Mopungite

Chemical formula: NaSb<sup>5+</sup>(OH)<sub>6</sub>

Mopungite is a rare sodium antimony hydroxide from the stottite group, forming microscopic, colorless or white tetragonal crystals.

## Characteristics Mopungite is a hydrated sodium antimony hydroxide, belonging to the stottite subgroup. It occurs as very small, octahedral crystals, rarely exceeding 0.2 mm in size. Most often, it forms granular aggregates or coatings. It is a secondary mineral, formed in the oxidation zones of antimony deposits. ## Physical Properties Mopungite crystals exhibit a hardness of 3 on the Mohs scale. They have a vitreous luster and are opaque. Due to the microscopic size of the crystals, many of its physical properties, such as density or fracture, have not been thoroughly studied. ## Colors and Varieties This mineral is usually colorless, white, or creamy white. No color or commercial varieties have been distinguished. ## History and Name The name mopungite comes from the word "mopung," which means "antimony" in the Sotho language (spoken in Lesotho). This directly refers to the mineral's chemical composition. It was first described in 1982 based on material from the Green Prospect deposit in Churchill County, Nevada (USA). ## Uses Due to its rarity and microscopic specimen sizes, mopungite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and scientists.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
White
Density
0
Fracture
None observed
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identifying mopungite under amateur conditions is practically impossible due to the microscopic size of the crystals. Recognition requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical composition analysis (EDS/WDS). In a collection, it can be identified based on a label from a confirmed locality. ## Distinguishing from Similar Minerals It can be confused with other white secondary antimony minerals, such as valentinite, senarmontite, or stibiconite. Differentiation without specialized equipment is impossible. Mopungite is distinguished by its tetragonal crystal form, whereas senarmontite crystallizes in the isometric system, and valentinite in the orthorhombic system. ## Crystal Forms It forms very small, well-developed octahedral crystals. It occurs as individual crystals or in granular aggregates and coatings on the host rock.

Geological environment

## Genesis Mopungite is a secondary mineral. It forms as a result of low-temperature hydrothermal processes or weathering (oxidation) in antimony ore deposits, especially in the presence of sodium. It forms in rock cavities and fissures. ## Mineral Associations In its type locality (Nevada, USA), it co-occurs with minerals such as stibiconite, tripuhyite, lewisite, and various iron oxides. In other localities, it may be associated with other secondary antimony minerals. ## Localities The most important and type locality is Green Prospect in Nevada, USA. Its presence has also been confirmed in several other places worldwide, including the Cetine mine in Italy (Tuscany), the Clara mine in Germany (Black Forest), and the Murchison Greenstone Belt in South Africa.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the most important criterion is the abundance and size of microscopic crystals on the rock matrix. Specimens with well-formed, sharp octahedra, visible under magnification, are most valued. The contrasting color of the host rock enhances the visual appeal of the specimen. Association with other rare minerals is also important. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality – Green Prospect in Nevada, USA. Specimens from the Cetine mine in Italy are also known and valued in specialized circles.

Care and storage

## Cleaning Mopungite specimens, due to their microscopic nature and fragility, should be cleaned with the utmost care. It is safest to use compressed air to remove dust. Avoid washing in water and using any brushes that could damage the tiny crystals. ## What to Avoid Avoid contact with chemicals, especially acids, which can react with the mineral's components. Do not heat specimens, as this can lead to water loss (dehydration) and structural damage. Protect from moisture and sudden temperature changes. ## Storage It is recommended to store mopungite in stable conditions, in closed, dry containers (e.g., "micromount" type), which protect against dust and mechanical damage. Exposure should be away from direct sunlight and heat sources.

External references

Sources

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