Murataite-(Y)

Chemical formula: (Y,Na)₆Zn₂+(Zn₂+,Fe₃+)₄(Ti₄+,Nb₅+,Na)₁₂O₂₉(O,F,OH)₁₀F₄

Murataite-(Y) is an extremely rare, black oxide mineral with a complex chemical composition, found in agpaitic pegmatites.

## Characteristics Murataite-(Y) is a very rare oxide mineral with an exceptionally complex chemical composition, containing yttrium, zinc, titanium, and niobium. It forms small, black, isometric crystals, typically not exceeding 1 mm in size. Its crystals are cubic or octahedral, often with modified faces. It occurs as single, well-formed crystals embedded in the rock matrix. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale and a high density of about 4.69 g/cm³. It has a black streak and is opaque. The luster is described as metallic to submetallic. It does not exhibit cleavage, and its fracture is conchoidal. ## Colors and Varieties Murataite-(Y) is uniform in color – it occurs exclusively in black. No colored varieties or commercial forms are known. ## History and Name The mineral's name comes from Kiyoshi Murata (1909-1991), an American chemist who worked at the United States Geological Survey (USGS) and made significant contributions to the study of rare earth element geochemistry. The suffix -(Y) in the name indicates the dominance of yttrium in its chemical composition. The mineral was described and approved by the IMA in 1997. ## Applications Due to its extreme rarity and microscopic crystal sizes, murataite-(Y) has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals.

Properties

Mohs hardness: 5
Luster: Metallic to submetallic
Streak: Black
Density: 4.69
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Murataite-(Y) is recognizable by its black, isometric crystals with a metallic luster, occurring in a very specific geological environment – agpaitic pegmatites. Its high density and hardness of around 5 are helpful in identification. However, definitive confirmation requires advanced analytical methods, such as X-ray spectroscopy (EDS/WDS), due to its similarity to other rare oxides. ## Distinguishing from Similar Minerals It can be confused with other black, opaque minerals found in similar parageneses, such as pyrochlore, microlite, or uraninite. Distinguishing it from these minerals "by eye" is practically impossible and requires specialized chemical analysis to determine the dominant elements. ## Crystal Forms Murataite-(Y) crystals are isometric and take the form of cubes, octahedra, and their combinations. They are usually well-formed but are microscopic in size, rarely exceeding 1 mm.

Geological environment

## Genesis Murataite-(Y) forms in the late stages of crystallization of agpaitic pegmatites, which are extremely saturated with alkaline elements and rare earth elements. It crystallizes under conditions of low silica activity. ## Mineral Associations This mineral co-occurs with other rare minerals typical of pegmatites from the Lovozero Massif, such as eudialyte, lorenzenite, nepheline, sodalite, ussingite, vuonnemite, zorite, lomonosovite, and steenstrupine-(Ce). ## Localities The only confirmed occurrence of murataite-(Y) in the world is its type locality – Mount Alluaiv in the Lovozero Massif on the Kola Peninsula, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The most important criterion for evaluating a murataite-(Y) specimen is the quality and size of the crystals. Specimens with sharp, well-formed crystals that stand out clearly from the rock matrix are sought after. Due to the microscopic nature of the mineral, even crystals 1 mm in size are considered exceptional. Contrast with a light-colored associated mineral (e.g., ussingite) significantly enhances the visual appeal of the specimen. ## Popular Localities The only source of murataite-(Y) specimens is the Lovozero Massif on the Kola Peninsula, Russia. Specimens from this locality, especially from Mount Alluaiv, are the only ones available on the collector's market.

Care and storage

## Cleaning Specimens of murataite-(Y) should be cleaned very carefully, preferably using compressed air to remove dust. Due to the microscopic size of the crystals, mechanical cleaning (e.g., with a brush) and contact with water, which could react with associated minerals, are discouraged. ## What to Avoid Avoid contact with all chemicals, including acids and bases. Specimens should not be subjected to ultrasonic cleaning. The mineral is stable, but it should be protected from extreme changes in temperature and humidity. ## Storage Specimens should be stored in stable conditions, in closed collector boxes or display cases, to protect them from dust and mechanical damage. Due to the small size of the crystals, storage in "micromount" type boxes is recommended.

Sources

IMA Mineral List (CNMNC)