Jarosewichite

Chemical formula: Mn³⁺Mn²⁺₃As⁵⁺O₄(OH)₆

Jarosewichite is a rare manganese arsenate with a characteristic dark reddish-brown color, occurring in radial aggregates.

## Characteristics Jarosewichite is a rare mineral from the chlorophoenicite group, being a basic manganese arsenate. It forms characteristic radial or spherulitic aggregates, composed of small, bladed or acicular crystals. Its typical specimens have an intense, dark reddish-brown color and exhibit translucency at the edges. ## Physical Properties This mineral is characterized by a hardness of 4 on the Mohs scale and a density of 3.66 g/cm³. It is translucent, and its luster is described as vitreous to resinous. The fracture is uneven. ## Colors and Varieties Jarosewichite occurs in a uniform, dark reddish-brown color. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered and described in 1982. Its name honors Eugene "Gene" Jarosewich (1926-2007), an American chemist and curator of the meteorite collection at the Smithsonian Institution, who developed many standards for electron microprobe analysis. ## Applications Due to its rarity and small crystal size, jarosewichite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientific institutions.

Properties

Mohs hardness: 4
Luster: Vitreous to Resinous
Streak: Reddish orange
Density: 3.66
Fracture: Irregular/Uneven
Transparency: Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Key diagnostic features of jarosewichite include its dark reddish-brown color, orange-red streak, and characteristic occurrence in radial or spherulitic aggregates. Its association with other manganese minerals from Franklin is also an important clue. ## Differentiation from Similar Minerals It can be confused with other rare manganese arsenates from Franklin, such as magnussonite or chlorophoenicite. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Crystal Forms Jarosewichite forms radial aggregates of small, bladed crystals, which can reach up to 2 mm in length. It is less commonly found in spherulitic clusters.

Geological environment

## Genesis It is a secondary mineral, formed as a result of hydrothermal or metamorphic processes within metamorphosed zinc, iron, and manganese ore deposits. It occurs in fissures and small rock cavities. ## Mineral Associations This mineral co-occurs with other minerals typical of the Franklin deposit, such as franklinite, willemite, zincite, andradite, magnussonite, chlorophoenicite, holdenite, and eveite. ## Localities The only confirmed locality of jarosewichite in the world is its type locality - Buckwheat Pit within the Franklin Mine, Sussex County, New Jersey, USA. This is one of the most mineralogically diverse places on Earth.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those that show well-formed, radial aggregates on a contrasting matrix. The intensity of the color and the size of the aggregates are important. Specimens with visible, well-defined crystals are particularly sought after. ## Popular Localities The only source of jarosewichite specimens is the historic Franklin Mine in New Jersey, USA. All materials available on the collector's market come from this single, classic locality.

Care and storage

## Cleaning Cleaning is recommended only with a soft brush to remove dust. Water and chemical agents should be avoided, as the mineral may be sensitive to them. ## What to Avoid Contact with acids and other chemicals should be avoided. Due to its relatively low hardness, the mineral is susceptible to scratches and mechanical damage. It should be protected from ultrasound and sudden temperature changes. ## Storage Jarosewichite specimens are best stored in separate, padded collector boxes to prevent abrasions and damage. They should be protected from dust and moisture.