Nickelbischofite

Chemical formula: Ni₂+Cl₂·₆H₂O

Nickelbischofite is a rare, water-soluble nickel chloride, forming green, acicular crystals and efflorescences in high-humidity environments.

## Characteristics Nickelbischofite is a hydrated nickel chloride, occurring as delicate, acicular or hair-like crystals. It typically forms fibrous aggregates, coatings, crusts, and efflorescences on other minerals. Due to its hygroscopic nature and water solubility, it is an unstable mineral that can only exist under conditions of very high atmospheric humidity or in hermetically sealed spaces, such as rock cavities. ## Physical Properties Nickelbischofite crystals are very soft and brittle. This mineral is strongly hygroscopic, meaning it absorbs moisture from the air, which can lead to its dissolution. It has a density close to 1.92 g/cm³. It is characterized by a vitreous luster. ## Colors and Varieties Nickelbischofite has a characteristic, intensely green or bluish-green color, typical of hydrated nickel compounds. No varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition (nickel content) and its structural similarity to bischofite (MgCl₂·6H₂O). It was first described in 1979 by J.D. Grice and H.F. Steacy based on material from the Thompson mine, Manitoba, Canada, where it was found as early as 1971. It was approved as a new mineral by the IMA in 1978. ## Uses Nickelbischofite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and scientists studying secondary nickel minerals.

Properties

Mohs hardness: 1.5-2
Luster: Vitreous
Streak: White
Density: 1.924
Cleavage: Perfect on {110}
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Nickelbischofite can be identified by its intense green color, acicular or fibrous form, and its instability under normal atmospheric conditions. Its extreme water solubility is a key diagnostic feature – a drop of water on the mineral's surface will cause it to disappear. It reacts violently with hydrochloric acid. ## Distinguishing from Similar Minerals It can be confused with other secondary, green nickel minerals, such as annabergite (nickel arsenate) or zaratite (nickel carbonate). Annabergite, however, is much harder and does not dissolve in water. Zaratite is also insoluble and usually forms spherical or reniform aggregates, not acicular ones. ## Crystal Forms Crystals are usually very small, elongated in the form of needles or hairs. They form fibrous aggregates, radial aggregates, as well as crusts and efflorescences.

Geological environment

## Genesis Nickelbischofite is a secondary mineral, formed as a result of weathering or oxidation processes of primary nickel sulfides (mainly pentlandite and millerite) in the presence of chloride-rich solutions. It forms under low-temperature and very high-humidity conditions, often as a post-mining product in nickel ore mines, where it precipitates on mine walls, waste rock, or old mining tools. ## Mineral Associations It most commonly co-occurs with the minerals from which it forms, i.e., pentlandite and millerite. It is also accompanied by other sulfides, such as pyrite and pyrrhotite, as well as other secondary nickel minerals, e.g., morenosite (nickel sulfate). ## Localities The most important and best-documented occurrences of this mineral are nickel mines. It was discovered in the Thompson mine in Manitoba, Canada (type locality). It is also known from several mines in Germany (e.g., Saxony and North Rhine-Westphalia), from Greece (in the Attica region), and from mine dumps in Pennsylvania, USA.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of nickelbischofite primarily depends on the abundance and quality of crystal formation. The most valued specimens are those with visible, well-formed needles of intense green color, forming rich coatings on the host rock. Due to the mineral's instability, it is crucial that the specimen is well-preserved and properly secured. Contrast with the rock matrix also enhances visual value. ## Popular Localities The type locality in Thompson, Manitoba (Canada) is considered classic and yields the best specimens. Specimens from German mines are also known in collections.

Care and storage

## Cleaning This mineral must absolutely not be cleaned wet. Any contact with water, even in the form of a damp cloth, will cause its immediate dissolution. Specimens are not mechanically cleaned due to their extreme delicacy. ## What to Avoid Above all, moisture and water should be avoided. The mineral is strongly hygroscopic and absorbs water from the air, leading to its deliquescence (dissolution in absorbed water). It should be protected from changes in humidity, elevated temperatures, and direct sunlight. ## Storage Nickelbischofite specimens must be stored in hermetically sealed containers, preferably with a desiccant (e.g., silica gel), to ensure very low ambient humidity. This is the only way to preserve the specimen in a solid state long-term.

Sources

IMA Mineral List (CNMNC)