Pararammelsbergite

pararammelsbergite

skutterudite

nickeline

gersdorffite

Formula: NiAs2
Arsenide, löllingite group, low temperature orthorhombic paramorph of isometric krutovite and high temperature orthorhombic rammelsbergite
Crystal System: Orthorhombic
Specific gravity: 7.12 measured, 7.24 calculated
Hardness: 5½
Streak: Greyish black
Colour: Tin-white
Common impurities: Co,Cu,S
Environments

Hydrothermal environments

Pararammelsbergite occurs in hydrothermal veins bearing nickel-cobalt sulphide mineralisation. Associated minerals include nickeline, skutterudite, cobaltite, löllingite, gersdorffite and rammelsbergite (HOM).

Localities

There are three co-type Localities, the Hudson Bay mine, Coleman Township, Cobalt area, the Moose Horn mine, James Township, Elk Lake area, and the Keeley-Frontier mine, South Lorrain Township, all in the Cobalt-Gowganda region, Timiskaming District, Ontario, Canada.

At the Hudson Bay mine, one specimen consists almost entirely of pararammelsbergite. The associated minerals are skutterudite, cobaltite and gersdorffite (?) which tend to form rims outlining the margin of the main mass of pararammelsbergite. In a section from another specimen, the cubic minerals, together with löllingite, constitute about one-half of the surface. Typical pararammelsbergite occupies the centres of spheroidal areas which are separated by the cubic minerals and löllingite (AM 25.561-577).

At the Moose Horn mine, a specimen section consists almost whoily of pararammelsbergite, associated with interstitial nickeline and skutterudite in isolated grains and seams. (AM 25.561-577).

At the Keeley mine, in a specimen with a reniform structure, the central part consists of pararammelsbergite while the rim is made up of skutterudite and gersdorffite (?) (AM 25.561-577).

Alteration

Pararammelsbergite is the lower temperature paramorph of rammelsbergite with an inversion temperature of 590oC in equilibrium with nickeline. This inversion temperature is appreciably lowered by inclusion of small quantities of cobalt and sulphur in the lattice (CM 9.128-131).

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