Barium-zinc alumopharmocosiderite

Chemical formula: (Ba,K)<sub>0.5</sub>(Zn,Cu)<sub>0.5</sub>(Al,Fe)<sub>4</sub>(AsO<sub>4</sub>)<sub>3</sub>·5H<sub>2</sub>O

Barium-zinc alumopharmacosiderite is a rare arsenate from the pharmacosiderite group, distinguished by its complex chemical composition with barium and zinc.

## Characteristics Barium-zinc alumopharmacosiderite is a rare mineral from the pharmacosiderite group, being a hydrated arsenate of aluminum, iron, barium, and zinc. It occurs as very small, cubic crystals, rarely exceeding 0.1 mm in size. These crystals form thin coatings and crusts on the surface of host rocks, often in association with other secondary minerals. ## Physical Properties The crystals exhibit a luster ranging from vitreous to slightly resinous. Due to the microscopic size of the crystals, most physical properties, such as hardness or density, have not been precisely determined. ## Colors and Varieties This mineral is typically colorless to white, sometimes with a pale yellow or greenish tint, depending on impurities and the oxidation state of iron. No distinct varieties have been identified. ## History and Name The mineral's name, approved by the IMA in 2018 (IMA 2018-068), directly refers to its chemical composition. It indicates the dominance of barium and zinc, as well as aluminum (Alumo), and its connection to the structural pharmacosiderite group. It was discovered in the Clara mine in Wolfach, in the German Black Forest.

Properties

Luster
Vitreous
Streak
White
Cleavage
None
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Cubic

Diagnostic features

## Identification Identification of this mineral is possible only through advanced analytical methods, such as Raman spectroscopy or EDS (energy-dispersive spectroscopy) analysis, due to its microscopic size and occurrence in complex parageneses. Visual identification in the field or in a collection is practically impossible. ## Distinguishing from Similar Minerals It can be confused with other minerals from the pharmacosiderite group, such as pharmacosiderite, alumopharmacosiderite, or natropharmacosiderite, which form similar cubic crystals. Differentiation requires confirmation of the presence of barium and zinc in the chemical composition. ## Crystal Forms It forms very small, well-developed cubic crystals, usually grouped into thin coatings and crusts.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones (gossans) of ore deposits rich in arsenic. It crystallizes as a result of the weathering of primary minerals containing arsenic, barium, and zinc in an aluminum-rich environment. ## Mineral Associations It most commonly co-occurs with other rare secondary minerals, such as olivenite, arsenogoyazite, agardite-(Y), cornwallite, goethite, barite, and other minerals from the pharmacosiderite group. ## Localities The only confirmed locality of this mineral in the world (type locality) is the Clara mine, located in the Rankach valley near Wolfach, in the Black Forest, Baden-Württemberg, Germany.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen primarily depends on the richness and visibility of microcrystals on the rock matrix. The most valued samples are those with clearly developed, though still microscopic, cubic crystals, preferably in association with other rare minerals, which increases the scientific and aesthetic value of the specimen. ## Popular Localities The only source of specimens is the Clara mine in Germany, renowned worldwide for providing "micromounts" of exceptional rarity and quality.

Care and storage

## Cleaning Due to the extreme rarity and delicacy of specimens, mechanical cleaning is not recommended. Dust can be removed very carefully with a soft brush or a photographic air blower. Avoid contact with water and any chemical agents. ## What to Avoid Ultrasonic cleaners, steam cleaners, acids, solvents, and sudden temperature changes should be absolutely avoided. The mineral is likely sensitive to moisture and may be damaged by careless handling. ## Storage Specimens should be stored under stable conditions, in sealed collector boxes, away from dust, light, and moisture. It is best to store them in their original container (perky box) to minimize the risk of damage to the delicate crystals.

Sources

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