Arseniopleite

Chemical formula: NaCaMn₂+Mn₂+₂(As₅+O₄)₃

Arseniopleite is a rare sodium, calcium, and manganese arsenate, forming characteristic, tabular crystals of dark red color and vitreous luster.

## Characteristics Arseniopleite is a complex arsenate belonging to the alluaudite group, characterized by a rich, dark red to reddish-brown color. It occurs as thick, tabular crystals, often forming rosette-like or radial aggregates. The crystals can be partially or completely translucent and exhibit a vitreous luster, and a greasy luster on fracture surfaces. ## Physical Properties This mineral has a hardness of about 3.5 on the Mohs scale, making it relatively soft. Its density is significant, approximately 4.16 g/cm³. The crystals show distinct cleavage in one direction. ## Colors and Varieties The predominant color of arseniopleite is dark red to reddish-brown. No named varieties are distinguished. ## History and Name The mineral's name, given in 1888 by Lars Johan Igelström, refers to its chemical composition – the presence of arsenic (arsenio-) and the Greek word "pleion" meaning "more", which referred to a higher manganese content compared to the similar mineral karynite. It was discovered in the Sjö mine in the Grythyttan region, Västmanland, Sweden. ## Uses Arseniopleite has no industrial application. It is solely a mineral of scientific and collector's interest.

Properties

Mohs hardness: 3.5
Luster: Vitreous, Greasy
Streak: Red-brown
Density: 4.16
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Arseniopleite can be identified by its characteristic dark red color, tabular crystal habit, relatively high density, and occurrence in a specific geological environment – metamorphic manganese and iron ore deposits. ## Distinguishing from Similar Minerals It can be confused with other manganese arsenates, such as sarkinite, brandtite, or magnussonite. Differentiation often requires chemical or crystallographic analysis. However, its habit and color are quite characteristic. ## Crystal Forms Crystals are usually thick tabular, with a hexagonal or rhombic outline. They often form radial or rosette-like aggregates and granular masses.

Geological environment

## Genesis Arseniopleite is a mineral of metamorphic origin. It forms in iron and manganese ore deposits that have undergone regional or contact metamorphism, often in the presence of carbonate rocks (skarns). ## Mineral Associations It often co-occurs with other manganese and arsenic minerals, such as hausmannite, magnussonite, sarkinite, brandtite, berzeliite, tephroite, as well as calcite and barite. ## Localities The most important and classic localities for this mineral are in Sweden, in historical ore mines in the Bergslagen region, such as Långban, Sjö, and Nordmark. Outside Sweden, its occurrence has been reported in the Sterling Hill mine in New Jersey, USA.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals of intense red color and good luster. Large, radial aggregates and aesthetic contrasts with associated minerals, e.g., white calcite, enhance their attractiveness. ## Popular Localities By far the most sought-after arseniopleite specimens come from classic Swedish localities, especially Långban, which is famous for supplying the world's best crystals of this mineral.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the arsenic content, inhalation of dust should be avoided. After contact with the mineral, it is recommended to wash hands. ## What to Avoid Avoid contact with water and chemicals, which can damage the crystal surfaces. The mineral is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or subjected to ultrasound. ## Storage Arseniopleite specimens are best stored in separate, padded collector boxes to prevent abrasion and mechanical damage. It should be kept away from moisture and direct sunlight.

Sources

IMA Mineral List (CNMNC)