Pyrrhotite, an iron sulfide mineral, is brassy yellow, opaque, and has metallic luster. It is found in small "hexagonal" crystals in the Franklin Marble, but most specimens consist of irregular grains, aggregates, or rounded, finger-like crystals or aggregates up to 5 cm in length by 1-2 cm wide, on which some planar features are present but commonly not definable as crystal faces. Massive pyrrhotite may display a lamellar or foliate texture.
Surficial alteration produces uncommonly an iridescent tarnish, not unlike that found on some chalcopyrite, but uneven. No full chemical analyses exist, but Palache (1935) reported the absence of cobalt and but a trace of nickel.
Pyrrhotite was described from the Franklin Marble by Palache (1935); the date of original recognition is obscure. It is known from Franklin, Sterling Hill, and the Franklin Marble, and may occur in the magnetite deposits as well. Davis (1993) provided isotopic data.
The preponderance of local pyrrhotite is found in the Franklin Marble, associated always with calcite, commonly with graphite, fluorite, pargasite, pyrite, arsenopyrite, and scapolite, and occasionally with chondrodite, titanite, and uvite (Palache, 1935).
Occurrences within the Franklin Mine are sparse; it has been found with amphibole and calcite in the Hamburg Mine, now part of the Franklin Mine. Pyrrhotite also occurs as 3 mm blebs in magnetite inclusions in the black-willemite occurrence at Franklin. At Sterling Hill it has been found associated with amphibole and pyroxene and always with calcite. (Dunn, 1995)

 Location Found: Franklin and Ogdensburg
 Formula: Fe7S8
 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   Pyrrhotite

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.538

Frondel, Clifford (1972). The minerals of Franklin and Sterling Hill, a checklist. NY.: John Willey & Sons. p.72

The Picking Table References
 PT Issue and PageDescription / Comment
View IssueV. 27 No. 2 - Fall 1986, pg. 7Minerals of the Franklin Quarry, Philip P. Betancourt, Pyrrhotite
View IssueV. 7, No. 2 - August 1966, pg. 12The Minerals of Sterling Hill 1962-65 by Frank Z. Edwards - Pyrrhotite (small article)
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