Anorthoyttrialite-(Y)

Chemical formula: Y₄(SiO₄)(Si₃O₁₀)

Anorthoyttrialite-(Y) is an extremely rare yttrium silicate, forming black, resinous masses with high density.

## Characteristics Anorthoyttrialite-(Y) is a very rare mineral from the silicate group, belonging to the sorosilicates. Chemically, it is an yttrium silicate. It occurs as aggregates and masses up to several centimeters in size, rarely forming poorly developed crystals. Its appearance is inconspicuous – typical specimens are black, tar-like masses embedded in the host rock (pegmatite). ## Physical Properties This mineral is characterized by high hardness, reaching 6 on the Mohs scale, and significant density, up to 4.65 g/cm³. It has a strong, resinous to vitreous luster. It is opaque. Due to the content of rare earth elements, it may exhibit weak radioactivity. ## Colors and Varieties Anorthoyttrialite-(Y) is a mineral of uniform, black color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – the dominance of yttrium ("yttrialite") and its crystallographic system – triclinic, or anorthic ("anortho"). The suffix -(Y) indicates that yttrium is the dominant rare earth element in this mineral. It was first described in 1997 by Japanese mineralogists from material originating from the Suishoyama pegmatite in Japan. ## Applications Anorthoyttrialite-(Y) has no industrial applications. Its significance is purely scientific and as a collector's item, as an extremely rare and well-defined mineral.

Properties

Mohs hardness: 6
Luster: Resinous
Streak: Gray
Density: 4.65
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque
Crystal system: Triclinic

Diagnostic features

## Identification Identifying anorthoyttrialite-(Y) in the field is practically impossible without advanced analysis. In a collection, it can be preliminarily identified based on its black color, resinous luster, high density, and occurrence in granitic pegmatites. Definitive identification requires chemical analysis (EDS/WDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other black, resinous pegmatite minerals such as gadolinite, allanite, euxenite, or samarskite. Distinguishing it from these relies on physical properties (anorthoyttrialite-(Y) has a characteristic conchoidal fracture and no cleavage) and, most importantly, on chemical composition and crystal structure. ## Crystal Forms This mineral most often forms irregular, amorphous masses or granular aggregates. Very rarely, poorly developed, tabular crystals of small size are observed, occurring in rock cavities.

Geological environment

## Genesis Anorthoyttrialite-(Y) is a magmatic mineral, crystallizing in the late stage of evolution of granitic pegmatites, rich in rare earth elements, especially yttrium. ## Mineral Associations It usually co-occurs with other pegmatite minerals such as quartz, potassium feldspar (microcline), albite, biotite, as well as rarer minerals containing yttrium and other rare earth elements, e.g., xenotime-(Y), fergusonite-(Y), or gadolinite-(Y). ## Localities The most important and best-studied locality, which is also the type locality, is the Suishoyama pegmatite in Fukushima Prefecture, Japan. Other confirmed occurrences include pegmatites in the Iveland region of Norway and in Sweden.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an anorthoyttrialite-(Y) specimen is assessed primarily based on its identity and provenance. Since this mineral rarely forms well-developed crystals, the greatest value lies in rich concentrations within the host rock or, extremely rarely, visible, even imperfect, crystalline forms. The size of the aggregate also matters. The purity of the specimen and the absence of contamination by other minerals increase its value. ## Popular Localities Specimens from the type locality – the Suishoyama pegmatite in Japan – are most prized by collectors and scientific institutions. Material from Norway is also sought after due to the historical significance of its pegmatites.

Care and storage

## Cleaning Due to its rarity and potential scientific value, cleaning should be limited to an absolute minimum. If necessary, a soft brush can be used to remove loose dust. Water and any chemical agents should be avoided. ## What to Avoid Avoid contact with water, acids, detergents, and other chemicals. The mineral may be sensitive to sudden temperature changes. Although its radioactivity is usually low, caution is advised, and prolonged, close contact should be avoided. ## Storage Specimens of anorthoyttrialite-(Y) should be stored under stable conditions, in a dry place, away from direct sunlight. It is best to keep them in sealed collector boxes, which protect them from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)