PYRITE

FeS₂
Cubic

	Figure 21-12. Crystal drawings of pyrite from the Fowler Quarry in Franklin. Drawings are from Palache (1935) who provided crystallographic data.

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.

Description

Pyrite from the Franklin Marble occurs as euhedral, equant crystals of great morphological diversity, as shown by Palache (1935) (Figures  21-12 and 21-13).

	Figure  21-13. Crystal drawings of pyrite. The lower drawing is of coigns of a crystal from the Buckwheat Mine; the upper one is presumably from Franklin. Drawings are from Palache (1935) who provided crystallographic data.

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.

Composition

Pyrite is an iron sulfide mineral. There are few analyses of local material; that of Kraus and Scott (1907) reported 1.25 wt. % Co.

	Figure 21-14. Equant, sharp, euhedral pyrite crystals in the white calcite of the Franklin Marble from Franklin. Left specimen is 5 cm in maximum dimension and privately owned; right specimen is 6 cm in maximum dimension, Smithsonian Institution, #C615-2. Photos by the author.		Figure 21-15. Pyrite crystals from the Buckwheat Dolomite. Largest crystal is approximately 0.5 mm in maximum dimension. Photo courtesy of Tom Peters and the Paterson Museum.

Occurrence and paragenesis

Pyrite occurs in isolated crystals and as massive material in the Franklin Marble, associated with uvite, graphite, amphiboles, arsenopyrite, tremolite, and other minerals (Figures 21-14 and 21-17). It was noted from the Fowler Quarry (Palache, 1935). The Kittatinny Limestone and Buckwheat Dolomite are hosts to pyrite (Figures 21-15 and 21-16), and it occurs within the magnetite deposits on Balls Hill.

	Figure 21-16. Pyrite crystal from the Buckwheat Dolomite. Field of view is 0.6 mm in maximum dimension. Photograph courtesy of Tom Peters and the Paterson Museum.		Figure 21-17. Equant, euhedral pyrite crystal in the white calcite of the Franklin Marble from Franklin. Specimen is 3 cm in maximum dimension. Privately owned. Photo by the author.

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.

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