite, chalcopyrite, and other species at both Franklin and Sterling Hill. Ries and Bowen (1922) reported pyrite in breccias and fractures at Franklin, but in greatest quantity as contact rims, 60 cm wide in some cases, where it borders intrusive pegmatite. One of the finer Franklin occurrences is of crystals with fluorapophyllite and hedenbergite in the footwall Cork Hill Gneiss. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: FeS2
 Essential Elements: Iron, Sulfur
 All Elements in Formula: Iron, Sulfur
 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   Pyrite

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.535

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.71

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 30, No. 1 - Spring 1989, pg. 9The Epidote-Pyroxene-Fluorapophyllite Assemblage in the Franklin Mine at Franklin, New Jersey, Philip P. Betancourt, Pyrite (small description)
View IssueV. 27 No. 2 - Fall 1986, pg. 7Minerals of the Franklin Quarry, Philip P. Betancourt, Pyrite
View IssueV. 24 No. 2 - Fall 1983, pg. 15Minerals of the Buckwheat Dolomite Franklin, New Jersey, Pyrite (small description)
View IssueV. 11, No. 2 - August 1970, pg. 10Additional Mineral Notes - Pyrite (small article)
View IssueV. 7, No. 2 - August 1966, pg. 12The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Pyrite (small article)

Pyrite crystals on dolomite matrix, Franklin, NJ.
Pyrite crystals on dolomite matrix, Franklin, NJ. Photo by JVF.

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