Arupite

Chemical formula: Ni₂+₃(PO₄)₂·₈H₂O

A very rare, hydrated nickel phosphate, forming delicate, green coatings and aggregates of acicular crystals.

## Characteristics Arupite is a hydrated nickel phosphate belonging to the vivianite group. It most commonly occurs as delicate, brittle coatings and crusts, resembling efflorescences. It also forms small aggregates of radial or tangled masses, composed of tiny, acicular or platy crystals. Due to the small size of its crystals, specimens are most often appreciated in micromineralogical form. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2.5. It exhibits a vitreous luster, which can transition to pearly on surfaces of perfect cleavage. It is transparent to translucent. Its specific gravity is 2.83 g/cm³. ## Colors and Varieties Arupite ranges in color from light green and apple-green to greenish-blue. It is the nickel analog of iron-rich vivianite and cobalt-rich erythrite. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1980 by S.Y. Chow, J.D. Grice, and J.A. Tanco. The name "arupite" honors the Italian Arup family, particularly Dr. Giancarlo Arup, in recognition of their contributions to the development of mineralogy and support for scientific research. ## Uses Due to its extreme rarity and occurrence in small quantities, arupite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 2.5
Luster: Vitreous, Pearly
Streak: Light green
Density: 2.83
Cleavage: Perfect on {010}
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of arupite include its light green color, occurrence as delicate coatings and acicular aggregates, very low hardness, and specific environment of occurrence. It is a secondary mineral in the oxidation zones of nickel deposits. ## Distinguishing from Similar Minerals Arupite is visually almost indistinguishable from annabergite (Ni₃(AsO₄)₂·8H₂O), with which it often co-occurs. Annabergite is an arsenate, while arupite is a phosphate, so their definitive distinction requires chemical analysis (e.g., EDS). It differs from vivianite (usually blue, contains iron) and erythrite (pink to carmine, contains cobalt). ## Crystal Forms It forms very small, acicular (elongated along the c-axis) or platy crystals, which combine into radial aggregates, tangled masses, crusts, and coatings.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones (gossan) of nickel ore deposits. It forms as a result of weathering and alteration processes of primary nickel sulfides, such as pentlandite or millerite, under the influence of phosphate-rich waters. ## Mineral Associations Arupite often co-occurs with other secondary nickel and cobalt minerals. Typical associated minerals include annabergite, morenosite, as well as primary sulfides like pentlandite, millerite, nickeline, gersdorffite, and gypsum. ## Localities The most important and classic locality (type locality) is the Carr Boyd Rocks nickel-copper mine, located west of Kalgoorlie in Western Australia. It is an extremely rare mineral, and confirmed occurrences outside the type locality are few.

Rarity

Very rare

For collectors

## Quality Criteria The quality of arupite specimens, which are almost always micromounts, is assessed based on the richness of the coating, the size and development of microcrystals within aggregates, and the aesthetic composition with associated minerals. The intensity and purity of the green color also increase the value of the specimen. ## Popular Localities The vast majority, if not all, collector specimens come from the type locality – the Carr Boyd Rocks mine in Western Australia. Finds from other locations are rare and are primarily of scientific importance.

Care and storage

## Cleaning Arupite specimens are extremely delicate and soft. To remove dust, use only a soft brush or a stream of compressed air from a safe distance. Avoid contact with water; if absolutely necessary, very brief contact with distilled water followed by immediate drying is permissible. ## What to Avoid Arupite is sensitive to chemicals and readily dissolves in acids. It should be protected from high temperatures and direct sunlight, which can lead to dehydration and destruction of the crystal structure. Ultrasonic cleaners must not be used. ## Storage It is recommended to store specimens in a dry, stable environment, in a sealed "micromount" box, to protect them from dust, mechanical damage, and sudden changes in humidity.

Sources

IMA Mineral List (CNMNC)