Mandarinoite

Chemical formula: Fe<sup>3+</sup><sub>2</sub>(Se<sup>4+</sup>O<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O

Mandarinoite is a rare, hydrated iron selenite, forming characteristic orange or yellow coatings and microcrystals.

## Characteristics Mandarinoite is a secondary mineral from the selenite group, valued by collectors for its intense, orange-yellow color. It most often occurs as microcrystalline aggregates, coatings, crusts, or as aggregates of prismatic, acicular crystals. Its name refers to its characteristic mandarin color. ## Physical Properties Mandarinoite crystals are very small and brittle. This mineral is characterized by relatively low hardness, approximately 2.5 on the Mohs scale. It has a luster described as resinous to vitreous and is transparent to translucent. Its density is approximately 3.13 g/cm³. ## Colors and Varieties This mineral occurs in shades from bright yellow, through orange-yellow, to mandarin-orange. No named varieties are distinguished, and color variability is slight. ## History and Name The name mandarinoite, given in 1978 by P.J. Dunn, D.R. Peacor, and B.D. Sturman, comes from its characteristic mandarin-orange color. It was discovered in the dumps of the Pacajake mine in the Bolivian department of Potosí. ## Uses Due to its rarity, small crystal size, and brittleness, mandarinoite has no industrial application. It is solely a mineral of scientific and collector's interest.

Properties

Mohs hardness
2.5
Luster
Resinous
Streak
Pale yellow
Density
3.13
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The most important diagnostic feature of mandarinoite is its intense, mandarin-orange color. It occurs as small, prismatic crystals or earthy coatings on the host rock, often in association with other selenites. ## Distinguishing from Similar Minerals It can be confused with other secondary iron minerals of similar color. It is distinguished from chalcomenite by the absence of copper and usually a more orange hue. Identification often requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS), due to the small size of the crystals. ## Crystal Forms It forms elongated, prismatic crystals with a rhombic cross-section, often gathered in radial or chaotic aggregates. It also occurs as very fine-grained, earthy or powdery coatings and crusts.

Geological environment

## Genesis Mandarinoite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits containing selenium minerals. It forms under low temperature and pressure conditions as a result of the oxidation of primary selenides, most often in the presence of iron minerals. ## Mineral Associations It co-occurs with other rare selenites, such as chalcomenite, ahlfeldite, penroseite, as well as with quartz, barite, hematite, and goethite. ## Localities The most important and classic locality for this mineral is the Pacajake mine in Bolivia. It is also known from the El Dragón mine (also in Bolivia), Tsumeb in Namibia, the De Lamar mine in Idaho (USA), and several locations in Argentina (including Sierra de Cacheuta).

Rarity

Very rare

For collectors

## Quality Criteria The most prized mandarinoite specimens are those with well-formed, lustrous crystals of intense orange color, forming rich aggregates on a contrasting host rock. Due to the microscopic nature of most crystals, specimens with sharp crystals visible to the naked eye are exceptionally sought after. Contrast with associated minerals is also important. ## Popular Localities The best quality specimens, with relatively large and well-formed crystals, come from the Bolivian mines of Pacajake and El Dragón. These are considered classics for this mineral.

Care and storage

## Cleaning Mandarinoite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly risky. If necessary, compressed air (from a safe distance) can be used to remove dust. Any contact with water, which can damage or dissolve the mineral, should be avoided. ## What to Avoid Contact with water and other liquids, including cleaning agents, must be strictly avoided. The mineral is very soft and brittle, susceptible to scratches and mechanical damage. It should be protected from high temperatures and direct sunlight, which can cause dehydration and color change. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "micromount" type) that protect against dust, moisture, and physical damage. Display should be in a dry place, away from sources of vibration and direct light.

Sources

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