PYRRHOTITE

Fe_1-xS
Monoclinic and Hexagonal

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.

Description

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.

Occurrence and paragenesis

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.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 11, 2001