Uedaite-(Ce)

Chemical formula: Mn₂+Ce₃+Al₂Fe₂+(Si₂O₇)(SiO₄)O(OH)

Uedaite-(Ce) is a rare, black mineral from the epidote group, discovered in Japan, characterized by a complex chemical composition with the presence of cerium.

## Characteristics Uedaite-(Ce) is a complex silicate belonging to the epidote group. It typically forms small, prismatic crystals up to 3 mm long, which can occur as radial aggregates. It is a black mineral with a vitreous luster. Due to its small size and rarity, it is primarily of scientific interest and sought after by specialized collectors. ## Physical Properties Uedaite-(Ce) crystals exhibit a hardness of approximately 6.5 on the Mohs scale. The mineral has a vitreous luster and is opaque. Its calculated density is approximately 4.13 g/cm³. It does not show fluorescence under ultraviolet light. ## Colors and Varieties Uedaite-(Ce) occurs in a uniform, black color. Its streak is grayish. No color varieties or commercial forms are known. ## History and Name The mineral's name honors the Japanese mineralogist and crystallographer, Professor Tadashi Ueda (1919–1988) from Kyoto University, for his contributions to the study of epidote group minerals. The suffix "-(Ce)" refers to the dominant rare-earth element in its composition, which is cerium. The mineral was approved by the International Mineralogical Association (IMA) in 2006, and its discovery was described in 2008. The type locality is the Fuka mine in Okayama Prefecture, Japan. ## Applications Due to its extreme rarity and small crystal size, uedaite-(Ce) has no industrial applications. It serves solely as valuable research material and a collector's item.

Properties

Mohs hardness: 6.5
Luster: Vitreous
Streak: Grayish
Density: 4.13
Cleavage: Good on {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Uedaite-(Ce) is difficult to identify visually without specialized equipment. Its key features include black color, prismatic crystal habit, occurrence in radial aggregates, and vitreous luster. Definitive identification requires advanced analytical methods, such as X-ray microanalysis (EDS/WDS), to confirm its complex chemical composition with a dominance of cerium, manganese, iron, and aluminum. ## Distinguishing from Similar Minerals It can be confused with other black minerals from the epidote group, such as allanite-(Ce) or piemontite. Allanite-(Ce) is often pitch-black and can be slightly radioactive, unlike uedaite-(Ce). Piemontite usually has a reddish or reddish-brown streak, whereas uedaite-(Ce) has a grayish streak. Final differentiation requires chemical analysis. ## Crystal Forms Crystals are prismatic, elongated along the b-axis, reaching up to 3 mm in length. They often form radial or radiating-fibrous aggregates. Twinning has also been observed.

Geological environment

## Genesis Uedaite-(Ce) forms in contact metamorphic zones, within calc-silicate skarns. In its type locality (Fuka mine), it occurs in skarn formed at the contact of biotite granite with Paleozoic carbonate rocks. ## Mineral Associations This mineral coexists with minerals such as: wollastonite, vesuvianite, grossular, diopside, andradite, quartz, calcite, epidote, allanite-(Ce), and chukhrovite-(Ce). ## Localities The only confirmed and described occurrence of uedaite-(Ce) in the world is its type locality – the Fuka mine, near Takahashi City, Okayama Prefecture, on Honshu Island, Japan.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valuable uedaite-(Ce) specimens are those with well-formed, sharply terminated crystals with distinct luster, forming aesthetic, radial aggregates. Due to their small size, the quality of the crystals themselves, rather than the size of the entire specimen, is crucial. Contrast with a light rock matrix (e.g., with wollastonite or quartz) significantly enhances visual appeal and collector value. ## Popular Localities The Fuka mine in Japan is the only source of uedaite-(Ce) specimens. Material from this locality is extremely rare on the collector's market and highly sought after by specialized collectors of rare minerals and systematists.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to the small size of the crystals and their fragility, wet or mechanical cleaning is not recommended to avoid damaging the aggregates. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage the mineral. It should also be protected from ultrasound, high temperatures, and sudden temperature changes. Although it is not light-sensitive, prolonged exposure is not recommended. ## Storage Uedaite-(Ce) specimens, often found on delicate rock matrix, are best stored in sealed "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Avoid storing in areas with high humidity.

Sources

IMA Mineral List (CNMNC)