Sklodowskite

Chemical formula: Mg(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(SiO<sub>3</sub>OH)<sub>2</sub>·6H<sub>2</sub>O

Sklodowskite is a magnesium uranyl silicate, forming characteristic, acicular crystals of an intensely yellow or greenish-yellow color.

## Characteristics Sklodowskite is a secondary mineral from the uranyl silicate group, valued by collectors for its intense, vivid color and attractive forms of occurrence. It forms aggregates in the shape of radial clusters, crusts, as well as well-formed, acicular or hair-like crystals. Individual crystals are usually very small and delicate, rarely exceeding a few millimeters in length, but their dense clusters can cover significant rock surfaces. ## Physical Properties This mineral is relatively soft, with a hardness of about 2-3 on the Mohs scale. Its crystals exhibit a vitreous to silky luster, especially in the case of fibrous aggregates. It is transparent to translucent. The density of sklodowskite is approximately 3.54 g/cm³. It is strongly radioactive due to its high uranium content. ## Colors and Varieties Sklodowskite occurs in characteristic, vivid shades of yellow – from lemon-yellow, through canary-yellow, to greenish-yellow. Color is one of its main visual attributes. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1924 by the Belgian mineralogist Alfred Schoep. He named it in honor of Marie Skłodowska-Curie (1867-1934), a Polish-French scientist and pioneer in radioactivity research, in recognition of her fundamental discoveries concerning radium and polonium. The type locality, from which the first described samples originated, is the Shinkolobwe mine in the Democratic Republic of Congo. ## Uses Due to its rarity and form of occurrence, sklodowskite has no industrial application. It is of purely scientific and collector's interest, being a sought-after uranium mineral.

Properties

Mohs hardness
2-3
Luster
Vitreous, Silky
Streak
Yellowish white
Density
3.54
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of sklodowskite include its intense, lemon-yellow to greenish-yellow color, acicular or hair-like crystal form creating radial aggregates, and strong radioactivity. It often occurs in the oxidation zones of uranium deposits. Under shortwave UV light, it exhibits weak, green fluorescence. ## Distinguishing from Similar Minerals Sklodowskite is sometimes confused with other secondary uranium minerals, especially uranophane. Uranophane (calcium uranyl silicate) has a very similar appearance and properties, and their definitive distinction often requires chemical analysis (EDS) to determine the presence of magnesium (in sklodowskite) or calcium (in uranophane). Uranophane more often forms compact and dull aggregates, while sklodowskite more frequently forms lustrous, acicular aggregates. ## Crystal Forms Sklodowskite crystals are monoclinic, but exhibit a pseudo-orthorhombic habit. They are strongly elongated, acicular, hair-like, or bladed. They typically form radial, stellate, or fan-shaped aggregates, as well as dense, felted clusters and crusts on the host rock.

Geological environment

## Genesis Sklodowskite is a secondary mineral, forming in the oxidation (weathering) zones of uraninite and other primary uranium minerals. It forms as a result of the action of silica- and magnesium-rich waters on uranium ores. It is a product of relatively late stages of hydrothermal alteration at low temperatures. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associations include uranophane, kasolite, torbernite, curite, soddyite, as well as primary uraninite. It can also occur in association with quartz, feldspars, and clay minerals. ## Localities The most important and historical locality for sklodowskite, from which the best specimens originate, is the Shinkolobwe mine in Katanga Province (Democratic Republic of Congo). Significant finds also come from Jáchymov in the Czech Republic, the Great Bear Lake mine in Canada, and numerous localities in Utah, USA (e.g., Delta mine).

Rarity

Not very common

For collectors

## Quality Criteria The most highly prized sklodowskite specimens are characterized by an intense, pure, lemon-yellow color. The crystal form is key – specimens with well-formed, long needles creating aesthetic, radial aggregates ("hedgehog" or "sunburst" formations) are sought after. Contrast with the dark host rock (matrix) and the absence of damage to the delicate crystals are also important. The size of the aggregates, rather than individual needles, significantly affects value. ## Popular Localities The Shinkolobwe deposit in the Democratic Republic of Congo is considered classic and provides the best specimens in the world. Specimens from there serve as a benchmark for this mineral. Collectors also value samples from Jáchymov (Czech Republic) due to their historical significance.

Care and storage

## Cleaning Sklodowskite specimens are extremely delicate and fragile. Mechanical cleaning is highly inadvisable. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Contact with water, which can damage the mineral, should be avoided. ## What to Avoid Sklodowskite is a uranium mineral and is strongly radioactive. Inhaling dust and direct skin contact must be strictly avoided. Washing hands after each contact is mandatory. It should not be stored in places where a lot of time is spent (bedrooms, desks). It should be protected from moisture, high temperatures, and chemicals. ## Storage It is recommended to store specimens in sealed, transparent plastic containers (so-called perky boxes), which protect against mechanical damage and dust dispersion. The container should be clearly labeled as radioactive material. It should be kept away from other radiation-sensitive minerals.

External references

Sources

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