Reevesite

Chemical formula: Ni<sup>2+</sup><sub>6</sub>Fe<sup>3+</sup><sub>2</sub>(OH)<sub>16</sub>CO<sub>3</sub>·4H<sub>2</sub>O

Reevesite is a mineral of the hydrotalcite group, a hydrated nickel and iron carbonate, forming characteristic, lemon-yellow coatings and small, hexagonal crystals.

## Characteristics Reevesite is a secondary mineral belonging to the hydrotalcite supergroup. It most often occurs as thin coatings, crusts, or earthy aggregates of an intense, lemon-yellow to canary-yellow color. Less frequently, it forms small rosettes composed of tiny, platy crystals with a hexagonal outline. ## Physical Properties It is a very soft mineral, with a hardness of only 2 on the Mohs scale. It is characterized by a waxy or pearly luster on fracture surfaces and perfect cleavage. It is translucent, and its density is approximately 2.89 g/cm³. ## Colors and Varieties The dominant color is yellow in various shades, from light yellow to intense lemon-yellow. There are no named color varieties or commercial varieties. ## History and Name The mineral was described in 1967 by J.J. Fahey, E.J. Dwornik, and J.F. Mrose. Its name honors Frank Reeves (1886-1986), a geologist who discovered the Wolfe Creek meteorite crater in Australia. Reevesite was first isolated and described from material originating from the nickel-iron meteorite found there. ## Uses Due to its rarity and small crystal size, reevesite has no industrial application. It is solely an object of scientific interest and a valued collector's stone.

Properties

Mohs hardness
2
Luster
Waxy, Pearly
Streak
Light yellow
Density
2.89
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Key diagnostic features include: intense yellow color, low hardness, occurrence as coatings or small, hexagonal plates, and its characteristic environment of occurrence (serpentinite rocks or iron meteorites). ## Distinguishing from Similar Minerals It can be confused with other secondary yellow minerals, such as jarosite. However, it is distinguished by its significantly lower hardness. Identification can be difficult without specialized tests, especially when distinguishing it from other, rarer members of the hydrotalcite supergroup. ## Crystal Forms It most often forms microcrystalline coatings and crusts. Well-formed crystals are rare, appearing as thin, hexagonal plates, often gathered in small, rosette-like aggregates.

Geological environment

## Genesis Reevesite is a secondary mineral. It forms in two main types of environments: as a product of weathering of nickel-iron meteorites and as a result of low-temperature, hydrothermal alteration of serpentinized ultramafic rocks, where it forms at the expense of alteration of nickel sulfides (e.g., millerite). ## Mineral Associations In meteorites, it is associated with goethite, maghemite, and native iron. In serpentinites, it co-occurs with serpentine group minerals, chromite, millerite, and other minerals from the hydrotalcite supergroup, such as pyroaurite or iowaite. ## Localities The most important localities worldwide include the discovery site at Wolfe Creek crater in Western Australia, the Bon Accord deposit in South Africa, the Cedar Hill quarry in Pennsylvania (USA), as well as Mont Saint-Hilaire in Canada and Val Malenco in Italy.

Rarity

Not very common

For collectors

## Quality Criteria The most prized specimens are those with well-formed, visible to the naked eye hexagonal crystals or aesthetic rosettes. The intensity and purity of the lemon-yellow color significantly increase the value of the specimen, as does an attractive contrast with the minerals of the host rock. ## Popular Localities The localities of Bon Accord (South Africa) and Mont Saint-Hilaire (Canada) are considered classic, providing the best collector's specimens. Specimens from the type locality (Wolfe Creek) have historical value.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush. Distilled water can be used to remove dirt. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is very soft and susceptible to scratching. As a carbonate, it reacts with acids. It is also sensitive to high temperatures, which can cause the loss of water from its structure. It should be protected from impacts due to its perfect cleavage. ## Storage It is recommended to store specimens in separate, padded boxes to avoid contact with harder minerals and prevent mechanical damage.

Sources

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