Stibiosegnitite

Chemical formula: Pb₂+(Fe₃+₂.₅Sb₅+₀.₅)(As₅+O₄)₂(OH)₆

Stibiosegnitite is a very rare lead, iron, and antimony arsenate, forming microscopic, yellowish coatings and aggregates.

## Characteristics Stibiosegnitite is a mineral from the alunite supergroup, being a hydrated lead, iron, and antimony arsenate. It most commonly occurs as earthy, porous, or spongy masses, as well as thin coatings and crusts. It rarely forms visible crystals, which are microscopic, sharply terminated rhombohedra not exceeding 20 micrometers in size. Typically, specimens appear as a dull, dusty coating on the host rock. ## Physical Properties The luster of stibiosegnitite is predominantly earthy or dull. The mineral is translucent to opaque. Due to its microcrystalline nature and occurrence as coatings, its hardness has not been precisely determined. The density calculated based on the chemical formula and unit cell parameters is approximately 4.55 g/cm³. ## Colors and Varieties The mineral ranges in color from pale yellow to yellowish-brown. No color varieties or commercial varieties are distinguished. ## History and Name Stibiosegnitite was officially described as a new mineral in 2009 by Peter Elliott and co-workers. Its name refers to its chemical composition – the presence of antimony (Latin: *stibium*) – and its structural and chemical similarity to segnitite. The type locality (discovery site) is Kintore Opencut in Broken Hill, New South Wales, Australia. ## Applications Due to its extreme rarity and occurrence in small aggregates, stibiosegnitite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals.

Properties

Luster: Earthy
Streak: Pale yellow
Density: 4.55 (obliczona)
Cleavage: None
Fracture: Earthy
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identification of stibiosegnitite under amateur conditions is practically impossible. Its appearance – yellow, earthy coatings – is common to many secondary minerals. Reliable identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/SEM), to confirm the presence of lead, iron, arsenic, and antimony, which is key to this mineral. ## Distinguishing from Similar Minerals Stibiosegnitite is visually indistinguishable from segnitite, with which it often co-occurs. The difference lies in the antimony content, which is absent or present in trace amounts in segnitite. It can also be confused with other minerals from the beudantite group (e.g., beudantite itself, corkite), as well as other yellow arsenates, such as mimetite or pharmacosiderite. Differentiation always requires chemical analysis. ## Crystal Forms Crystals are microscopic, with a rhombohedral habit. Most often, it forms earthy, porous, and dusty aggregates, as well as thin crusts and coatings on other minerals.

Geological environment

## Genesis Stibiosegnitite is a secondary mineral, formed in the oxidation (weathering) zones of polymetallic (Pb-Zn-Ag) ore deposits of hydrothermal genesis. It forms as a result of the alteration of primary minerals containing lead, iron, arsenic, and antimony under conditions of low temperatures and pressures. ## Mineral Associations At the type locality (Broken Hill), stibiosegnitite co-occurs with segnitite, beudantite, corkite, hinsdalite, plumbogummite, pyromorphite, mimetite, scholzite, and goethite. ## Localities This is a very rare mineral, known from only a few localities worldwide. The most important locality is Kintore Opencut in Broken Hill (Australia), which is its type locality. It has also been confirmed in the famous Tsumeb mine in Namibia and several other localities known for the occurrence of rare secondary minerals.

Rarity

Very rare

For collectors

## Quality Criteria The quality of stibiosegnitite specimens is assessed primarily in terms of scientific and documentary value, rather than aesthetic value. Micromount specimens from the type locality (Broken Hill) are most highly prized. Key criteria include the richness of the coating on the matrix, analytically confirmed mineral identity, and co-occurrence with other rare arsenates. Visible crystals, even under high magnification, significantly increase the value of the specimen. ## Popular Localities By far the most sought-after and valuable specimens come from Kintore Opencut in Broken Hill, Australia. This locality is the source of the best-formed and most studied stibiosegnitite samples.

Care and storage

## Cleaning Stibiosegnitite specimens are very delicate and fragile. They should be cleaned with the utmost care, preferably using compressed air to remove dust. Due to the porous nature of the aggregates, contact with water should be avoided, as it can be difficult to remove and may contain impurities. If necessary, distilled water and a very soft brush can be used, followed by thorough drying of the specimen. ## What to Avoid Ultrasonic cleaners, strong water jets, and all chemical agents, especially acids, which will destroy the mineral, must be absolutely avoided. As a lead arsenate, the mineral is toxic – avoid inhaling dust and wash hands after any contact with the specimen. ## Storage It is recommended to store specimens in closed, stable containers (e.g., micromount type) to protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and extreme temperatures.

Sources

IMA Mineral List (CNMNC)