Ernienickelite

Chemical formula: Ni²⁺Mn⁴⁺₃O₇·3H₂O

Ernienickelite is a very rare nickel and manganese oxide, forming microscopic, hexagonal crystals with a metallic luster.

## Characteristics Ernienickelite is a hydrated nickel and manganese oxide, occurring as extremely small, hexagonal, tabular crystals. It typically forms rosette-like or spherulitic aggregates, and individual crystals rarely exceed 0.1 mm in size. Due to its size, its visual characteristics are difficult to observe without a microscope. ## Physical Properties Ernienickelite crystals exhibit a strong, metallic luster. The mineral is opaque. Its hardness and density have not been precisely measured due to the small size of the samples, but the density calculated based on the formula and unit cell parameters is 3.45 g/cm³. ## Colors and Varieties The mineral is black and leaves a black streak. No varieties are known. ## History and Name Ernienickelite was discovered in the dumps of a nickel and cobalt mine in the Widgiemooltha area of Western Australia. It was described in 1994 by Ernest H. Nickel and Bruce W. Robinson. The mineral is named in honor of Dr. Ernest (Ernie) H. Nickel (1925-2009), a Canadian-Australian mineralogist who was one of its discoverers and made significant contributions to mineralogy, particularly in the classification of nickel-bearing minerals. ## Uses Ernienickelite has no industrial applications. It is of interest only to collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
2
Color
Black, red-brown cast.
Luster
Metallic
Streak
yellow-brown
Density
3.84
Cleavage
Perfect on {0001}
Fracture
Splintery
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identification of ernienickelite is impossible without advanced analytical techniques, such as energy-dispersive spectroscopy (EDS/EDX) or X-ray diffraction (XRD), due to its microscopic size and occurrence in complex parageneses. Preliminary indications may include its black color, metallic luster, and hexagonal crystal outline visible under high magnification. ## Distinguishing from Similar Minerals It can be confused with other black manganese oxides, such as pyrolusite, todorokite, or birnessite, with which it often coexists. Definitive differentiation requires chemical analysis confirming the presence of nickel as a key component. ## Crystal Forms Ernienickelite forms very small, thin, hexagonal crystals with a tabular habit. These crystals often combine into rosette-like or spherulitic (spherical) aggregates.

Geological environment

## Genesis Ernienickelite is a secondary mineral, formed in the weathering zone of nickel sulfide deposits. It forms under conditions of strong oxidation in an alkaline or neutral environment (high pH), in the presence of carbonates. It results from the alteration of other nickel minerals, such as violarite or millerite. ## Mineral Associations This mineral coexists with other secondary nickel and manganese minerals. It is most commonly associated with gypsum, goethite, quartz, magnesite, as well as rarer nickel minerals such as takovite, reevesite, violarite, millerite, polydymite, and various manganese oxides (e.g., todorokite). ## Localities The most important and type locality for ernienickelite is the Widgiemooltha mining area in Western Australia, from which the best-formed specimens originate. Its presence has also been noted in several other locations worldwide, including mines in the Attica region of Greece and the Bushveld Igneous Complex in South Africa.

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of ernienickelite primarily depends on the richness and aesthetics of microcrystal aggregates on the rock matrix. The most prized specimens are those showing well-formed, lustrous, rosette-like crystal clusters, contrasting with a lighter background. Due to the microscopic nature of the mineral, the quality of the specimen is assessed under magnification. ## Popular Localities By far the most known and valued specimens come from the type locality – the 132 North mine in Widgiemooltha, Western Australia. Specimens from this location are considered exemplary for this species.

Care and storage

## Cleaning Ernienickelite specimens are extremely delicate and small, so mechanical or chemical cleaning is not recommended. Any attempts at cleaning may destroy the microscopic crystals. It is best to leave them in their untouched state. ## What to Avoid Avoid contact with chemicals, acids, and ultrasonic cleaners. Specimens should be protected from dust and vibrations, which could cause small crystals to detach from the matrix. ## Storage It is recommended to store specimens in sealed, stable "micromount" boxes, which protect against mechanical damage and dust. Avoid exposure to direct sunlight, although there is no evidence of its harmfulness to this particular mineral.

External references

Sources

Read more