Sengierite

Chemical formula: Cu<sup>2+</sup><sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>·6H<sub>2</sub>O

Sengierite is a rare, bright green uranium and vanadium mineral, forming tabular crystals and characteristic radial aggregates.

## Characteristics Sengierite is a hydrated uranyl vanadium and copper mineral. It forms very small, thin, tabular crystals, often with a hexagonal outline, which rarely exceed 1 mm. It typically occurs as rosetted or radial aggregates, as well as scaly masses and coatings. Its intense, bright color is very characteristic. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of approximately 2.5. It has a vitreous luster, and on cleavage surfaces, it can be pearly. It is a heavy mineral due to the presence of uranium, with a density of 4.1 g/cm³. It exhibits strong radioactivity. ## Colors and Varieties Sengierite occurs in shades from yellowish-green to olive-green. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1949 by Johannes Vaes and Paul Kerr, honors Edgar Sengier (1879-1963), director of the Belgian mining company Union Minière du Haut Katanga, which managed the Shinkolobwe mine. He played a key role in supplying uranium for the American Manhattan Project. ## Uses Due to its rarity and small crystal size, sengierite has no industrial application. It is of purely scientific and collectible interest.

Properties

Mohs hardness
2.5
Luster
Vitreous, Pearly
Streak
Pale green
Density
4.1
Cleavage
Perfect on {001}
Fracture
Micaceous
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Sengierite can be identified by its characteristic bright, yellowish-green color, tabular crystal habit, and tendency to form radial aggregates and rosettes. Its strong radioactivity is a key diagnostic feature. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals, such as torbernite or zeunerite, which also have a green color and tabular habit. Sengierite differs from them by subtle differences in hue (it is more yellowish-green) and its co-occurrence with vanadium minerals. Final distinction often requires chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms Crystals are thin-tabular, flattened parallel to {001}, with a pseudohexagonal outline. They most often form fan-shaped, rosetted, and radial aggregates, as well as fine-scaly coatings and crusts.

Geological environment

## Genesis Sengierite is a secondary mineral formed in the oxidation zones (weathering) of uranium-vanadium deposits. It forms as a result of the alteration of primary uranium minerals (such as uraninite) and vanadium in the presence of copper-rich solutions. ## Mineral Associations It most commonly co-occurs with other secondary uranium and vanadium minerals. Typical associated minerals include carnotite, tyuyamunite, metatorbernite, volborthite, as well as malachite, chalcocite, and uraninite. ## Localities The most important and classic occurrence (type locality) is the Shinkolobwe mine in Haut-Katanga Province, Democratic Republic of Congo. It is also known from several other localities worldwide, including the Monument No. 2 mine in Apache County, Arizona (USA), and the Ore Mountains region in Saxony (Germany).

Rarity

Rare

For collectors

## Quality Criteria The most prized sengierite specimens are characterized by well-formed, sharp crystals forming aesthetic, radial aggregates or rosettes. The intensity and saturation of the yellowish-green color also increase the specimen's value. Contrast with the rock matrix and the presence of rare associated minerals are important. Due to the small size of the crystals, specimens with visible, larger (even 1-2 mm) crystals are particularly sought after. ## Popular Localities Undoubtedly, the most desirable and classic specimens come from the type locality – the Shinkolobwe mine in the Democratic Republic of Congo. They serve as the benchmark for this mineral.

Care and storage

## Cleaning Sengierite specimens should not be wet cleaned. A soft brush or compressed air from a safe distance can be used to remove dust. Avoid contact with water, which can damage the delicate crystals. ## What to Avoid Absolutely avoid contact with water, acids, and other chemicals. The mineral is sensitive to heat. As a uranium mineral, it is strongly radioactive – limit exposure, wash hands after each contact, and never inhale dust. ## Storage Sengierite must be stored in specialized, sealed, and appropriately labeled containers designed for radioactive minerals. It should be kept away from other radiation-sensitive minerals and away from areas of permanent human habitation.

External references

Sources

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