Tveitite-(Y)

Chemical formula: (Y,Na)₆(Ca,Na,Y,REE)₁₂(Ca,Na)F₄₂

Tveitite-(Y) is a rare yttrium and calcium fluoride, forming small, colorless or white platy crystals, valued by collectors of rare minerals.

## Characteristics Tveitite-(Y) is a complex fluoride belonging to the tveitite group. It occurs as very small, hexagonal, platy or thin-tabular crystals, rarely exceeding 1 mm. It typically forms aggregates or rosettes. It is a colorless, white, or pale yellow mineral, often with a pearly luster on cleavage surfaces. ## Physical Properties The mineral has a hardness of approximately 4 on the Mohs scale. It exhibits perfect cleavage in one direction, causing it to easily split into thin lamellae. Its luster is vitreous, and pearly on cleavage planes. It is transparent to translucent. ## Colors and Varieties Typical colors are white, colorless, and sometimes pale yellow. No named varieties of this mineral are distinguished. ## History and Name The mineral is named after John Tveit, a Norwegian mineral collector who found the first specimens. It was described in 1977 by Gunnar Raade, Matias H. Mledecka, Henrich Neumann, B. B. Jensen, and A. K. Nilsen. The suffix "-(Y)" indicates the dominance of yttrium in its chemical composition. ## Applications Due to its rarity and small crystal size, Tveitite-(Y) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and a subject of scientific research.

Properties

Mohs hardness
4
Color
White to pale yellow
Luster
Vitreous, Pearly
Streak
White
Density
3.94
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Characteristic features include the hexagonal outline of crystals, platy habit, perfect cleavage in one direction, and pearly luster on cleavage planes. Occurrence in a specific geological environment (granitic pegmatites) in association with other rare minerals is also an important clue. ## Distinguishing from Similar Minerals It can be confused with other platy minerals, such as micas (e.g., Muscovite) or Gagarinite-(Y). It differs from micas by its higher density and lack of elasticity of the lamellae. It is difficult to distinguish from Gagarinite-(Y) without advanced chemical analyses (EDS/WDS), although Gagarinite-(Y) often forms more prismatic crystals. ## Crystal Forms It forms thin, tabular or platy crystals with a hexagonal outline. They often occur as fan-shaped or rosette-like aggregates.

Geological environment

## Genesis It is a hydrothermal mineral, occurring in granitic pegmatites, especially in their late, altered zones. It forms under low-temperature conditions in the presence of rare earth elements and fluorine. ## Mineral Associations It often co-occurs with other rare minerals, such as Fluorite, Yttrofluorite, Gagarinite-(Y), Stenonite-(Y), Cryolite, Jarlite, as well as Quartz, Microcline, and Albite. ## Localities The most important and classic locality (type locality) is the Høydalen quarry in Tørdal, Telemark region, Norway. Other known localities include alkaline complexes on the Kola Peninsula in Russia and pegmatites in the Pikes Peak area in Colorado, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp crystals with a distinct hexagonal outline, forming aesthetic aggregates. Crystal size is also important – specimens exceeding a millimeter are rare. Contrasting placement on a rock matrix, for example on Quartz or Fluorite, significantly enhances visual and collector value. ## Popular Localities Undoubtedly, the most sought-after and classic specimens come from the original locality in Høydalen, Norway. Specimens from other places, such as the Kola Peninsula, are also valued, but Norwegian ones serve as the standard for this mineral.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its perfect cleavage, mechanical and ultrasonic cleaning should be avoided. If liquid is necessary, pure distilled water or isopropyl alcohol is recommended, applied with great gentleness. ## What to Avoid Avoid contact with acids and other aggressive chemicals. The mineral is brittle and easily damaged mechanically, so it should be protected from impacts and scratches. It should not be subjected to sudden temperature changes. ## Storage Tveitite-(Y) specimens are typically small and delicate, so it is best to store them in closed "micromount" boxes, lined with soft material, to protect them from dust and mechanical damage.

External references

Sources

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