Nickelskutterudite

Chemical formula: NiAs<sub>3</sub>

A nickel arsenide from the skutterudite group, forming metallic, tin-white or steel-gray crystals in the isometric system.

## Characteristics Nickelskutterudite is a nickel arsenide, being the nickel-dominant end-member of the skutterudite isomorphic series. It rarely occurs in its pure form, most often forming solid solutions with cobalt-dominant skutterudite. It forms well-developed, lustrous crystals with a metallic appearance. Its surface often becomes tarnished or acquires an iridescent sheen due to oxidation. ## Physical Properties This mineral is relatively hard and brittle. It is characterized by a strong metallic luster and high density, approximately 6.9 g/cm³. It is completely opaque. Due to its metallic nature, it is a good electrical conductor. ## Colors and Varieties Nickelskutterudite ranges in color from tin-white to steel-gray, sometimes with a yellowish tint. On weathered surfaces, a black tarnish or iridescent patina may appear. Historically, it was known as **chloanthite**, a name now discredited by the International Mineralogical Association (IMA) in favor of the systematic name. ## History and Name The name "nickelskutterudite" directly refers to its chemical composition (dominant nickel) and its belonging to the skutterudite group. The name of the parent mineral, skutterudite, comes from its type locality in Skuterud, Norway. The term "chloanthite" was abandoned to standardize nomenclature within the group. ## Applications Due to its rarity, nickelskutterudite currently has no significance as a source of nickel. In the past, ores rich in skutterudite group minerals were exploited for cobalt and nickel. Today, it is primarily an object of interest for collectors and scientists.

Properties

Mohs hardness
5.5-6
Luster
Metallic
Streak
Black
Density
~6.9
Cleavage
Good on {001} and {111}
Fracture
Uneven to conchoidal
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Characteristic features of nickelskutterudite include its high density, metallic luster, tin-white color, and isometric crystal habit. The streak is black. It occurs in specific association with other nickel and cobalt arsenides. ## Distinguishing from Similar Minerals Macroscopic differentiation of nickelskutterudite from skutterudite (cobalt-dominant) is practically impossible without advanced chemical analyses (e.g., EDS). It can be confused with other metallic arsenides, such as safflorite, rammelsbergite, or löllingite. A key indicator is the isometric crystallographic system of nickelskutterudite, whereas many similar minerals crystallize in other systems (e.g., orthorhombic). ## Crystal Forms It crystallizes in the isometric system, most often forming cubes, octahedra, rhombic dodecahedra, and their combinations. It also occurs as granular aggregates, massive forms, as well as dendrites and radial aggregates.

Geological environment

## Genesis Nickelskutterudite forms under moderate-temperature hydrothermal conditions. It is a component of ore veins rich in nickel, cobalt, silver, and arsenic. ## Mineral Associations It most often co-occurs with other minerals from the skutterudite group, as well as with nickeline, gersdorffite, rammelsbergite, safflorite, löllingite, arsenopyrite, native silver, native bismuth, and also with calcite, dolomite, and quartz. ## Localities Important global localities include historical deposits in the Ore Mountains (Erzgebirge) in Germany (especially Schneeberg and Annaberg). Significant specimens also come from the Cobalt region in Ontario (Canada), where they occurred in silver-arsenide veins. Other known occurrences include Bou Azzer in Morocco and mines around Skuterud in Norway.

Rarity

Rare

For collectors

## Quality Criteria Specimens with sharp, well-formed crystals and a strong, metallic luster are most highly valued. The absence of damage and a clean, unoxidized surface are of great importance. Crystal intergrowths of nickelskutterudite with other minerals are exceptionally attractive, especially with color-contrasting native silver, pink erythrite (a weathering product of cobalt arsenides), or white calcite. ## Popular Localities Specimens from the German Ore Mountains and Cobalt, Canada, are considered classic and are sought after by collectors due to their historical significance. Currently, beautiful, well-formed crystals are supplied from the Bou Azzer region in Morocco.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water, especially with detergents, can accelerate the oxidation process and lead to dulling or discoloration of the surface. ## What to Avoid Nickelskutterudite is a toxic mineral due to its high arsenic content. Avoid inhaling dust generated during its handling or cleaning. After each contact with a specimen, hands must be thoroughly washed. The mineral is sensitive to moisture and acidic environments, which cause its deterioration. ## Storage It is recommended to store specimens in a dry place, preferably in closed, airtight containers or display cases, to limit air and moisture access. This protects against oxidation and dulling, and also reduces the risk of accidental contact with the toxic mineral.

External references

Sources

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