Yttrotantalite-(Y)

Chemical formula: (Y,U₆+,Fe₂+)(Ta₅+,Nb₅+)₂(O,OH)₄

A rare mineral from the oxide group, containing yttrium and tantalum, characterized by its black color, high density, and radioactivity.

## Characteristics Yttrotantalite-(Y) is a complex oxide of tantalum, niobium, yttrium, and uranium. It occurs as irregular masses or rare, poorly formed crystals. Its surface is usually dull or coated with a film, but a fresh fracture reveals a luster ranging from submetallic to resinous to greasy. It is typically opaque, black, brownish-black, or brown. Due to its uranium and thorium content, this mineral undergoes metamictization, a gradual destruction of its crystal lattice by ionizing radiation. This leads to the loss of its original structure and transition to an amorphous state, which affects its physical properties. ## Physical Properties The Mohs hardness of yttrotantalite-(Y) is 5 to 5.5. It is a brittle mineral with a conchoidal to uneven fracture. Its density is significant, ranging from 5.5 to 5.9 g/cm³, which is noticeable when holding a specimen. The luster on fresh surfaces is submetallic, resinous, or greasy. It is an opaque mineral. ## Colors and Varieties The dominant color is black, often with a brown or gray tint. No distinct color varieties or commercial varieties are recognized. Chemical variability primarily concerns the tantalum to niobium ratio and the content of other rare earth elements. ## History and Name The mineral's name, given in 1802, directly refers to its chemical composition – the presence of yttrium and tantalum. The suffix -(Y) was added later, in accordance with the rules for naming minerals with rare earth elements, to indicate that yttrium is the dominant element in that structural position. The type locality where this mineral was first described is the famous pegmatite quarry in Ytterby, Sweden. ## Applications Yttrotantalite-(Y) has no industrial significance as a source of yttrium or tantalum due to its rarity. However, it is an object of scientific interest and a valued collector's mineral, sought after for its rarity, chemical composition, and origin from classic pegmatite localities.

Properties

Mohs hardness: 5 - 5.5
Luster: Sub-metallic, resinous, greasy
Streak: Grey, brownish to black
Density: 5.5 - 5.9
Cleavage: Indistinct on {010}
Fracture: Sub-conchoidal to uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Key diagnostic features of yttrotantalite-(Y) are: high density, black or brownish-black color, resinous or submetallic luster on a fresh fracture, and occurrence in granitic pegmatites. The most important feature, however, is its radioactivity, which can be easily detected with a Geiger-Müller counter. The reaction to radiation is often the decisive test. ## Distinguishing from Similar Minerals Yttrotantalite-(Y) can be confused with other black, heavy pegmatite minerals, such as: - **Samarskite**: Often has a stronger vitreous to resinous luster and a very distinct conchoidal fracture. It is also radioactive. Differentiation without chemical analysis is very difficult. - **Columbite-(Fe) and Tantalite-(Fe)**: Usually have a more metallic luster and often form better-developed, tabular or prismatic crystals. Their radioactivity is significantly lower or absent. - **Euxenite-(Y)**: Has a very similar appearance and physical properties, and is also radioactive. Certain differentiation requires advanced analytical methods (e.g., XRD, EDS). ## Crystal Forms Yttrotantalite-(Y) crystals are rare and usually poorly formed, with a short-prismatic or tabular habit. It is most commonly found as irregular, embedded grains and aggregates within the rock mass.

Geological environment

## Genesis Yttrotantalite-(Y) is a primary mineral, crystallizing from residual magma in the late stages of the formation of granitic pegmatites, especially those rich in rare earth elements, niobium, and tantalum (NYF-type pegmatites - Niobium-Yttrium-Fluorine). ## Mineral Associations This mineral co-occurs with other minerals typical of rare earth pegmatites. Its most common associations include: albite, quartz, microcline, muscovite, biotite, gadolinite-(Y), fergusonite-(Y), samarskite-(Y), monazite-(Ce), zircon, tantalite-(Mn), and euxenite-(Y). ## Localities Important and historical localities for yttrotantalite-(Y) include: - **Sweden**: Ytterby on Resarö island (type locality). - **Norway**: Numerous pegmatites in the Iveland, Evje og Hornnes, and Kragerø regions. - **USA**: Baringer Hill district in Texas and pegmatites in Colorado. - **Russia**: Ilmen Mountains in the Southern Urals. - **Madagascar**: Betafo region.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, even if partially, crystals are most highly valued by collectors. Due to the rarity of such forms, even crystal fragments are desirable. The locality is also of great importance – specimens from the type locality (Ytterby) have particular historical value. The attractiveness is enhanced by the presence of yttrotantalite-(Y) on a rock matrix, accompanied by other rare pegmatite minerals. ## Popular Localities Although Ytterby in Sweden is historically the most important, most collector specimens currently come from rare-earth-rich pegmatites in southern Norway (e.g., from the Iveland area). Specimens from these localities are valued for their relatively good formation and size.

Care and storage

## Cleaning Yttrotantalite-(Y) specimens should only be cleaned mechanically, using a soft brush or paintbrush. Distilled water can be used to remove loose contaminants. Ultrasonic cleaners should be avoided, as they can damage brittle, metamict specimens. ## What to Avoid The mineral is radioactive due to its uranium content. Direct contact should be minimized, and hands should be washed after each contact. It should not be stored in areas of permanent human presence (bedrooms, desks). Cutting, grinding, and other dust-generating activities should be avoided to prevent inhalation of radioactive dust. It should not be stored in direct contact with radiation-sensitive minerals (e.g., topaz, some quartzes), as it may cause changes in their color. ## Storage It is recommended to store specimens in separate, tightly sealed containers (e.g., plastic), away from the main part of the collection. The room should be well-ventilated. Each specimen should be clearly labeled with information about its radioactivity.

Sources

IMA Mineral List (CNMNC)