Aerugite

Chemical formula: Ni₂+₈.₅(As₅+O₄)₂As₅+O₈

An extremely rare nickel arsenate, forming intensely green, emerald-like coatings and crusts in the oxidation zones of ore deposits.

## Characteristics Aerugite is a very rare mineral from the arsenate group, chemically a complex nickel arsenate. Its name, derived from the Latin word *aerugo* meaning "copper rust," accurately reflects its most characteristic feature—an intense, emerald or apple-green color. It typically occurs as microcrystalline, massive, or earthy coatings and crusts on other minerals. Well-formed crystals are extremely rare and microscopic in size. ## Physical Properties This mineral is characterized by relatively low hardness, 4 on the Mohs scale, and significant density, ranging from 5.85 to 5.95 g/cm³. Its luster is described as vitreous, and on some surfaces, greasy. In thin fragments, it can be translucent, but in mass, it is usually opaque. ## Colors and Varieties Aerugite occurs in various shades of green, from bright, emerald green to a darker, apple green. It does not form color varieties or commercial varieties—it is valued exclusively as a rare collector's specimen. ## History and Name The mineral was first described by Gilbert Joseph Adam in 1869. The name refers to its vivid green color, resembling the patina that forms on copper alloys.

Properties

Mohs hardness: 4
Luster: Vitreous to Greasy
Streak: Greenish gray
Density: 5.85-5.95
Cleavage: None
Fracture: Uneven to Subconchoidal
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key features for identifying aerugite are its intense, emerald-green color, occurrence as coatings and crusts, high density, and paragenesis with other nickel and arsenic minerals. The streak has a characteristic greenish-gray color. ## Distinguishing from Similar Minerals Aerugite is sometimes confused with other green, secondary arsenates, mainly annabergite (nickel bloom). However, annabergite is hydrated, has a lower density, usually a lighter shade of green, and often forms acicular aggregates, whereas aerugite is massive. Bunsenite (nickel oxide) can also be green, but it is significantly harder (5.5 on the Mohs scale). Certain differentiation of these minerals often requires advanced studies, such as X-ray diffraction (XRD). ## Crystal Forms Aerugite almost exclusively forms massive, earthy, or microcrystalline aggregates in the form of coatings and crusts. Very rarely, small, imperfectly formed trigonal crystals are observed.

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal deposits rich in arsenic and nickel. It forms as a result of the alteration of primary nickel arsenides, such as niccolite. ## Mineral Associations Aerugite often co-occurs with minerals typical of its formation environment. Its most common associations include niccolite, annabergite, bunsenite, erythrite, roselite, quartz, and native bismuth. ## Localities This is an extremely rare mineral, known from only a few localities worldwide. The type locality is Johanngeorgenstadt in Saxony (Germany). Other significant occurrences include the Tsumeb mine in Namibia and other localities within the Ore Mountains (Erzgebirge) on the German-Czech border.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity, every aerugite specimen is valuable to systematic mineral collectors. The value is primarily determined by the richness of the coating—its surface area and thickness. Specimens with an intense, emerald color and those associated with other rare or well-formed minerals are more highly prized. ## Popular Localities The most sought-after by collectors are specimens from classic, historical localities in Germany (Johanngeorgenstadt) and from the Tsumeb mine in Namibia, known for supplying many rare and unique minerals.

Care and storage

## Cleaning Aerugite specimens should only be cleaned mechanically, using a soft brush to remove dust and loose debris. Very careful wiping with a damp cloth and distilled water is permissible, but submerging the mineral in water should be avoided. ## What to Avoid Aerugite is an arsenate and is toxic. Inhaling dust, ingestion, and contact with mucous membranes should be avoided. Hands should be thoroughly washed after any contact with the mineral. The mineral is sensitive to acids, which can damage or dissolve it. It should not be heated or exposed to strong chemicals. ## Storage It is recommended to store specimens in closed, labeled containers (e.g., "micromount" boxes) to limit contact and prevent accidental dusting. It should be kept away from children and pets.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FAerugite