Cousinite

Chemical formula: MgU<sup>4+</sup><sub>2</sub>(Mo<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·2H<sub>2</sub>O (?)

Cousinite is a discredited mineral (considered a mixture), originally described as a rare uranium and magnesium molybdate from Congo.

## Characteristics Cousinite is the name given to a material that is currently recognized as a discredited mineral by the International Mineralogical Association (IMA). It was originally described as a distinct mineral species, but subsequent studies have shown that it is most likely a mixture of other minerals, such as uraninite and molybdenite, or a product of umohoite alteration. In its original description, it was characterized as black, silky coatings and aggregates of fine, acicular crystals. ## Physical Properties This mineral forms opaque, black aggregates with a silky luster. Due to its status as a discredited mixture, no reliable and repeatable physical data, such as hardness or density, have been determined for it. ## Colors and Varieties Described exclusively as black. No color varieties are known. ## History and Name The name cousinite was given in honor of Maurice Coussens, a geologist working for Union Minière du Haut Katanga. The mineral was first described by J.F. Vaes in 1947 based on samples from the Shinkolobwe mine in the Democratic Republic of Congo. In 1988, it was officially discredited by the IMA after analyses failed to confirm its status as a homogeneous mineral phase. ## Applications Cousinite has no industrial application. Its significance is purely historical and scientific, and specimens may be of interest to specialized collectors of uranium minerals and rare, historical materials.

Properties

Luster
Silky
Streak
Black
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification is primarily based on historical context and location. It is recognized by its black color, fibrous or acicular aggregate form, and silky luster. A key feature is its strong radioactivity. Definitive confirmation that one is dealing with the material described as cousinite would require advanced analyses (e.g., XRD, SEM-EDS) to show that it is a mixture. ## Distinguishing from Similar Minerals It can be confused with other black, secondary uranium minerals with a fibrous appearance, such as umohoite. Visually, it may also resemble sooty aggregates of uraninite or molybdenite. Differentiation without specialized analytical equipment is practically impossible. ## Crystal Forms It has been described as forming very fine, acicular crystals gathered in fibrous, felted, or radial aggregates and coatings.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zone of hydrothermal uranium deposits. Its only known location is an environment rich in uranium and molybdenum. ## Mineral Associations It occurs in association with other uranium minerals, such as uraninite, rutherfordine, schoepite, becquerelite, masuyite, kasolite, curite, and soddyite. ## Localities The only confirmed occurrence of the material described as cousinite is the historical Shinkolobwe uranium mine in Katanga Province, Democratic Republic of Congo. This mine is currently closed and flooded.

Rarity

Extremely rare

For collectors

## Quality Criteria In the case of a discredited mineral, the value of a specimen lies in its historical significance and provenance. The most desirable samples are those with original, old labels from the period when cousinite was still considered a valid mineral species. Visual quality, i.e., the richness and extent of the black, fibrous coatings, is of secondary importance. ## Popular Localities The only source of specimens is the Shinkolobwe mine in the DRC. As it has long been inactive, material from this locality is only available on the secondary market and has high historical value.

Care and storage

## Cleaning As a radioactive and potentially brittle material, it should not be wet cleaned. For dust removal, a soft brush or compressed air from a safe distance can be used. Inhaling dust should be avoided. ## What to Avoid Contact with water and chemicals should be strictly avoided. As a uranium mineral, it is radioactive and requires careful handling. Hands should be washed after each contact, and it should not be stored in areas of permanent human presence. ## Storage Cousinite specimens must be stored in sealed, lead-lined or glass containers, clearly marked as radioactive material. They should be kept away from other radiation-sensitive minerals and in a well-ventilated room, away from bedrooms and living areas.

Sources

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