GERSDORFFITE

NiAsS
Cubic

Gersdorffite was originally reported from Franklin by Holmes (1945) and likely comprised a small part of the material referred to as chloanthite by Koenig (1889) and Palache (1935). Gersdorffite was studied in detail by Oen et al. (1984). It is not known from Sterling Hill and is a rare mineral locally.

Description

Gersdorffite is gray, opaque, and very fine-grained (Figures 21-33 and 21-34). It occurs in bands up to 0.5 cm in width, but is not easily discernible from rammelsbergite without optical or X-ray techniques.

Composition

Gersdorffite is a nickel arsenic sulfide mineral. Fe and Co substitute for nickel, in some specimens extensively, and there is minor Sb present in most specimens. Extensive analytical data were given by Oen et al. (1984), and several representative analyses are given in Table 18.

Occurrence and paragenesis

At Franklin, gersdorffite occurs in the nickel-arsenide assemblage, found but once, most recently described by Oen et al. (1984) and discussed in detail herein under nickeline. Gersdorffite occurs as a part of dendrites which have general growth sequences (toward the exterior) of nickeline ® rammelsbergite ® gersdorffite ® nickel-rich loellingite (Figures 21-33 and 21-34). Several generations of gersdorffite are present in some specimens, with the outermost zone being richer in Fe and Co than the more nickel-rich inner zones. Extensive textural detail was provided by Oen et al. (1984).

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