Bariopharmacosiderite
Chemical formula: Ba<sub>0.5</sub>Fe<sup>3+</sup><sub>4</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>(OH)<sub>4</sub>·5H<sub>2</sub>O
Bariopharmacosiderite is a rare barium and iron arsenate, forming characteristic, cubic crystals ranging in color from yellow to greenish-brown.
Description
## Characteristics Bariopharmacosiderite is a hydrated barium and iron arsenate, belonging to the pharmacosiderite group. It is the barium analogue of pharmacosiderite. It most often forms small, well-formed cubic crystals, rarely exceeding 1-2 mm in size. They usually occur as coatings and crystalline druses on the surface of host rocks. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5. It has a vitreous luster, sometimes slightly resinous. It is transparent to translucent. Its density is approximately 2.9 g/cm³. ## Colors and Varieties Bariopharmacosiderite exhibits various shades of yellow, green, and brown. Honey-yellow, amber, greenish-yellow, as well as olive-green and brown crystals are found. No named varieties are distinguished. ## History and Name The mineral was first described in 1966 by Kurt Walenta. Its name refers to its chemical composition – the presence of barium (Latin: *barium*) – and its structural similarity to pharmacosiderite. ## Uses Bariopharmacosiderite has no industrial application. It is of purely scientific and collector's interest, being valued by collectors of rare minerals.
Diagnostic features
## Identification The most important diagnostic feature of bariopharmacosiderite is its crystal habit – it almost always forms distinct, single or twinned cubes. Its characteristic color (yellow, green, brown), low hardness, and occurrence in the oxidation zones of ore deposits are also distinctive. ## Distinguishing from similar minerals It can be confused with pharmacosiderite, from which it can be distinguished by chemical analysis to confirm the presence of barium. It differs from mimetite and pyromorphite by its crystal habit (cubic, not hexagonal) and lower hardness and density. ## Crystal forms Crystals are almost exclusively cubic, sometimes with minor modifications on edges or corners. It occurs as single, overgrown crystals or forms druses and crustal coatings on the host rock.
Geological environment
## Genesis Bariopharmacosiderite is a secondary mineral, formed in the oxidation zones (so-called iron caps) of polymetallic hydrothermal deposits. Its formation is favored by the presence of arsenic minerals (e.g., arsenopyrite) and the presence of barium, most often derived from the weathering of barite. ## Mineral associations It often co-occurs with other minerals from the oxidation zone, such as scorodite, pharmacosiderite, beudantite, olivenite, barite, quartz, and iron oxides (goethite, limonite). ## Localities The most important and classic locality (type locality) is the Clara mine in the Rankach Valley, Black Forest (Germany). It is also known from the Cap Garonne mine in Var (France), from Cornwall (Great Britain), and from several localities in Utah (USA).
Rarity
Very rare
Collector aspects
## Quality criteria The most highly valued specimens are those with sharp, well-formed, vitreous cubes of intense, vivid color (especially honey-yellow and green). The size of the crystals is of great importance – those exceeding 1 mm are already considered large. The attractiveness is enhanced by the placement of crystals on a contrasting rock matrix. ## Popular localities Specimens from the Clara mine in Germany are by far the most sought after by collectors, as this mine yields the world's best crystals of this mineral.
Care and storage
## Cleaning Bariopharmacosiderite specimens are very delicate and chemically sensitive. To remove dust, it is best to use compressed air or a very soft, dry brush. Avoid contact with water, especially acids and detergents. ## What to avoid The mineral contains arsenic, so it is toxic. Avoid inhaling dust and wash hands after any contact with the specimen. It is very soft (prone to scratching) and brittle. Protect it from impacts, high temperatures, and direct sunlight, which can cause color changes. ## Storage It is recommended to store specimens in closed, padded boxes (e.g., "micromount" type), which protects them from mechanical damage and dust. Each specimen should be properly labeled with a toxicity warning.