Nickelpicromerite

Chemical formula: K₂Ni₂+(S₆+O₄)₂·₆H₂O

Nickelpicromerite is a rare, synthetically produced nickel and potassium sulfate, forming characteristic, green, monoclinic crystals.

## Characteristics Nickelpicromerite is a hydrated nickel and potassium sulfate, belonging to the picromerite group. This mineral forms tabular or short-prismatic crystals, often with well-developed faces. It also occurs as granular aggregates or efflorescences. It is a synthetic analogue of naturally occurring picromerite, in which magnesium has been replaced by nickel, giving it a characteristic, intensely green color. ## Physical Properties Nickelpicromerite crystals are characterized by a vitreous luster and are transparent to translucent. Its hardness on the Mohs scale is approximately 2 to 2.5, making it a very soft mineral. Its density is about 2.23 g/cm³. It is soluble in water. ## Colors and Varieties Nickelpicromerite occurs in various shades of green, from light green to emerald green, depending on the crystallization conditions. Its color is directly related to the presence of nickel(II) ions in the crystal structure. No natural varieties are distinguished, as it is primarily a synthetic substance. ## History and Name The name "nickelpicromerite" refers to its chemical composition – the presence of nickel – and its structural relationship to picromerite. It is a mineral known primarily from laboratory synthesis, and its natural occurrence has not been unequivocally and widely confirmed. In scientific literature, it is described as a member of an isomorphic series with picromerite (magnesium) and cyanochroite (copper). ## Applications Due to its rarity in nature and solubility in water, nickelpicromerite has no industrial applications. However, it is valued by collectors specializing in synthetic or rare minerals, and is also used in scientific research on the crystal chemistry of sulfates.

Properties

Mohs hardness: 2-2.5
Luster: Vitreous
Streak: White
Density: 2.23
Cleavage: Good on {010}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Nickelpicromerite can be identified by its intense green color, relatively low hardness, and characteristic, well-formed crystals. A key diagnostic feature is its solubility in water, which, however, is a destructive test. ## Distinguishing from Similar Minerals It can be confused with other green, secondary nickel minerals, such as annabergite or morenosite. Annabergite is an arsenate and forms acicular crystals, while morenosite (nickel sulfate) has similar properties but crystallizes in the orthorhombic system and is less stable. Varieties of picromerite containing copper (cyanochroite) are blue. ## Crystal Forms It crystallizes in the monoclinic system, forming short-prismatic or tabular crystals. Crystal faces are often flat and shiny. It also occurs as granular aggregates and powdery efflorescences.

Geological environment

## Genesis As a primarily synthetic mineral, nickelpicromerite forms through the slow evaporation of aqueous solutions of nickel sulfate and potassium sulfate under laboratory conditions. Its hypothetical natural occurrence would be associated with weathering processes (oxidation) of nickel-rich sulfide deposits in arid climates, where potassium-rich waters could react with weathering products. ## Mineral Associations Under laboratory conditions, there are no associated minerals. In potential, hypothetical natural occurrences, it could co-exist with other secondary nickel sulfates, such as morenosite, and potassium sulfates. ## Localities There are no confirmed, significant natural occurrences of nickelpicromerite. Specimens available on the collector's market come almost exclusively from controlled laboratory synthesis, often conducted in Poland or the Czech Republic.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are large, well-formed, single crystals with an intense, emerald-green color and high transparency. Attractive groups of crystals grown on a matrix are also desirable. Purity (absence of cracks and inclusions) and lack of mechanical damage are crucial for the value of a specimen. ## Market Prices The prices of synthetic nickelpicromerite specimens are moderate. Small, single crystals or small groups can be acquired for several dozen Polish zlotys. Larger, well-formed specimens with intense color can reach prices of 100-300 Polish zlotys, and exceptional museum-quality pieces may be more expensive. ## Popular Localities The vast majority of specimens on the market come from laboratory synthesis. Some of the most known and aesthetic crystals were grown in laboratories in Poland.

Care and storage

## Cleaning Nickelpicromerite specimens are very sensitive to water, in which they dissolve. Cleaning is highly inadvisable. If absolutely necessary, compressed air can be used to remove dust or the surface can be very gently wiped with an extremely soft-bristled brush. ## What to Avoid Contact with water, water vapor, and all liquids must be strictly avoided. The mineral is hygroscopic and can absorb moisture from the air, leading to its slow disintegration. It should be protected from high temperatures, which can cause the loss of hydration water and destruction of crystals. Also avoid direct sunlight. ## Storage Specimens should be stored in a dry place, preferably in an airtight, sealed container (e.g., a "membrane box") or in a box with a desiccant (silica gel). Storage under conditions of low relative humidity is crucial for maintaining the integrity of the specimen.

Sources

IMA Mineral List (CNMNC)