Shubnikovite

Chemical formula: Ca₂Cu₂+₈(As₅+O₄)₆Cl(OH)·₇H₂O

Shubnikovite is a very rare copper and arsenic mineral, forming blue-green, acicular crystals.

## Characteristics Shubnikovite is a hydrated copper and calcium arsenate of the mixite group. It occurs as fine, acicular or hair-like crystals that form radial or tangled aggregates. Individual crystals are usually too small to be seen with the naked eye, and the material has the appearance of a felted or fibrous mass. ## Physical Properties Shubnikovite crystals are flexible and have a hardness of about 2 on the Mohs scale. The luster is silky to dull, depending on the aggregate form. It is a light mineral, with a density slightly over 3 g/cm³. ## Colors and Varieties This mineral is characterized by a vivid, blue-green or greenish-blue color. No color or commercial varieties are known. ## History and Name Shubnikovite was first described in 2012. Its name honors the Russian crystallographer and physicist Aleksei Vasilievich Shubnikov (1887-1970), founder and first director of the Institute of Crystallography of the Russian Academy of Sciences. It was approved by the International Mineralogical Association (IMA) as a new mineral species. ## Uses Due to its extreme rarity and microscopic crystal size, shubnikovite has no industrial application. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 2
Luster: Silky
Streak: Light green
Density: 3.13
Cleavage: None
Fracture: Uneven
Transparency: Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Field identification of shubnikovite is practically impossible. It requires advanced analytical techniques such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). In a collection, it is recognized by its characteristic blue-green color, fibrous or acicular aggregate appearance, and co-occurrence with other copper arsenates. ## Distinguishing from Similar Minerals Shubnikovite is visually indistinguishable from other minerals of the mixite group, such as mixite itself, agardite, or petersite. It can also be confused with other secondary, acicular copper minerals, such as brochantite or acicular malachite. Certain differentiation is only possible through chemical analysis, which shows the presence of calcium and chlorine in the shubnikovite structure. ## Crystal Forms It forms elongated, acicular or hair-like crystals with a hexagonal cross-section, usually not exceeding 1 mm in length. These crystals combine into radial aggregates, rosettes, spherulites, or tangled, felted masses.

Geological environment

## Genesis Shubnikovite is a secondary mineral, formed in the oxidation (weathering) zones of copper and arsenic ore deposits. It forms as a result of arsenic-rich waters acting on primary copper-bearing minerals, in the presence of calcium and chlorine ions. ## Mineral Associations It most often co-occurs with other secondary copper arsenate minerals, such as olivenite, cornetite, pseudomalachite, as well as tenorite, quartz, and hematite. ## Localities The type locality (place of discovery) is the Zapolyarnoye copper deposit in the northern Urals, Russia. This is the only confirmed occurrence of this mineral in the world.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a shubnikovite specimen is primarily assessed based on the richness and aesthetics of the aggregates on the matrix rock. The most desirable specimens are those with clearly formed, radial aggregates of intense blue-green color, contrasting with the substrate. The size of the specimen and the absence of damage to the delicate fibers also increase its value. ## Popular Localities The only source of specimens is the type locality – the Zapolyarnoye deposit in Russia. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Due to its delicacy and solubility in acids, cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water should be avoided. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is very soft and brittle, susceptible to mechanical damage. It should not be heated or exposed to ultrasound. ## Storage Specimens should be stored in dry conditions, preferably in a closed, transparent display box, to protect them from dust, moisture, and mechanical damage.

Sources

IMA Mineral List (CNMNC)