Tengerite-(Y)

Chemical formula: Y<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>·2-3H<sub>2</sub>O

A hydrous yttrium carbonate, most commonly found as white, chalky, or powdery coatings on other minerals.

## Characteristics Tengerite-(Y) is a secondary mineral from the carbonate group, containing yttrium and water. It forms characteristic white or grayish-white coatings and crusts that resemble chalk or dried paint. It occurs as earthy, powdery aggregates, as well as radial or spherulitic aggregates with a fibrous structure. Due to its appearance and small aggregate size, it is easily overlooked. Well-formed crystals are extremely rare and microscopic in size. ## Physical Properties It is a very soft mineral, with a hardness ranging from 2-3 on the Mohs scale, meaning it can be scratched with a fingernail. Its luster is most often dull or earthy, although fibrous aggregates may exhibit a silky luster. It is translucent in thin fragments and opaque in mass. The calculated density is approximately 3.12 g/cm³. ## Colors and Varieties This mineral is typically pure white. It may take on grayish or yellowish hues, which is a result of the presence of impurities or inclusions of other minerals. No distinct color varieties or commercial varieties are recognized. ## History and Name The name tengerite-(Y) comes from the Swedish chemist Lars Gustaf von Tenger. The mineral was first described in 1838 by Carl Gustaf Mosander. The type locality is the quarry in Ytterby, Sweden, a site where many rare earth elements, including yttrium, were discovered. ## Uses Tengerite-(Y) has no industrial application. It is solely an object of interest for collectors of rare minerals and scientists studying the weathering processes of rocks rich in rare earth elements.

Properties

Mohs hardness
2-3
Luster
Dull, earthy, silky
Streak
White
Density
3.12
Cleavage
Perfect on {100}, good on {010}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification A characteristic feature of tengerite-(Y) is its occurrence as white, chalk-like coatings on rare earth element minerals (such as gadolinite) in pegmatites. Its low hardness and violent reaction with hydrochloric acid (with CO₂ evolution) are key diagnostic indicators. Under ultraviolet light, it may exhibit weak, whitish or creamy fluorescence. ## Distinguishing from Similar Minerals It can be confused with other secondary REE carbonates, such as kimuraite-(Y) or lokkaite-(Y). Reliable differentiation from these is almost exclusively possible using advanced analytical methods (e.g., XRD, EDS). It is distinguished from common calcite or aragonite by its geological context – its occurrence in paragenesis with REE minerals. ## Crystal Forms Most commonly found as earthy, powdery, and chalky coatings and crusts. Less frequently, it forms radial aggregates of fine fibers or small spherulites. Macroscopic, well-formed crystals are practically non-existent.

Geological environment

## Genesis Tengerite-(Y) is a secondary mineral. It forms in the weathering zone of granitic pegmatites as a result of the alteration of primary minerals rich in yttrium and other rare earth elements, such as gadolinite-(Y), euxenite-(Y), or fergusonite-(Y). It is a product of their decomposition under the influence of carbon dioxide-containing waters. ## Mineral Associations It most often co-occurs with the minerals from which it forms, i.e., gadolinite-(Y), fergusonite-(Y), euxenite-(Y), and allanite. It is also accompanied by the main rock-forming minerals of pegmatites, such as quartz, microcline, albite, and biotite. It can occur together with other secondary REE minerals. ## Localities Key global localities include classic sites in Scandinavia: Ytterby in Sweden (type locality) and the Iveland area in Norway. It is also known from pegmatites in Baveno, Italy, the Pikes Peak region in Colorado (USA), Mount Suishoyama in Japan, and Mont Saint-Hilaire in Canada.

Rarity

Not very common

For collectors

## Quality Criteria The collector's value of tengerite-(Y) is inextricably linked to the specimen on which it occurs. The most prized are rich, pure white coatings covering well-formed crystals of rare primary minerals, e.g., black, lustrous gadolinite-(Y) crystals. The coating itself, without an interesting substrate, has significantly less value. Provenance from a classic, well-known locality is also important. ## Popular Localities Specimens from historical localities, such as Ytterby in Sweden or Iveland in Norway, are particularly sought after by advanced collectors of rare minerals. Visually attractive combinations of tengerite with other minerals also come from pegmatites in Colorado, USA.

Care and storage

## Cleaning Tengerite-(Y) is extremely delicate, soft, and often brittle. Mechanical cleaning with brushes is strongly discouraged, as it can permanently remove the coating from the specimen. The safest method is gentle blowing with compressed air from a safe distance to remove dust. ## What to Avoid Avoid contact with water, and especially with acids, with which it reacts violently (effervesces). As a hydrated mineral, it can be sensitive to high temperatures, which can lead to its dehydration and destruction. It should be protected from all chemicals and ultrasound. ## Storage Specimens with tengerite-(Y) require special protection against mechanical damage. It is best to store them in closed “micromount” boxes, which protect delicate coatings from abrasion and contact with other minerals. Avoid places with high humidity or exposed to direct sunlight.

Sources

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