Retgersite

Chemical formula: Ni²⁺S⁶⁺O₄·₆H₂O

Retgersite is a hydrated nickel sulfate, forming characteristic, emerald-green crystals with a tetragonal structure.

## Characteristics Retgersite is a hydrated nickel sulfate belonging to the epsomite group. It occurs as well-formed, prismatic or pyramidal crystals, as well as granular aggregates, coatings, and efflorescences. Its most characteristic feature is an intense, emerald-green color with a bluish tint. In transmitted light, it becomes pale green. It is a secondary mineral, forming in the oxidation zones of nickel ores. ## Physical Properties Retgersite is a relatively soft mineral, with a hardness of 2.5 on the Mohs scale, meaning it can be scratched with a fingernail. It has a density of 2.04 g/cm³, making it light. It is characterized by a vitreous luster and is transparent to translucent. It exhibits perfect cleavage in one direction. ## Colors and Varieties This mineral is valued for its vivid, emerald-green color, which may have a bluish tint. No named varieties are distinguished, and the coloration is relatively uniform and directly related to the presence of nickel ions in the structure. ## History and Name Retgersite was first described in 1948. Its name honors Jan Willem Retgers (1856-1896), a Dutch crystallographer and mineralogist known for his research on heavy liquids used to determine mineral densities. The type locality (locus typicus) is the Ragra mine in the Huayllay district, Peru. ## Uses Due to its rarity, small crystal sizes, and sensitivity to environmental conditions, retgersite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or nickel minerals.

Properties

Mohs hardness: 2.5
Luster: Vitreous
Streak: Greenish-white
Density: 2.04
Cleavage: On {001}, perfect; traces on {110} in crushed grains under magnification.
Fracture: Irregular/Uneven,Sub-Conchoidal
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Key diagnostic features of retgersite include its intense emerald-green color with a bluish tint, tetragonal crystal form, and low hardness. Its water solubility is also an important indicator. The streak is greenish-white. ## Distinguishing from Similar Minerals Retgersite can be confused with other green, secondary nickel sulfates, such as morenosite (NiSO₄·7H₂O). Morenosite crystallizes in the orthorhombic system and contains more water in its structure, which often leads to faster dehydration. It is distinguished from annabergite (nickel bloom) by its crystal form and hue – annabergite most often forms acicular aggregates with an apple-green color. ## Crystal Forms Retgersite crystals most often occur as short prisms or bipyramids with a square cross-section, typical of the tetragonal system. It also occurs as granular aggregates, coatings, and crusts.

Geological environment

## Genesis Retgersite is a secondary mineral. It forms as a result of the weathering (oxidation) of primary nickel sulfides, such as millerite or pentlandite, in the presence of sulfate-rich waters. It forms as an evaporation product of solutions in dry conditions, often in mine workings. ## Mineral Associations This mineral co-occurs with other secondary sulfates and arsenates. It is most often associated with morenosite, epsomite, gypsum, annabergite, as well as primary nickel and iron sulfides. ## Localities The most important and type locality is the Ragra mine in Peru. It is also known from several other locations worldwide where nickel deposits occur, including the Sudbury region in Ontario (Canada) and some mines in Germany and the Republic of South Africa.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp, and transparent crystals of intense, emerald-green color. Rich crystalline aggregates on a rock matrix are also highly valued. Due to the mineral's instability, it is crucial that the specimen is well-preserved, without signs of dehydration (dulling, cracking). ## Popular Localities Undoubtedly, the most sought-after specimens come from the type locality – the Ragra mine in Peru, from where the best crystals of this mineral are known.

Care and storage

## Cleaning Retgersite is water-soluble, so it must absolutely not be cleaned with water. To remove dust, use only a soft brush or compressed air from a safe distance. ## What to Avoid Avoid contact with water, water vapor, and all chemicals. The mineral is sensitive to changes in humidity – in dry air, it may dehydrate and become dull or disintegrate. Protect it from high temperatures and direct sunlight. ## Storage Retgersite specimens must be stored in airtight, sealed containers (e.g., "membrane boxes" or sealed boxes) to maintain stable ambient humidity. It is best to store it in a dark and cool place.

External references

https://www.mindat.org/min-3489.html