Zincomenite

Chemical formula: Zn₂+Se₄+O₃

Zincobolmenite is a rare zinc selenite, forming small, colorless or white crystals with a vitreous luster, prized by collectors of rare minerals.

## Characteristics Zincobolmenite is a mineral from the selenite group, chemically corresponding to zinc selenite. It occurs as very small, tabular or prismatic crystals, rarely exceeding 1 mm in length. It also forms radial or rosette-like aggregates. It is colorless, white, or pale yellow, often transparent, and exhibits a vitreous luster. ## Physical Properties This mineral has a hardness of approximately 3 on the Mohs scale. It is relatively brittle. Its density is about 4.85 g/cm³. The crystals show perfect cleavage in one direction. ## Colors and Varieties Zincobolmenite is typically colorless to white. Some specimens may have a pale yellow tint, likely due to impurities. No named varieties are distinguished. ## History and Name The name zincobolmenite refers to its chemical composition – the presence of zinc (zincum) and the fact that it is a selenite (menite). It was first described in 1881 based on specimens found in the El Plomo mine in the La Rioja department, Argentina. ## Uses Due to its extreme rarity and small crystal size, zincobolmenite has no industrial applications. It is solely an object of scientific and collector interest.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 4.85
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Zincobolmenite is identified by its crystal habit – small, tabular crystals – and its occurrence in paragenesis with other selenites and selenates. Its location in the oxidation zones of deposits containing selenium and zinc minerals is also characteristic. Due to the small size of the crystals, definitive identification requires advanced analytical methods such as Raman spectroscopy or EDS analysis. ## Distinguishing from Similar Minerals It can be confused with other colorless or white secondary minerals, such as anglesite, cerussite, or other selenites (e.g., chalcomenite). Distinguishing it with the naked eye is practically impossible and requires chemical analysis to confirm the presence of zinc and selenium. ## Crystal Forms Zincobolmenite crystals are usually very small, with a tabular or short-prismatic habit. They often form radial aggregates, rosettes, or fan-shaped clusters on the surface of the host rock.

Geological environment

## Genesis Zincobolmenite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal ore deposits that are rich in selenium and contain zinc minerals, such as sphalerite. It forms under dry and arid conditions as a result of reactions of waters percolating through rocks. ## Mineral Associations It most commonly co-occurs with other rare selenites and selenates, such as chalcomenite, ahlfeldite, olsacherite, as well as with gypsum, barite, and iron oxides (limonite). ## Localities The most important and classic localities for this mineral are in Argentina, in the El Plomo and El Cóndor mines in La Rioja province. It is also known from the Tsumeb mine in Namibia and from several localities in Bolivia (Pacajake mine, Hiaco) and the USA (Gold-Chain mine, Utah).

Rarity

Very rare

For collectors

## Quality Criteria The most prized zincobolmenite specimens are those with well-formed, sharp, and transparent crystals, forming aesthetic groups or rosettes. Contrast with a dark matrix significantly increases the value of the specimen. Due to the small size of the crystals, their quality and form, rather than absolute size, are key. ## Popular Localities Specimens from the Argentine mines of El Cóndor and El Plomo are considered classic and most sought after by collectors. Material from these localities serves as the benchmark for this mineral.

Care and storage

## Cleaning Zincobolmenite specimens should be cleaned with the utmost care, using only compressed air to remove dust. Due to its brittleness and potential solubility, contact with water and any chemicals should be avoided. ## What to Avoid Ultrasonic cleaners, chemical agents, acids, and immersion in water should be absolutely avoided. The mineral is sensitive to changes in temperature and humidity. It should be protected from direct sunlight, which can affect its properties. ## Storage It is recommended to store zincobolmenite specimens under stable conditions, in closed, padded "micromount" boxes, to protect them from mechanical damage, dust, and humidity changes.

Sources

IMA Mineral List (CNMNC)