Clinofergusonite-(Y)

Chemical formula: YNb⁵⁺O₄

Clinofergusonite-(Y) is a rare, naturally occurring yttrium niobate, a polymorph of fergusonite-(Y) with a monoclinic crystal structure.

## Characteristics Clinofergusonite-(Y) is a mineral belonging to the fergusonite group, characterized by a monoclinic crystal structure. It typically forms very small, poorly developed crystals, usually less than 1 mm in size, often with prismatic or dipyramidal habit. It occurs as grains or aggregates. This mineral is usually opaque, ranging in color from yellowish-brown to dark brown, and its luster is described as vitreous to resinous. ## Physical Properties Due to its rarity and small crystal size, many physical properties have not been fully investigated. Its Mohs hardness is estimated to be 5.5 to 6.5, similar to other minerals in its group. The density calculated based on its chemical formula and unit cell parameters is 5.69 g/cm³. The mineral exhibits weak cleavage. ## Colors and Varieties Clinofergusonite-(Y) occurs in shades of brown – from yellowish-brown, through reddish-brown, to dark brown. No named varieties are distinguished. ## History and Name The mineral's name refers to its monoclinic crystal structure and its chemical composition, which is dominated by yttrium (Y). It is a polymorph (a variety with the same chemistry but a different structure) of tetragonal fergusonite-(Y). It was formally described as a distinct mineral relatively recently, after the discovery of its unique structure. ## Applications Clinofergusonite-(Y) has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare representative of rare-earth niobates.

Properties

Mohs hardness
5.5-6.5
Color
Pale yellow
Luster
Vitreous to Resinous
Streak
Brown
Density
5.65
Cleavage
Poor on {010}
Fracture
Sub-Conchoidal
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of clinofergusonite-(Y) is extremely difficult without advanced analytical methods. Due to its occurrence as very small grains, visual recognition is practically impossible. Key features include its brown color, resinous luster, and high density. Definitive confirmation requires chemical analysis (EDS) to confirm the presence of yttrium and niobium, and X-ray diffraction (XRD) to determine its monoclinic crystal structure. ## Distinguishing from Similar Minerals It can be confused with other minerals from the fergusonite group, such as fergusonite-(Y) (tetragonal) and fergusonite-(Ce). Differentiation from tetragonal fergusonite-(Y) is only possible using diffraction methods. Other similar brown, heavy minerals (e.g., zircon, monazite, euxenite) require chemical analysis for distinction. ## Crystal Forms It forms small, prismatic or dipyramidal crystals, often with poorly developed faces. It is most commonly found as irregular grains embedded in the host rock.

Geological environment

## Genesis Clinofergusonite-(Y) is an accessory mineral in granites and granitic pegmatites, especially those enriched in rare-earth elements. It forms in the late stages of magma crystallization in an yttrium- and niobium-rich environment. ## Mineral Associations It often co-occurs with other minerals typical of pegmatites, such as albite, microcline, quartz, biotite, as well as other rare-earth minerals, e.g., euxenite-(Y), allanite, monazite, xenotime, and zircon. ## Localities The most important confirmed occurrences of this rare mineral are in Norway (Iveland, Evje og Hornnes), Sweden (Ytterby), Japan (various localities on Honshu island), and Italy (Baveno, Piedmont).

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of clinofergusonite-(Y) primarily depends on the degree of crystal development and their size. Specimens with distinct, sharp crystal faces, even if small, are much more valued than irregular grains. Well-documented locality and confirmed mineral identification using analytical methods are also important. Contrast with a light host rock (e.g., white albite) enhances aesthetic value. ## Popular Localities Specimens from classic localities in Norway and Sweden are historically significant, however, the best crystallographically developed microcrystals come from granitic miaroles in Baveno, Italy.

Care and storage

## Cleaning Due to the small size and fragility of specimens, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemical agents. ## What to Avoid Avoid ultrasonic cleaners, steam cleaners, acids, and all chemical solvents. The mineral may be sensitive to rapid temperature changes. As a metamict (or partially metamict) mineral, its structure can be sensitive to heating. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" boxes, to protect them from dust and mechanical damage. Avoid exposure to moisture and direct sunlight.

External references

Sources

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