Nepskoeite

Chemical formula: Mg₄Cl(OH)₇·₆H₂O

Nepskoeite is a rare hydrated magnesium hydroxychloride, forming tiny, acicular crystals and fibrous aggregates of white color and silky luster.

## Characteristics Nepskoeite is a mineral from the halide group, specifically a hydrated magnesium hydroxychloride. It occurs as very small, acicular or bladed crystals, which typically form dense, matted or fibrous aggregates. Individual crystals rarely exceed 1 mm in length. Due to its delicate, fibrous structure, specimens have a characteristic silky luster. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 1.5. It is light, with a density of approximately 2.13 g/cm³. The crystals are flexible and pliable, which is typical for minerals with a fibrous structure. Due to its low hardness, it is extremely delicate and susceptible to mechanical damage. ## Colors and Varieties Nepskoeite is usually white, snow-white, or colorless. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Nepskoe salt deposit, located in the Lower Tunguska River basin in Siberia, Russia. It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 1994.

Properties

Mohs hardness: 1.5
Luster: Silky
Streak: White
Density: 2.13
Cleavage: Perfect on {010}
Fracture: Fibrous
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Nepskoeite can be identified by its characteristic fibrous or acicular form, snow-white color, and silky luster. It is extremely soft and light. A key diagnostic feature is its reaction to water – it is soluble in it. It occurs in the specific environment of salt rocks. ## Distinguishing from Similar Minerals It can be confused with other fibrous secondary minerals found in salt deposits, such as some sulfates (epsomite) or chlorides. Epsomite is also white and fibrous, but has a bitter, salty taste and a different genesis. Final differentiation from the very similar chloride – korshunovskite – requires advanced chemical analyses (XRD, EDS). ## Crystal Forms It forms elongated, acicular or bladed crystals, usually not exceeding 1 mm in length. These crystals combine into dense, tangled aggregates with a felt-like or fibrous structure, as well as small, radial rosettes.

Geological environment

## Genesis Nepskoeite is a secondary mineral, formed as a result of hydrothermal or metasomatic processes affecting rock salt (halite) and sylvite deposits. It forms in veins cutting through salt rocks, often in voids and fissures. ## Mineral Associations It most often co-occurs with minerals typical of salt deposits, such as halite, sylvite, carnallite, bischofite, and the very rare korshunovskite, to which it is closely related chemically and structurally. ## Localities The most important and type locality is the Nepskoe potassium-magnesium salt deposit in the Central Siberian Plateau in Russia. This is the only confirmed and well-documented locality for this mineral in the world.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of nepskoeite primarily depends on the richness and aesthetics of the aggregates. The most prized specimens are those with clearly visible, dense clusters of white, silky fibers, forming a contrasting coating on the salt matrix (halite or sylvite). Due to the microscopic size of the crystals, their individual forms are not a criterion for evaluation. The abundance and purity of the mineral on the host rock are what matter. ## Popular Localities The only source of collector specimens is the type locality – the Nepskoe deposit in Russia. All specimens available on the market come from this single location.

Care and storage

## Cleaning Nepskoeite specimens are extremely delicate and water-soluble. They must absolutely not be cleaned with water. The only permissible method is very careful dust removal using a soft brush or a stream of compressed air from a distance and at low pressure. ## What to Avoid Contact with water, acids, and even humid air should be avoided, as these can cause the mineral to dissolve and be destroyed. The mineral is very soft, so it must be protected from any physical contact, vibrations, and impacts. It should not be heated, as it contains water in its structure. ## Storage Nepskoeite requires storage in dry conditions. It is best kept in a sealed, closed "membrane box" or in a display case away from sources of moisture. Display should only take place in a closed cabinet, at a stable temperature and low humidity.

Sources

IMA Mineral List (CNMNC)