Nickeline

Chemical formula: NiAs

Nickel arsenide with a characteristic copper-red color and metallic luster, an important nickel ore.

## Characteristics Nickeline, also known as niccolite, is a nickel arsenide (NiAs), a mineral belonging to the nickeline group. It typically forms massive, granular, or reniform aggregates. Well-formed crystals are rare and take the form of hexagonal prisms or tabular crystals, often terminated by pyramids. Its most recognizable feature is its characteristic pale copper-red color, which quickly tarnishes on a fresh surface, becoming covered with a black coating (annabergite) or a greenish one (nickel bloom). ## Physical Properties This mineral is opaque and exhibits a strong, metallic luster. It is relatively hard, with a Mohs hardness of 5 to 5.5, placing it in the same category as apatite. Its density is significant, approximately 7.8 g/cm³, which makes specimens heavy for their size. ## Colors and Varieties The dominant and essentially sole color of nickeline is pale copper-red, often with a pink or violet hue. The name "Kupfernickel" (copper nickel) reflects this characteristic. No distinct color varieties or commercial varieties are recognized, although it is sometimes confused with breithauptite (NiSb), which has a similar but more violet hue. ## History and Name The historical name "Kupfernickel" comes from medieval German miners in Saxony. They found a mineral resembling copper ore ("Kupfer") but could not extract this metal from it. They believed it was the work of mischievous gnomes or mine spirits ("Nickel"), hence "Nick's copper" or "devil's copper." In 1751, the Swedish chemist Axel Fredrik Cronstedt successfully isolated a new element from this mineral, which he named nickel in honor of this history. The formal name "nickeline" was introduced in 1832 by François Sulpice Beudant. ## Uses Nickeline is an important component of some nickel deposits and historically was a significant ore of this metal. Today, its importance as an ore is diminished, but it remains an important indicator mineral in the search for nickel, cobalt, and silver deposits. For collectors, it is a prized mineral due to its historical significance and distinctive appearance.

Properties

Mohs hardness
5-5.5
Luster
Metallic
Streak
Brownish-black
Density
7.8-7.86
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Hexagonal

Diagnostic features

## Identification The key diagnostic feature of nickeline is its unique, pale copper-red color combined with a strong metallic luster. It is a relatively heavy and hard mineral. Also characteristic is its tendency to tarnish and become covered with a greenish coating of annabergite (nickel bloom) or a black coating of oxides. ## Distinguishing from Similar Minerals Nickeline is sometimes confused with bornite, which, however, exhibits strong iridescence (a variegated play of colors) and is softer. Breithauptite (NiSb) has a very similar appearance, but its color is distinctly more violet or violet-pink. Pyrite (FeS₂) is lighter, brass-yellow. Chalcopyrite (CuFeS₂) is also more yellow and softer. Rhodonite has a similar color but a vitreous luster and is a silicate. ## Crystal Forms Crystals are rare, hexagonal, with a prismatic or tabular habit. It most often occurs in massive, compact aggregates, often with a reniform or botryoidal structure. It also occurs as inclusions in other sulfides and arsenides.

Geological environment

## Genesis Nickeline is a typical hydrothermal mineral of medium to high temperatures. It forms in ore veins, often in association with other nickel, cobalt, and silver sulfides and arsenides. It also occurs in ultramafic igneous rocks, such as norites, where it crystallizes from sulfide-rich magma (magmatic deposits). ## Mineral Associations This mineral often co-occurs with other arsenides, such as skutterudite, safflorite, rammelsbergite, and löllingite. It is also frequently accompanied by chalcopyrite, pyrite, pyrrhotite, native silver, native bismuth, and minerals from the cobaltite-gersdorffite group. In the weathering zone, it oxidizes to green annabergite. ## Localities Historically important and classic localities include Germany (Schneeberg, Annaberg in Saxony; St. Andreasberg in the Harz Mountains) and the Czech Republic (Jáchymov). Significant deposits where nickeline occurs include the Sudbury region in Ontario (Canada), Cobalt in Ontario (Canada), as well as deposits in Argentina (Vinchina), Morocco (Bou Azzer), and Australia.

Rarity

Not very common

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp hexagonal crystals, which are very rare. Rich, massive aggregates with an intense, fresh copper-red color, without signs of oxidation, are also highly valued. Contrast with other minerals, such as white calcite, quartz, or silvery cobalt arsenides, enhances their attractiveness. Specimens from classic, historical localities, such as Saxony, are particularly sought after. ## Popular Localities For collectors, the most desirable specimens come from historical German and Czech mining regions, such as Schneeberg, Annaberg, and Jáchymov. Currently, beautiful, crystalline specimens are supplied from the Bou Azzer region in Morocco. Massive, rich ores come from the Sudbury and Cobalt regions in Canada.

Care and storage

## Cleaning Nickeline should only be cleaned dry, using a soft brush or compressed air to remove dust. Contact with water, especially with detergents, can accelerate the oxidation process and lead to the formation of undesirable coatings. ## What to Avoid Contact with water, acids, and other chemicals should be strictly avoided. The mineral is sensitive to moisture and oxygen, which causes it to tarnish and become covered with secondary nickel minerals. It should not be heated, as this can lead to the emission of toxic arsenic fumes. It should be protected from prolonged exposure to humid air. ## Storage Nickeline specimens are best stored in dry, airtight containers, such as membrane boxes or display cases with a desiccant. Display should be in enclosed cabinets, away from sources of moisture and sudden temperature changes. Due to its arsenic content, it is recommended to wash hands after contact with the mineral.

External references

Sources

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