Nickelalumite

Chemical formula: Ni₂+Al₄(S₆+O₄)(OH)₁₂(H₂O)₃

Nickelaluminite is a very rare, hydrated nickel and aluminum sulfate, forming characteristic, light blue coatings and crusts.

## Characteristics Nickelaluminite is a secondary mineral, occurring as thin crusts, coatings, and earthy or fibrous aggregates. It typically does not form macroscopic, well-developed crystals. Its appearance is rather inconspicuous, and the main visual feature that attracts attention is its delicate, light blue or bluish-green color, associated with the presence of nickel ions in its structure. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 2.5, meaning it can be scratched with a fingernail. It has a low density, approximately 2.22 g/cm³. The luster is most often dull or earthy, less frequently vitreous on fresh surfaces. It is translucent, and in thicker aggregates, opaque. ## Colors and Varieties Nickelaluminite occurs in uniform shades of light blue, sometimes with greenish tones. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1981 by S. A. Williams. Its name directly refers to its chemical composition – the presence of **nickel** (Latin: *niccolum*) and **aluminum** (Latin: *aluminium*). ## Applications Due to its extreme rarity and occurrence in small quantities, nickelaluminite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 2.5
Luster: Dull
Streak: Pale blue
Density: 2.22
Cleavage: None
Fracture: Earthy
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Helpful features for identifying nickelaluminite include its characteristic light blue color, occurrence in the form of coatings and crusts, very low hardness, and specific environment of occurrence (oxidation zones of nickel deposits). The streak is pale blue. ## Distinguishing from Similar Minerals Nickelaluminite can be confused with other secondary blue nickel minerals, such as retgersite or annabergite, although the latter usually has a more greenish hue. From visually similar copper minerals, like chrysocolla, it is distinguished by significantly lower hardness. Definitive differentiation from very similar sulfates requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms This mineral forms microscopic, tabular crystals aggregated into rosettes, and most often occurs as fine-grained, earthy or fibrous crusts and coatings.

Geological environment

## Genesis Nickelaluminite is a secondary mineral, formed in the oxidation (weathering) zones of nickel ore deposits. It forms as a result of the reaction of acidic, sulfate-rich waters with nickel-bearing minerals and aluminosilicates of the surrounding rocks. ## Mineral Associations It co-occurs with other secondary nickel and iron sulfates, such as retgersite, nickelhexahydrite, morenosite, as well as gypsum and jarosite. ## Localities This is a very rare mineral. The main and typical locality is the Tambillos mining area in Elqui Province, Coquimbo Region, Chile. It has also been reported in small quantities in the Lavrion mines in Greece.

Rarity

Very rare

For collectors

## Quality Criteria For such a rare mineral, the main criterion of value is the richness of the specimen – the larger the surface covered by nickelaluminite coating and the more intense its color, the more valuable the specimen. Specimens where nickelaluminite co-occurs with other rare secondary minerals are also highly prized. ## Popular Localities The vast majority of collector material, including the best quality specimens, comes from the type locality – the Tambillos district in Chile.

Care and storage

## Cleaning Nickelaluminite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water is highly inadvisable. ## What to Avoid Contact with water, acids, and other chemicals should be strictly avoided. As a hydrated mineral, it is sensitive to changes in temperature and humidity, which can lead to its dehydration and disintegration. It is very brittle and soft, so it should be protected from impacts and scratches. ## Storage It is recommended to store specimens in closed, dry containers (e.g., "perky boxes") to stabilize ambient humidity and protect against mechanical damage.

Sources

IMA Mineral List (CNMNC)