Niasite

Chemical formula: Ni²⁺₄.₅(As⁵⁺O₄)₃

Niasite is a very rare nickel arsenate, distinguished by its intense, violet-red to red-orange color.

## Characteristics Niasite is a nickel arsenate that visually presents as small, tabular crystals not exceeding 0.2 mm in size. It forms aggregates and coatings on the rock substrate. Its most characteristic feature is its intense, violet-red to red-orange color. ## Physical Properties Niasite crystals exhibit a vitreous luster and are transparent. This mineral has a hardness of 4 on the Mohs scale, and its density, calculated from crystallographic data, is 5.22 g/cm³. The fracture is conchoidal. ## Colors and Varieties Niasite occurs in uniform, vivid colors in the spectrum from violet-red to red-orange. No varieties have been distinguished. ## History and Name The name "niasite" is an acronym derived from the mineral's chemical composition: nickel (Ni) and arsenic (As). It was first described in 1995 by J. Schlömann, K.-H. Witzke, T. Doering, and M. Steins. The type locality (locus typicus) was designated as Johanngeorgenstadt in the Ore Mountains (Saxony, Germany).

Properties

Mohs hardness
4
Luster
Vitreous
Streak
pale pink
Density
5.222
Fracture
Conchoidal
Transparency
Transparent
Crystal system
Tetragonal

Diagnostic features

## Identification Niasite can be identified by its characteristic, intense violet-red or red-orange color, tabular crystal habit, and occurrence in association with other nickel and arsenic minerals. The streak is pale yellowish. ## Distinguishing from Similar Minerals It can be confused with other secondary nickel arsenates, such as nickel erythrite (annabergite), which, however, has a green color. Differentiation from other reddish arsenates requires advanced analytical methods (e.g., EDS/XRD). ## Crystal Forms Niasite forms very small, thin, tabular crystals that often arrange into rosette-like or radial aggregates. It also occurs as thin coatings and efflorescences.

Geological environment

## Genesis Niasite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal ore deposits rich in nickel and arsenic. It forms as a result of alterations of primary minerals of these elements. ## Mineral Associations At the type locality in Germany, niasite co-occurs with quartz, barite, annabergite, aerugite, bunsenite, xanthiosite, rooseveltyte, nickel skutterudite, and native nickel. ## Localities The only confirmed and thoroughly described occurrence of niasite in the world is its type locality: Johanngeorgenstadt in the Erzgebirgskreis district, Saxony (Germany).

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity, every analytically confirmed niasite specimen is valuable to specialized collectors. Specimens with well-formed crystals, despite their small size, that form rich aggregates and exhibit intense, vivid coloration are most highly prized. The aesthetics of the host rock and the presence of associated minerals are also important. ## Popular Localities The only source of specimens is the historical type locality in Johanngeorgenstadt, Germany. Collector material is practically unavailable on the market.

Care and storage

## Cleaning Due to its extreme rarity and small crystal size, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. ## What to Avoid Avoid contact with acids and all chemicals. As an arsenate, niasite is toxic and should be handled with utmost caution, avoiding dust inhalation and direct skin contact. ## Storage Specimens should be stored in tightly sealed containers, such as micromineral boxes, away from moisture and with an appropriate toxicity warning label.

External references

Sources

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