Gysinite-(La)

Chemical formula: Pb²⁺La(CO₃)₂(OH)·H₂O

A rare lead lanthanum hydroxycarbonate, forming small, prismatic crystals of whitish or yellowish color.

## Characteristics Gysinite-(La) is a rare mineral from the carbonate group, chemically classified as a hydrated lead lanthanum hydroxycarbonate. It occurs as very small, prismatic or tabular crystals, rarely exceeding 0.2 mm in length. These crystals often form rosette-like or spherulitic aggregates. Due to their small size, its visual features are difficult to observe without magnification. ## Physical Properties This mineral has a hardness of approximately 4 on the Mohs scale. It exhibits a vitreous luster. It is a relatively dense mineral due to its lead content, with a calculated density of 4.85 g/cm³. Crystals are transparent to translucent. ## Colors and Varieties Gysinite-(La) is typically colorless, white, pale yellow, or yellowish-green. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral was first described in 1982 by Jacques E. Sarp and Stefan Graeser. Its name honors Bernard Gysin (1894-1966), a professor of mineralogy at the University of Geneva, who studied the Shinkolobwe deposits. The suffix "-(La)" indicates lanthanum as the dominant rare earth element in its structure. It was approved by the IMA in 1981 (IMA1981-059). The type locality is the Shinkolobwe mine in the Democratic Republic of Congo. ## Uses Due to its rarity and microscopic size, gysinite-(La) has no industrial applications. It is solely of interest to collectors specializing in rare minerals (so-called micromounts) and scientists.

Properties

Mohs hardness
3.5-4
Color
Colourless, pale yellow
Luster
Vitreous
Streak
White
Density
5.007
Cleavage
Good on {010}
Fracture
Irregular/Uneven
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification In practice, the identification of gysinite-(La) is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Visually, under microscopic magnification, characteristic small prismatic crystals forming rosette-like aggregates can be observed. It reacts vigorously with acids. ## Distinguishing from Similar Minerals It can be confused with other secondary lead and rare earth carbonates, such as ancylite, bastnäsite, or cerussite, with which it often co-occurs. Definitive differentiation from these minerals requires specialized chemical analysis to determine the composition and the dominant rare earth element. ## Crystal Forms It forms elongated, prismatic crystals with a nearly square cross-section, often terminated by a pyramid. These crystals typically occur as radial or rosette-like aggregates and spherulites.

Geological environment

## Genesis This is a secondary mineral, formed in the oxidation (weathering) zones of uranium, lead, and rare earth ore deposits. It forms as a result of the interaction of carbonate-rich waters with primary minerals containing lead and lanthanum. ## Mineral Associations It co-occurs with other secondary uranium and lead minerals. The most common associations include: uraninite, kasolite, sklodowskite, schoepite, wulfenite, cerussite, bijvoetite-(Y), and malachite. ## Localities The most important and well-documented occurrences of this mineral are the type locality - the Shinkolobwe mine in Haut-Katanga Province (Democratic Republic of Congo) and the uranium mine in Krunkelbach, near Menzenschwand in the Black Forest (Germany).

Rarity

Very rare

For collectors

## Quality Criteria The quality of gysinite-(La) specimens is primarily assessed from the perspective of micromineral collecting (micromounting). The most prized specimens are those with well-formed, sharp crystals forming aesthetic, rosette-like aggregates. The contrast with the rock matrix and the presence of associated minerals are also important. Crystal size, even if sub-millimeter, matters - the larger they are, the more desirable the specimen. ## Popular Localities Undoubtedly, the most valued and classic specimens come from the type locality in the Democratic Republic of Congo (Shinkolobwe). Specimens from the German locality in the Black Forest are also sought after by collectors specializing in systematic and regional minerals.

Care and storage

## Cleaning Specimens should be cleaned with utmost care, using only compressed air to remove dust. Due to the microscopic size of the crystals, any other method, including the use of water or brushes, risks irreversible damage or loss. ## What to Avoid Contact with acids must be absolutely avoided, as they rapidly dissolve the mineral with the release of carbon dioxide. Avoid ultrasonics, steam cleaners, and all chemicals. Protect from high temperatures and mechanical shocks. ## Storage Gysinite-(La) specimens are almost always stored as micromounts in specialized, sealed plastic boxes (micromount boxes), which protect them from dust and mechanical damage. Display should only take place under a microscope.

External references

Sources

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