Sundiusite

Chemical formula: Pb₂+₁₀(S₆+O₄)O₈Cl₂

Sundiusite is a rare lead sulfate, oxide, and chloride, forming small, tabular crystals with a pearly or vitreous luster.

## Characteristics Sundiusite is a complex lead sulfate, oxide, and chloride. It occurs as very small, thin, tabular crystals, often forming rosette-like or bladed aggregates. Individual crystals rarely exceed 0.5 mm. Due to its size, its visual features are difficult to observe without magnification. ## Physical Properties Sundiusite crystals are flexible and pliable. The mineral is characterized by a pearly luster on cleavage surfaces and a vitreous luster on other faces. It is transparent to translucent. Its hardness and density have not been precisely determined due to the small size of the samples. ## Colors and Varieties Sundiusite is colorless, sometimes with a pale yellow or greenish tint. No varieties have been distinguished. ## History and Name The mineral was named in honor of Nils Gustaf Sundius (1886-1976), a Swedish mineralogist and petrologist who worked at the Swedish Museum of Natural History. It was approved as a new mineral species by the IMA in 1980, and its description was published in 1982. The type locality is the old mine dumps at Långban, Sweden. ## Uses Sundiusite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness: 2.5
Luster: Pearly, Vitreous
Streak: White
Density: 7.03
Cleavage: Perfect on {001}
Fracture: Micaceous
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of sundiusite requires specialized analytical equipment, such as energy-dispersive X-ray spectroscopy (EDS/EDX) or X-ray diffraction (XRD), due to its co-occurrence with other rare lead minerals of similar appearance. Visually, it is characterized by thin, colorless tabular forms with a pearly luster, often in rosette-like aggregates. ## Distinguishing from Similar Minerals It can be confused with other secondary, colorless lead minerals from Långban, such as georgiadesite, kombatite, or ekdemite. Definitive differentiation is almost exclusively possible using analytical methods. Compared to georgiadesite, sundiusite forms more defined, bladed crystals. ## Crystal Forms It forms thin, tabular crystals with a hexagonal outline, elongated in one direction. These crystals often combine into bladed, fan-shaped, or rosette-like aggregates.

Geological environment

## Genesis Sundiusite is a secondary mineral that formed as a result of reactions occurring within metamorphic iron and manganese ore deposits. Its crystallization took place in fissures and voids in skarns, in an environment rich in lead, chlorine, and sulfates. ## Mineral Associations It most commonly co-occurs with magnetite, hematite, calcite, and other rare lead minerals such as georgiadesite, kombatite, ekdemite, sphalerite, pyrochroite, and hausmannite. ## Localities The only confirmed and described locality for sundiusite in the world is the historical iron and manganese ore deposits at Långban, in the Värmland region of Sweden.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a sundiusite specimen depends on the size and development of the crystals and the richness of the aggregates on the rock matrix. The most prized specimens are those with clearly formed, rosette-like clusters of transparent crystals, contrasting with a dark matrix. Due to the microscopic nature of the mineral, the aesthetics of the entire micromount are crucial. ## Popular Localities All known collector specimens come from a single locality in the world: Långban, Sweden. This is the classic and only locality for this mineral.

Care and storage

## Cleaning Sundiusite specimens are extremely delicate and small. Any mechanical cleaning should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove dust. ## What to Avoid Avoid contact with water, chemicals, acids, and ultrasound. The crystals are very soft and brittle, and also sensitive to temperature changes. Specimens should not be exposed to direct sunlight. ## Storage It is recommended to store specimens exclusively in specialized micromount boxes to protect delicate crystals from mechanical damage, dust, and moisture.

Sources

IMA Mineral List (CNMNC)