Mourite

Chemical formula: U₆+O₂Mo₆+₅O₁₆·₅H₂O

A very rare uranyl molybdate, forming violet-blue, earthy aggregates in the oxidation zones of uranium-molybdenum deposits.

## Characteristics Mourite is a rare, secondary uranium and molybdenum mineral. It most often occurs as very fine-grained, earthy or compact aggregates and coatings. Its most characteristic feature is an intense, violet-blue or dark blue color, which can appear almost black in denser aggregates. Well-formed crystals are extremely rare and microscopic, taking the form of lamellae. ## Physical Properties This mineral is relatively soft, with a hardness of about 3 on the Mohs scale. Its density is approximately 4.2 g/cm³. The luster is described as vitreous to greasy on fresh surfaces. It is an opaque mineral, although very thin fragments may show slight translucency. ## Colors and Varieties The dominant and diagnostic color of mourite is a violet-blue hue. The intensity of the color depends on the degree of crystallinity and the density of the aggregate. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1962, refers to its chemical composition – the elements molybdenum (Mo) and uranium (Ur). It was discovered in one of the unspecified uranium-molybdenum deposits in Uzbekistan, which is its type locality. ## Applications Due to its extreme rarity, mourite has no industrial applications. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals and microminerals.

Properties

Mohs hardness: 3
Luster: Vitreous to greasy
Streak: Light blue
Density: 4.2
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque, translucent in thin splinters
Crystal system: Monoclinic

Diagnostic features

## Identification The key diagnostic feature is the unique violet-blue color combined with an earthy or fine-grained appearance. However, the most reliable identification method is measuring radioactivity with a Geiger counter, which is significantly elevated. The reaction to UV radiation is not characteristic. ## Distinguishing from Similar Minerals It can be confused with other blue or violet secondary minerals. - **Ilsemannite**: A similar, water-soluble molybdate with a blue color, but it is not radioactive. - **Covellite**: Has a similar color, but is a copper sulfide with a metallic luster and occurs in a completely different geological environment. - **Umohoite**: Often co-occurs with mourite, has a similar composition, but is usually black. ## Crystal Forms Most often forms earthy, powdery coatings or compact, fine-grained aggregates. Crystals, observed only under high magnification, take the form of microscopic lamellae or needles.

Geological environment

## Genesis Mourite is a secondary mineral, formed in the oxidation (weathering) zone of hydrothermal uranium-molybdenum deposits. It forms as a result of the alteration of primary uranium minerals (e.g., uraninite) and molybdenum minerals (e.g., molybdenite) under conditions of low temperatures and pressures. ## Mineral Associations It most often co-occurs with other secondary uranium and molybdenum minerals, such as umohoite, powellite, wulfenite, as well as jordisite and gypsum. ## Localities This is an extremely rare mineral. The main and practically only source of specimens is its type locality – an unspecified U-Mo deposit in Uzbekistan. Occurrences in other parts of the world have not been unequivocally confirmed or are insignificant from a collector's point of view.

Rarity

Very rare

For collectors

## Quality Criteria In the case of such a rare mineral, every specimen is valuable. Samples with distinct, rich aggregates of intense, violet-blue color, set on a small rock matrix, are most highly valued. Due to its microscopic nature, quality is assessed under magnification. ## Popular Localities The only known place from which specimens available on the collector's market originate is the historical type locality in Uzbekistan. Obtaining new material is practically impossible.

Care and storage

## Cleaning Specimens should only be cleaned dry, using a soft brush or compressed air to remove dust. Any contact with water and other liquids should be avoided, as the mineral may be damaged. ## What to Avoid The mineral is highly radioactive. Inhaling dust and direct skin contact must be absolutely avoided. It should not be heated or exposed to chemicals. Prolonged exposure to sunlight may not be advisable. ## Storage Mourite specimens must be stored in special, sealed, and permanently labeled containers (preferably with a radioactivity symbol). They should be kept away from areas of permanent human presence, in a well-ventilated room, separate from other minerals that could be damaged by radiation.

Sources

IMA Mineral List (CNMNC)