Nuragheite

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

Nuragheite is an extremely rare, secondary thorium molybdate mineral, forming microscopic, tabular crystals of white color with a pearly luster.

## Characteristics Nuragheite is a hydrated thorium molybdate, occurring as extremely small, thin, tabular crystals that rarely exceed 200 micrometers. These crystals form rosette-like or spherical aggregates. Due to their microscopic size, visual features are difficult to observe without specialized equipment. ## Physical Properties Nuragheite crystals are flexible and pliable. Hardness and density have not been precisely measured due to the small size of samples and their fragility. The density calculated based on the chemical formula and unit cell parameters is 5.13 g/cm³. The mineral is characterized by a pearly luster on cleavage surfaces and a vitreous luster on other faces. ## Colors and Varieties Nuragheite is colorless to white. No varieties have been distinguished. ## History and Name The mineral was discovered in the Su Seinargiu mine in Sardinia, Italy. Its name, approved by the International Mineralogical Association (IMA) in 2011, comes from the nuraghes – megalithic structures from the Bronze Age, characteristic of Sardinia. It refers to the mineral's discovery location. ## Uses Nuragheite has no industrial application. It is of scientific and collector's interest only due to its extreme rarity and chemical composition.

Properties

Luster
Pearlaceous
Streak
White
Density
5.13
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of nuragheite is possible only through advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), combined with chemical analysis (EDS). Visual identification in the field or in a collection is impossible due to the microscopic size of the crystals and their similarity to other secondary molybdenum minerals. ## Distinguishing from Similar Minerals Nuragheite can be confused with other secondary molybdates, such as schenite, iriginite, or umohoite, with which it often co-occurs. Differentiation requires specialized laboratory tests. Nuragheite is distinguished by its unique combination of thorium and molybdenum in its chemical composition. ## Crystal Forms It forms very thin, tabular crystals with a hexagonal or rhombic outline, flattened parallel to the {010} plane. These crystals often combine into rosette-like, spherical, or radial aggregates.

Geological environment

## Genesis Nuragheite is a secondary mineral, forming in the oxidation (weathering) zone of molybdenum-lead deposits. It forms as a result of hydrothermal processes occurring in altered granitic rocks, in the presence of thorium and molybdenum-rich solutions. ## Mineral Associations It co-occurs with other secondary molybdenum and uranium minerals, such as iriginite, umohoite, schenite, mushingite, wulfenite, as well as quartz, fluorite, and galena. ## Localities The only confirmed occurrence of nuragheite in the world is its type locality – the Su Seinargiu mine near Sarroch, in the province of Cagliari, Sardinia, Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the mineral, the main criterion for evaluation is the quality and richness of aggregates on the rock matrix. Specimens with clearly formed, rosette-like crystal clusters, well visible under a microscope, are most valued. Association with other rare secondary minerals is also important. ## Popular Localities All known collector specimens come from a single location in the world: the Su Seinargiu mine in Sardinia, Italy. This makes every specimen, regardless of its quality, an extremely valuable acquisition for specialized collectors of rare minerals and "micromounts."

Care and storage

## Cleaning Nuragheite specimens should not be cleaned mechanically or chemically. Any attempts at cleaning may irreversibly damage the delicate, microscopic crystals. If dust removal is necessary, it can be done very carefully with a photographic air blower, from a safe distance. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any vibrations or shocks. The mineral is extremely fragile and sensitive to environmental changes. Due to its thorium content, it is a radioactive mineral and should be handled with appropriate precautions. ## Storage Store only in stable, sealed "micromount" containers, protecting against dust, moisture, and mechanical damage. It should be kept away from other minerals that could be damaged by radiation.

External references

Sources

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