Monazite-(Gd)

Chemical formula: Gd(PO₄)

Monazite-(Gd) is an extremely rare, radioactive mineral from the monazite group, distinguished by the dominance of gadolinium in its chemical composition.

## Characteristics Monazite-(Gd) is a mineral belonging to the monazite group, where individual "species" are defined by the dominant rare-earth element. In this case, it is gadolinium (Gd). This mineral forms very small, sub-millimeter crystals with a tabular or prismatic habit, often with rounded edges. It usually occurs as inclusions in other minerals. Its identification is possible almost exclusively by advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Physical Properties Due to its extreme rarity and microscopic crystal sizes, most physical properties have not been fully studied and are extrapolated from data for other minerals in the monazite group. Hardness is estimated at approximately 5 on the Mohs scale. The mineral exhibits strong radioactivity due to the possible presence of thorium and uranium, which substitute for rare-earth elements in the structure. ## Colors and Varieties Observed crystals range in color from pale yellow to yellowish-brown. No varieties of this mineral are distinguished. ## History and Name The name "monazite-(Gd)" reflects its belonging to the monazite group and the dominance of gadolinium (Gd) in its composition, in accordance with IMA mineral nomenclature rules. It was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2022. The discovery was made on material originating from the Uleberg granite quarry, in the municipality of Iveland, Norway. ## Applications Monazite-(Gd) has no commercial or industrial applications. Its significance is purely scientific and collectible, as evidence of the geochemical differentiation of rare-earth elements in the Earth's crust.

Properties

Mohs hardness
5
Luster
Resinous
Streak
White
Density
5.55
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of monazite-(Gd) under amateur conditions is impossible. It requires specialized laboratory equipment, such as a scanning electron microscope with an EDS or WDS attachment, to confirm the dominance of gadolinium over other rare-earth elements. Visually, it is indistinguishable from other minerals in the monazite group. ## Distinguishing from Similar Minerals It can be confused with other minerals from the monazite group (monazite-(Ce), monazite-(La), monazite-(Nd)), xenotime, zircon, or thorite. Differences can only be determined based on chemical composition analysis. ## Crystal Forms It forms very small, tabular or short-prismatic crystals, often grouped into small aggregates. Crystals rarely exceed a few tens of micrometers in size.

Geological environment

## Genesis Monazite-(Gd) forms in the late stages of crystallization of granites and granitic pegmatites, rich in rare-earth elements. It crystallizes in a hydrothermal environment, in the presence of phosphorus. ## Mineral Associations It co-occurs with minerals typical of granitic pegmatites, such as albite, microcline, quartz, biotite, as well as with other rare-earth minerals, e.g., xenotime-(Y), fergusonite-(Y), and other minerals from the monazite group. ## Localities The only confirmed occurrence (type locality) is the Uleberg granite quarry in Iveland, Agder region, Norway. This is the only place in the world where this mineral has been identified.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its microscopic nature, the main criterion for a specimen's value is the quality of the analysis confirming its identity and the richness of the mineral association on the host rock. The size of the crystals, even if sub-millimeter, is important. The most desirable specimens are those with clearly visible (under a microscope) well-formed crystals, embedded on an aesthetic rock matrix. ## Popular Localities The only source of specimens is the type locality – the Uleberg quarry in Norway. Specimens from this location are highly valued by collectors specializing in mineral systematics and rare-earth minerals.

Care and storage

## Cleaning Specimens of monazite-(Gd) are typically microscopic and embedded in the host rock. They do not require and should not be subjected to mechanical or chemical cleaning, so as not to damage the delicate crystals or surrounding minerals. ## What to Avoid Avoid contact with acids and strong chemicals. As a radioactive mineral, it requires careful handling. Although individual, microscopic specimens do not pose a significant threat, avoid inhaling dust and wash hands after contact. It should not be stored in bedrooms or areas of permanent human presence. ## Storage Specimens should be stored in specialized, tightly sealed containers (so-called perky boxes), away from other radiation-sensitive minerals (e.g., smoky quartz, some fluorites). The container should be clearly labeled as containing a radioactive mineral.

External references

Sources

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