Gungerite

Chemical formula: TlAs₅Sb₄S₁₃

Gungeryite is a very rare thallium, arsenic, and antimony sulfosalt, forming tiny, acicular crystals with a metallic luster.

## Characteristics Gungeryite is a very rare mineral from the sulfosalt group, chemically a complex sulfide of thallium, arsenic, and antimony. It occurs as very small, acicular or hair-like crystals, which can form tangled aggregates. Individual crystals are flexible and rarely exceed 1 mm in length. Due to its size and rarity, it is a mineral known mainly to specialists and advanced collectors. ## Physical Properties Gungeryite crystals exhibit a strong, metallic luster. They are opaque. Due to the small size of the crystals, precise determination of many physical properties, such as hardness or density, is difficult. The density calculated based on the chemical formula and unit cell parameters is 5.15 g/cm³. ## Colors and Varieties This mineral has a dark gray to black color, with a reddish-brown streak. No varieties have been distinguished. ## History and Name The name gungeryite comes from its discovery locality – the Gung (or Gunge) deposit in the Pish district of Iran. It was officially recognized as a new mineral by the International Mineralogical Association (IMA) in 2018 (IMA2018-031). It was described by a team of mineralogists, including Werner H. Paulus and Norbert Stüßer.

Properties

Luster: Metallic
Streak: Reddish-brown
Density: 5.15
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Amateur identification of gungeryite is practically impossible. It requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS) to confirm the chemical composition (presence of Tl, As, and Sb) and X-ray diffraction (XRD) to determine the crystal structure. Visually, it can be suspected based on its form (small, acicular, flexible crystals), metallic luster, and co-occurrence with other sulfosalts in a specific geological environment. ## Distinguishing from Similar Minerals It can be confused with many other acicular sulfosalts, such as jamesonite, boulangerite, zinkenite, or other rare thallium sulfosalts (e.g., pierrotite, parapierrotite). Definitive differentiation is possible only through chemical and structural analysis. ## Crystal Forms Gungeryite forms very small, elongated, acicular or hair-like crystals, often grouped into tangled or radial aggregates. The crystals are flexible.

Geological environment

## Genesis Gungeryite is a low-temperature hydrothermal mineral. It forms in polymetallic deposits where solutions rich in thallium, arsenic, and antimony are present. ## Mineral Associations In its type locality (Gung deposit in Iran), its co-occurrence with other sulfosalts such as pierrotite, parapierrotite, as well as orpiment and realgar, has been observed. ## Localities The only confirmed locality for gungeryite worldwide is its type locality: the Gung deposit, located in the Pish district, West Azerbaijan Province, Iran.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the value of a specimen is primarily determined by the abundance and quality of crystals visible under a microscope. The most desirable specimens are those with dense, well-formed aggregates of acicular crystals, clearly contrasting with the host rock. Precise confirmation of the mineral's identification using analytical methods is also important. ## Popular Localities The only source of gungeryite specimens is its discovery locality in Iran, which makes them extremely rare and available only on a highly specialized collector's market.

Care and storage

## Cleaning Due to the extreme delicacy and small size of the crystals, mechanical cleaning is not recommended. If necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water and any chemicals. ## What to Avoid The mineral is very sensitive to mechanical damage – avoid touching, vibrations, and shocks. As a sulfide containing toxic elements (thallium, arsenic), it should be stored away from moisture, acids, and environments that could cause its chemical decomposition. Avoid exposure to high temperatures. ## Storage Gungeryite specimens should be stored exclusively in stable, sealed "micromount" containers to protect them from physical damage and dust. The container should be clearly labeled due to the mineral's toxicity. Storage in a dry place is recommended.

Sources

IMA Mineral List (CNMNC)