Nickelblödite
Chemical formula: Na<sub>2</sub>Ni<sup>2+</sup>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·4H<sub>2</sub>O
Nickelblödite is a rare, hydrated sodium nickel sulfate, forming characteristic green or blue-green coatings and small crystals.
Description
## Characteristics Nickelblödite is a sulfate mineral, the nickel analog of blödite. It most commonly occurs as brittle, earthy, or fine-grained crusts and efflorescences. Rarely, it forms small, well-developed crystals with a short prismatic or tabular habit. Its most characteristic feature is a vivid apple-green or blue-green color, which immediately indicates the presence of nickel. ## Physical Properties It is a very soft mineral, with a hardness of only 2.5 on the Mohs scale, meaning it can be scratched with a fingernail. It exhibits a vitreous luster and is transparent, unless it occurs in the form of opaque, earthy aggregates. Its density is approximately 2.51 g/cm³. It is brittle and easily susceptible to mechanical damage. ## Colors and Varieties This mineral ranges in color from apple-green to bluish-green. The intensity and hue of the color depend on specific crystallization conditions and potential impurities. No named color varieties or commercial varieties are distinguished. ## History and Name Nickelblödite was first described in 1949 by Federico Ahlfeld and Victorio Angelelli. Its name refers to its chemical composition – the presence of nickel – and its structural similarity to the mineral blödite. The type locality (first discovery) is the San Juan mine in San Juan Province, Argentina. ## Uses Due to its rarity, small size, and physical properties (softness, water solubility), nickelblödite has no industrial applications. It is solely an object of interest for collectors of rare minerals.
Diagnostic features
## Identification Features facilitating the identification of nickelblödite include its characteristic apple-green or bluish-green color, low hardness (2.5 on the Mohs scale), and occurrence as coatings and crusts in paragenesis with other secondary nickel minerals. A definitive, though destructive, test is its solubility in water. ## Distinguishing from Similar Minerals Nickelblödite can be confused with other green, secondary nickel minerals: - **Annabergite:** a nickel arsenate of similar color, but often forming acicular aggregates and occurring in different parageneses. - **Morenosite:** nickel sulfate heptahydrate (NiSO₄·7H₂O), which is even less stable and easily loses water. Distinguishing between the two minerals without specialized tests (e.g., XRD) is very difficult. - **Gaspeite:** a rare nickel carbonate, which is much harder (4.5-5) and reacts with acids. ## Crystal Forms Most commonly found as fine-grained, earthy, or powdery coatings and crusts. Well-formed crystals are very rare, usually small (millimeter-sized), with a short prismatic or tabular habit.
Geological environment
## Genesis Nickelblödite is a secondary mineral. It forms in the oxidation (weathering) zones of nickel ore deposits, such as pentlandite or millerite. This process occurs mainly in arid or semi-arid climates. It can also form as a product of post-mining activity, crystallizing on the walls of old workings and mine dumps from sulfate-rich solutions. ## Mineral Associations It often co-occurs with other secondary sulfate and nickel minerals, such as morenosite, annabergite, gypsum, epsomite, and hexahydrite. ## Localities It is a rare mineral. The most important and classic locality for its occurrence is the type locality – the San Juan mine in Argentina. It has also been reported from several other locations worldwide, usually associated with weathering nickel deposits in dry climatic conditions.
Rarity
Rare
Collector aspects
## Quality Criteria The most highly prized nickelblödite specimens are those with well-formed, transparent crystals of intense green color, even if they are small. Rich, brightly colored crusts covering the matrix rock are also attractive. Crystal size and color saturation are key factors influencing collectible value. ## Popular Localities Specimens from the type locality in San Juan, Argentina, are considered classic and most representative of this mineral.
Care and storage
## Cleaning The mineral is water-soluble, so cleaning requires special care. It must absolutely not be washed with water or other liquids. Dust can only be removed dry, using a very soft brush or a gentle stream of compressed air. ## What to Avoid Contact with water and high humidity must be strictly avoided, as these can cause dissolution or chemical degradation of the specimen. The mineral is also sensitive to high temperatures, which can lead to its dehydration (loss of water from the crystal lattice) and destruction. As a very soft mineral, it is susceptible to scratches and abrasions. ## Storage Nickelblödite specimens should be stored in a dry place, preferably in a tightly sealed container (display case) with a desiccant (e.g., silica gel). Protect from dust, direct sunlight, and sudden temperature changes.