Manganarsite

Chemical formula: Mn<sup>2+</sup><sub>3</sub>As<sup>3+</sup><sub>2</sub>O<sub>4</sub>(OH)<sub>4</sub>

Manganarsite is a rare manganese arsenite, forming small, hexagonal, reddish-brown crystals, found in manganese deposits.

## Characteristics Manganarsite is a very rare mineral from the arsenite group, chemically a basic manganese arsenite. It occurs as very small, tabular or platy crystals with a hexagonal outline, usually not exceeding 1 mm. It also forms rosette aggregates and thin coatings. Its characteristic feature is an intense, reddish-brown to orange-brown color. ## Physical Properties This mineral is characterized by a hardness of approximately 3 on the Mohs scale. It has a luster described as vitreous to greasy. It is translucent. Due to the small size of the crystals, precise determination of density is difficult, but the calculated value is approximately 3.91 g/cm³. ## Colors and Varieties Typical colors of manganarsite are reddish-brown, orange-brown, and brown. No varieties have been distinguished. ## History and Name The mineral's name, given in 1984 by Pete J. Dunn, Donald R. Peacor, and Shu-Chun Su, directly refers to its chemical composition – the content of manganese (mangan) and arsenic (ars). It was discovered in the Långban mine in Filipstad municipality, Värmland region, Sweden, which is its type locality. ## Uses Manganarsite has no industrial application. It is of purely scientific and collector's interest as a very rare mineral.

Properties

Mohs hardness
3
Luster
Vitreous to Greasy
Streak
Brown
Density
3.91
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Amateur identification of manganarsite is practically impossible due to the microscopic size of its crystals and its similarity to other manganese minerals. Identification relies on its characteristic reddish-brown color, the hexagonal outline of small crystals, and its co-occurrence with other rare minerals from the Långban deposit. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS). ## Distinguishing from similar minerals It can be confused with other rare arsenites and manganese oxides, such as hausmannite, pyrochroite, or magnussonite, which occur in the same environment. Distinguishing it from these requires specialized laboratory tests. ## Crystal forms Manganarsite forms very small, thin, tabular crystals with a hexagonal outline. These crystals often group into rosette or radial aggregates. It also occurs as thin coatings and efflorescences on other minerals.

Geological environment

## Genesis Manganarsite is a mineral of metamorphic origin. It forms as a result of the metamorphism of iron and manganese ore deposits. It occurs in skarns and metamorphic rocks rich in manganese. ## Mineral associations This mineral co-occurs with other, often rare, minerals characteristic of metamorphosed manganese deposits. In its type locality (Långban), it was found in association with magnussonite, hausmannite, katoptrite, tephroite, pyrochroite, barite, and calcite. ## Localities The only confirmed and well-documented occurrence of manganarsite in the world is the Långban mine in the Värmland region, Sweden. This is its type locality and the source of practically all known specimens.

Rarity

Very rare

For collectors

## Quality criteria The quality of a manganarsite specimen is determined by the richness and visibility of the crystals on the rock matrix. Specimens with clearly formed, though still microscopic, rosette aggregates of an intense, reddish-brown color are most valued. Contrast with associated minerals is also important. ## Popular localities The only source of collector's specimens is the historic Långban mine in Sweden. Specimens from this locality are highly sought after by collectors specializing in rare minerals or systematic minerals.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its rarity and potential fragility, contact with water and any chemical agents should be avoided. ## What to avoid Contact with acids and other chemicals that may damage the mineral should be strictly avoided. It should be protected from ultrasound, high temperatures, and sudden temperature changes. Due to its arsenic content, inhaling dust should be avoided, and hands should be washed after contact with the mineral. ## Storage Manganarsite specimens should be stored in stable conditions, in closed containers or display cases, away from dust, moisture, and direct sunlight. It is best to store it in a dedicated specimen box to avoid abrasions and mechanical damage.

Sources

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