Strontiopharmacosiderite

Chemical formula: Sr₀.₅Fe₃+₄[(As₅+O₄)₃(OH)₄]·₄H₂O

A rare mineral from the pharmacosiderite group, a hydrated strontium iron arsenate, forming characteristic small cubic crystals.

## Characteristics Strontioparmacosiderite is a mineral belonging to the pharmacosiderite group, being its strontium analogue. It is a hydrated iron and strontium arsenate. It most often forms very small, but well-formed, sharp cubic crystals. Less frequently, it occurs as granular aggregates or coatings. Its crystals, despite their small size, are characterized by a high luster. ## Physical Properties This mineral is relatively soft, with a hardness of 2.5 on the Mohs scale. It exhibits a adamantine luster on crystal faces. It is transparent to translucent. Its density is approximately 2.93 g/cm³. ## Colors and Varieties Strontioparmacosiderite occurs in shades from yellow to yellowish-brown. No color or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition - the presence of strontium (Latin: *strontium*) and its structural similarity to pharmacosiderite. It was described as a new mineral species in 1988 by Donald R. Peacor and Pete J. Dunn based on specimens from the Maria Josefa mine in Spain. ## Applications Due to its rarity and small crystal size, strontioparmacosiderite has no industrial application. It is solely an object of scientific and collector interest.

Properties

Mohs hardness: 2.5
Luster: Adamantine
Streak: White to pale yellow
Density: 2.93
Cleavage: Indistinct on {001}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Cubic

Diagnostic features

## Identification The key diagnostic feature of strontioparmacosiderite is its crystallographic form - it almost always forms perfect, small cubes. Other important features include its yellow color, adamantine luster, and occurrence in the oxidation zones of arsenical deposits. ## Distinguishing from Similar Minerals It is impossible to visually distinguish it from other minerals of the pharmacosiderite group (e.g., potassium pharmacosiderite or natropharmacosiderite) - this requires advanced chemical analyses (e.g., EDS). From other yellow secondary minerals, such as mimetite, it is distinguished by its regular (cubic) crystallographic system. ## Crystal Forms Crystals are almost exclusively in the form of simple cubes, rarely with minor modifications. They occur as single crystals grown on the host rock or form fine, crystalline coatings and druzes.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones (so-called iron caps) of polymetallic ore deposits, mainly as a result of the weathering of primary arsenic minerals (e.g., arsenopyrite) in a strontium-rich environment. ## Mineral Associations It most often co-occurs with other secondary arsenates, such as scorodite, beudantite, olivenite, as well as iron minerals like jarosite, goethite, and limonite. ## Localities The most important localities worldwide include the type locality at the Maria Josefa mine (Rodalquilar, Almería) in Spain. It is also known from Gold Hill in Utah (USA) and the Clara mine in the Black Forest (Germany).

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized specimens are those with sharp, well-formed, lustrous cubes, set on a contrasting rock matrix. The intensity of color and the absence of damage are important. Due to the small size of the crystals, even small aggregates with good development are attractive. ## Popular Localities Specimens from the type locality in Spain and from the German Clara mine are considered classic and are most sought after by collectors specializing in rare minerals or systematics.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water. Avoid strong water jets and ultrasonic cleaners, which can damage delicate crystals. ## What to Avoid The mineral contains arsenic, making it toxic. Wash hands thoroughly after each contact with the specimen. Do not heat it or expose it to acids. Prolonged exposure to intense sunlight may not be advisable. ## Storage It is recommended to store specimens in closed, stable containers or display cases to protect them from dust and mechanical damage. Avoid areas with high humidity.

Sources

IMA Mineral List (CNMNC)