Nickelboussingaultite

Chemical formula: (N₃-H₄)₂Ni₂+(S₆+O₄)₂·₆H₂O

Nickelboussingaultite is a hydrated nickel ammonium sulfate, a rare secondary mineral characterized by its bright green color.

## Characteristics Nickelboussingaultite is a hydrated nickel ammonium sulfate, belonging to the picromerite group. It forms small, well-developed crystals with a short prismatic or tabular habit, and also occurs as granular aggregates, coatings, and efflorescences. It is a brittle mineral, with a bright green, greenish-blue, or yellowish-green color, which is its most characteristic visual feature. ## Physical Properties Nickelboussingaultite crystals exhibit a vitreous luster. This mineral is relatively soft, with a Mohs hardness of 2.5. It is transparent to translucent. Its density ranges from 1.913 to 1.933 g/cm³. It is soluble in water. ## Colors and Varieties This mineral occurs in shades from bright green and yellowish-green to greenish-blue. No named color varieties or commercial varieties are distinguished. ## History and Name Nickelboussingaultite was first described in 1930 by A. N. Winchell. Its name refers to its chemical composition – the presence of nickel – and its structural similarity to the mineral boussingaultite, which in turn was named after the French chemist Jean-Baptiste Boussingault. It is the nickel analog of boussingaultite.

Properties

Mohs hardness: 2.5
Luster: Vitreous
Streak: White
Density: 1.913-1.933
Cleavage: Good on {010}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Nickelboussingaultite can be identified by its characteristic bright green color, relatively low hardness, and occurrence as small crystals, coatings, and efflorescences in specific environments. A key diagnostic feature is its solubility in water. ## Distinguishing from Similar Minerals It can be confused with other secondary nickel sulfates, such as morenosite (NiSO₄·7H₂O) or retgersite (NiSO₄·6H₂O). Differentiation often requires chemical or crystallographic analysis. It differs from annabergite (nickel bloom) by its crystal habit and environment of occurrence (annabergite forms in the oxidation zones of nickel ore deposits). ## Crystal Forms Crystals are usually small, with a short prismatic or tabular habit. It is most commonly found as granular aggregates, crusts, coatings, and efflorescences on rock surfaces.

Geological environment

## Genesis Nickelboussingaultite is a secondary mineral, formed by the activity of volcanic fumaroles, where hot gases rich in sulfur compounds and ammonia react with nickel-bearing rocks. It also forms as a product of burning mine dumps, especially in coal mines, where at high temperatures, reactions occur between sulfides, nickel compounds, and ammonia from organic matter. ## Mineral Associations It often co-occurs with other sulfates formed under similar conditions, such as boussingaultite, mascagnite, and also native sulfur. ## Localities Important localities for this mineral include Vesuvius in Italy (as a product of fumarolic activity), as well as burning mine dumps, e.g., in Svatá Kateřina in the Czech Republic; in Pennsylvania (USA); and in Pécs, Hungary.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, transparent crystals of intense, bright green color. Contrastive placement of crystals on the rock matrix also enhances their appeal. Due to the small size of the crystals, micromount specimens are standard. ## Popular Localities Specimens from classic fumarolic localities, such as Vesuvius, are historically and scientifically valuable. Good quality microcrystals also come from some burning dumps in the Czech Republic and Hungary.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to its solubility in water, absolutely avoid contact with water and other liquids. ## What to Avoid Avoid contact with water, moisture, and chemicals that can dissolve or damage the mineral. Store away from heat sources and direct sunlight, which can lead to dehydration and loss of color. ## Storage Nickelboussingaultite specimens require storage in dry conditions, preferably in a sealed, airtight container (a "membrane box" or a box with a desiccant), to protect them from atmospheric moisture. Avoid storing in places with fluctuating temperature and humidity.

Sources

IMA Mineral List (CNMNC)