Stavelotite-(La)

Chemical formula: La₃Mn₂+₃Cu₂+(Mn₃+,Fe₃+,Mn₄+)₂₆(Si₂O₇)₆O₃₀

Stavelotite-(La) is an extremely rare mineral with a complex composition, discovered in Belgium, forming microscopic, black crystals.

## Characteristics Stavelotite-(La) is a silicate mineral belonging to the ardennite group. It occurs as very small, tabular or prismatic crystals, reaching up to 0.2 mm in size. It typically forms radial aggregates. It is black and opaque, with a metallic luster. ## Physical properties Due to the microscopic size of the crystals, many physical properties have not been precisely determined. Hardness is estimated at approximately 6 on the Mohs scale. The density calculated based on the formula and unit cell parameters is 4.43 g/cm³. ## History and name The mineral was discovered in a quarry in the Salm River valley, near the town of Stavelot in Belgium, from which its name is derived. The "-(La)" suffix indicates lanthanum as the dominant rare earth element in its structure. It was approved by the International Mineralogical Association (IMA) in 2018 under number 2018-028. It was described by Frédéric Hatert and collaborators. ## Applications Stavelotite-(La) has no industrial applications. Its significance is purely scientific and as a collector's item, as a unique and newly discovered mineral.

Properties

Mohs hardness: 6
Luster: Metallic
Streak: Black
Density: 4.43
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of stavelotite-(La) is impossible without advanced analytical methods. It requires chemical analysis (EDS) to confirm the presence of lanthanum, manganese, copper, and silicon in appropriate proportions, as well as X-ray diffraction (XRD) to determine the crystal structure. Visually, it is simply a "black mineral" in the form of microscopic crystals. ## Distinguishing from similar minerals It can be confused with many other black, fine-grained manganese minerals, such as piemontite, ardennite-(As), or hollandite, which occur in similar geological environments. Definitive differentiation is only possible through specialized studies. ## Crystal forms It forms very small, tabular crystals with a hexagonal outline, elongated along the [001] axis. They often occur as radial or randomly oriented aggregates on the rock surface.

Geological environment

## Genesis Stavelotite-(La) forms under low-grade metamorphic conditions. It occurs in quartz veins cutting phyllitic and quartzitic rocks. Its formation is associated with hydrothermal mobilization and concentration of rare earth elements (mainly lanthanum), manganese, and copper. ## Mineral associations This mineral co-occurs with quartz, ardennite-(As), andalusite, pyroxmangite, spessartine, hematite, and hollandite. ## Localities The only confirmed occurrence worldwide (type locality) is a quarry in the Salm River valley, in the Stavelot Massif, Liège Province, Belgium.

Rarity

Extremely rare

For collectors

## Quality criteria As a "micromount" mineral, its collector's value depends on the abundance and development of microscopic crystals on the matrix. The most desirable specimens are those with distinct, radial aggregates of well-formed crystals, contrasting with a quartz background. Precise documentation and analytical confirmation of the mineral's identity are crucial. ## Popular localities The only source of specimens is the type locality in Belgium. Material from this location is extremely limited and primarily available in specialized collections and research institutions.

Care and storage

## Cleaning Stavelotite-(La) specimens are extremely small and delicate, embedded in a rock matrix. Mechanical or chemical cleaning is not recommended to avoid damaging or losing the microscopic crystals. If necessary, compressed air (from a safe distance) can be used to remove dust. ## What to avoid Avoid contact with any chemicals, acids, and ultrasonic cleaners. Sudden temperature changes can be harmful to the host rock. ## Storage Specimens should be stored under stable conditions, in a closed "micromount" box, to protect them from dust, moisture, and mechanical damage. A label with precise locality information is crucial for the specimen's value.

Sources

IMA Mineral List (CNMNC)