Allanite-(Nd)

Chemical formula: CaNdAl<sub>2</sub>Fe<sup>2+</sup>(Si<sub>2</sub>O<sub>7</sub>)(SiO<sub>4</sub>)O(OH)

Allanite-(Nd) is a very rare mineral from the epidote group, distinguished by the dominance of neodymium in its chemical composition.

## Characteristics Allanite-(Nd) is a mineral belonging to the allanite subgroup within the epidote group. Its name indicates the dominance of the rare earth element – neodymium (Nd) – in its structure. It forms irregular, anhedral grains up to several millimeters in size, often intergrown into small aggregates. Well-formed crystals are not known. It is usually black to brownish-black and opaque. ## Physical Properties The mineral is characterized by a submetallic, greasy, or resinous luster. Its hardness has not been precisely determined. The density calculated based on chemical composition and unit cell parameters is 4.15 g/cm³. It is brittle, and its fracture is uneven to subconchoidal. ## Colors and Varieties Allanite-(Nd) occurs in uniform colors: black or brownish-black. It does not form color varieties, and in itself, it is a specific variety of allanite, defined by the predominance of neodymium over other rare earth elements. ## History and Name The mineral's name refers to its belonging to the allanite subgroup and to the dominant neodymium (Nd) in its composition. It was officially recognized by the International Mineralogical Association (IMA) in 2003. It was described by Japanese researchers based on material collected from the Komatsu quarry in Japan, which is its type locality. ## Applications Allanite-(Nd) has no industrial application. Its significance is purely scientific and collectible, as a very rare mineral and a representative of the allanite group with a specific chemical composition.

Properties

Luster
Submetallic to resinous
Streak
Grayish brown
Density
4.15 (obliczona)
Cleavage
Imperfect on {001}
Fracture
Uneven to subconchoidal
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Visual identification is practically impossible. Allanite-(Nd) occurs as black, opaque, anhedral grains with a submetallic or resinous luster. A key diagnostic clue is its specific occurrence environment – in limestone xenoliths within serpentinites, in association with minerals such as vesuvianite, garnet, and diopside. ## Distinguishing from Similar Minerals Allanite-(Nd) is visually indistinguishable from other minerals of the allanite subgroup, especially from the much more common allanite-(Ce). It can also be confused with other black, opaque minerals, such as schorl (black tourmaline), ilmenite, or some dark garnets. Definitive differentiation requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS), to confirm the dominance of neodymium. ## Crystal Forms This mineral does not form well-developed crystals. It occurs exclusively as irregular, anhedral grains or in granular aggregates.

Geological environment

## Genesis Allanite-(Nd) forms under very specific geological conditions, in contact metamorphic zones. Its occurrences are associated with xenoliths of crystalline limestones (marbles) that have been incorporated into a serpentinite massif. ## Mineral Associations This mineral co-occurs with other minerals typical of contact-metamorphic rocks. Its most common associations include: vesuvianite, garnets from the andradite-grossular series, diopside, titanite, zircon, and allanite-(Ce). ## Localities The only confirmed locality of allanite-(Nd) in the world is its type locality – the Komatsu quarry, located near the city of Itoigawa, in Niigata Prefecture on Honshu Island, Japan.

Rarity

Very rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of allanite-(Nd) is not assessed in terms of aesthetics in the traditional sense. The most important criterion is the certainty of identification, confirmed by chemical analysis. Specimens rich in allanite-(Nd) are valued, as are those where it co-occurs with well-formed crystals of associated minerals, e.g., vesuvianite or garnet. ## Popular Localities The only source of collector specimens is the type locality in Japan. Material from this location is extremely difficult to obtain and appears on the market very rarely, mainly among specialized collectors of rare minerals and micromounts.

Care and storage

## Cleaning Specimens should be cleaned very carefully, preferably with a soft brush dry to remove dust. If necessary, distilled water can be used, and the specimen gently dried. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral should be protected from contact with strong acids. Due to its brittleness, impacts and sudden temperature changes should be avoided. It is not sensitive to light. ## Storage Specimens, usually micromounts, should be stored in sealed boxes, protecting them from dust and mechanical damage. Like other allanites, it may exhibit trace radioactivity, which should be kept in mind when storing a larger number of specimens.

Sources

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