Dixenite

Chemical formula: Cu<sup>1+</sup>Mn<sup>2+</sup><sub>14</sub>Fe<sup>3+</sup>(As<sup>3+</sup>O<sub>3</sub>)<sub>5</sub>(SiO<sub>4</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)(OH)<sub>6</sub>

A rare manganese arsenate-silicate, forming characteristic, hexagonal crystals of reddish-brown color and resinous luster.

## Characteristics Dixenite is a complex manganese, copper, and iron arsenate-silicate, belonging to the group of rare minerals. It occurs as small, but well-formed, hexagonal crystals with a tabular or thick-tabular habit. It often forms rosette-like or fan-shaped aggregates. Its most characteristic features are its intense, dark reddish-brown color and strong, resinous luster, which on some surfaces can transition to greasy or almost metallic. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3-4. It is quite brittle, and its density is high, approximately 4.2 g/cm³. Crystals are usually translucent at the edges and opaque in thicker fragments. Luster is one of its main diagnostic features – strongly resinous to greasy. ## Colors and Varieties Dixenite occurs in a uniform range of colors, from dark brown to reddish-brown. Thinner fragments or crystal edges may show a reddish tint. No named varieties are distinguished. ## History and Name The mineral's name comes from the Greek word "δίξενος" (dixenos), meaning "two kinds of guests," which alludes to the presence of two different anions in its chemical structure: (AsO₃) and (SiO₄). It was first described in 1920 by G. Flink based on specimens found in the Långban mine in Sweden. ## Uses Due to its extreme rarity, dixenite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from the Långban skarns.

Properties

Mohs hardness
3-4
Luster
Resinous
Streak
Reddish-brown
Density
4.2
Cleavage
Good on {0001}
Fracture
Uneven to conchoidal
Transparency
Translucent to opaque
Crystal system
Trigonal

Diagnostic features

## Identification Key diagnostic features of dixenite include its hexagonal crystal habit, often in the form of tablets or rosettes, intense reddish-brown color, and very characteristic, strong resinous luster. Low hardness (3-4) is also helpful in identification. ## Distinguishing from Similar Minerals Dixenite can be confused with other rare minerals from Långban, such as hematolite or magnussonite. Hematolite has a similar color but forms trigonal crystals, often with a different habit. Magnussonite crystallizes in the isometric system and has a different chemical composition. Precise differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Dixenite crystallizes in the trigonal system, forming pseudohexagonal, thick-tabular crystals. Crystals are often aggregated into fan-shaped, rosette-like, or radial forms. Single, well-formed crystals are less common.

Geological environment

## Genesis Dixenite is a mineral of metamorphic origin. It forms in iron and manganese ore deposits that have undergone contact metamorphism. It occurs in skarns and metamorphosed carbonate rocks rich in manganese. ## Mineral Associations This mineral co-occurs with other rare minerals typical of the Långban deposit, such as calcite, baryte, hematolite, magnussonite, richterite, phlogopite, hausmannite, and tephroite. ## Localities The only confirmed and classic locality for dixenite worldwide is the Långban mine in the Värmland region, Sweden. This is its type locality. The second known occurrence is the Sterling Hill mine in Ogdensburg, New Jersey, USA, where it also occurs in metamorphosed zinc, iron, and manganese ore deposits.

Rarity

Very rare

For collectors

## Quality Criteria The most prized dixenite specimens are those with sharp, well-formed crystals of intense, reddish-brown color and strong luster. Large, single crystals or aesthetic, rosette-like aggregates on a contrasting matrix (e.g., on white calcite) command the highest prices. Association with other rare minerals from Långban or Sterling Hill is also important. ## Popular Localities By far the most sought-after and classic specimens come from the type locality – the Långban mine in Sweden. Specimens from Sterling Hill in the USA are also valued, but those from Sweden are considered historically most important and are the standard for this species.

Care and storage

## Cleaning Dixenite specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to the presence of arsenic and its brittleness, avoid washing in water, and especially in chemical solutions. If a liquid is necessary, isopropyl alcohol applied to a cotton swab is recommended, with utmost caution. ## What to Avoid Contact with acids and other chemicals that can damage the mineral must be strictly avoided. Dixenite is brittle, so it must be protected from impacts and falls. It should not be heated or subjected to ultrasound. Due to its arsenic content, avoid inhaling dust and wash hands after each contact with the specimen. ## Storage Dixenite specimens are best stored in closed, padded collector boxes to protect them from mechanical damage and dust. They should be kept away from minerals that might react with them. Storage in a dry place, away from direct sunlight, is recommended.

Sources

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