Kimuraite-(Y)

Chemical formula: CaY₂(CO₃)₄·₆H₂O

Kimuraite-(Y) is a rare hydrated calcium yttrium carbonate, forming small, pink or purplish-pink aggregates and tabular crystals.

## Characteristics Kimuraite-(Y) is a rare mineral from the carbonate group, chemically classified as a hydrated calcium yttrium carbonate. It occurs as very small, tabular or bladed crystals, rarely exceeding 1 mm in length. These crystals often form radial aggregates, rosettes, or spherulitic clusters with a silky luster. Due to the small size of the crystals, its features are most often observed under magnification. ## Physical Properties This mineral is characterized by low hardness, approximately 2.5 on the Mohs scale, which means it is very soft and susceptible to scratching. It has a vitreous luster, and on the surfaces of aggregates, often a silky or pearly luster. It is transparent to translucent. Its density is approximately 2.95 g/cm³. ## Colors and Varieties Kimuraite-(Y) occurs in shades from light pink and purplish-pink to almost colorless. Its color is one of its characteristic visual features. No named varieties of this mineral are distinguished. ## History and Name The mineral was first described in 1986 by Japanese mineralogists (J. Nagashima, R. Miyawaki, J. Takase, I. Nakai, K. Ogawa, S. Shibuva, H. Harada). The name honors Ken-ichiro Kimura (1896–1988), retired professor of analytical chemistry at the University of Tokyo, for his contributions to the geochemistry of rare earth elements in Japan. The suffix "-(Y)" in the name indicates the dominance of yttrium among the rare earth elements in its chemical composition. The type locality (locus typicus) is the Kirigo mine in Saga Prefecture, Japan.

Properties

Mohs hardness: 2.5
Luster: Vitreous, Silky, Pearly
Streak: White
Density: 2.95
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Kimuraite-(Y) can be recognized by its characteristic pink or purplish-pink color, silky luster, and typical forms of occurrence – radial aggregates and rosettes composed of very small, tabular crystals. Its low hardness (approx. 2.5) is also an important clue. It reacts with acids, releasing carbon dioxide, but due to the rarity and delicacy of the material, this test is highly inadvisable. ## Distinguishing from Similar Minerals It can be confused with other rare earth carbonates, such as lanthanite-(Y) or tengerite-(Y), which often co-occur with it and have similar forms. Lanthanite-(Y) has a similar habit but is usually white or yellowish. Tengerite-(Y) forms chalky white, earthy coatings. Precise differentiation of these minerals without advanced analytical methods (e.g., XRD, EDS) is practically impossible. ## Crystal Forms Kimuraite-(Y) crystals are very small, usually less than 1 mm in length. They adopt the form of thin tablets or blades with a pseudohexagonal habit. Most often, they form radial, stellar, or spherulitic aggregates and rosettes.

Geological environment

## Genesis Kimuraite-(Y) is a secondary mineral, forming in the weathering zones of granite pegmatites rich in rare earth elements. It forms as a result of low-temperature hydrothermal processes or as a product of alteration of earlier yttrium minerals, such as yttrialite-(Y). ## Mineral Associations This mineral co-occurs with other secondary rare earth carbonates. It is most often accompanied by lanthanite-(Y), tengerite-(Y), lokkaite-(Y), and primary minerals such as yttrialite-(Y), gadolinite-(Y), allanite, and fluorite. ## Localities The most important and best-documented locality, which is also the type locality, is the Kirigo mine in Saga Prefecture, Japan. This mineral has also been identified in several other places worldwide, including Norway (e.g., in pegmatites in the Tørdal area, Telemark), Sweden (Östanmossa mine), and the United States (e.g., Baringer Hill in Texas).

Rarity

Very rare

For collectors

## Quality Criteria The collecting appeal of kimuraite-(Y) primarily depends on the quality and development of its aggregates. Specimens with distinct, well-formed rosettes or radial clusters of intense pink color are most valued. Contrast with the rock matrix and the presence of associated minerals are also important. Due to the microscopic size of the crystals, specimens suitable for viewing under magnification (so-called microminerals) are the standard. ## Popular Localities The most classic and prized specimens come from the type locality – the Kirigo mine in Japan. However, these are extremely rare on the collector's market. Specimens from Norway, though also rare, are sometimes available.

Care and storage

## Cleaning Kimuraite-(Y) specimens are extremely delicate and sensitive. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust particles. Contact with water should be avoided, as the mineral is partially soluble in it. ## What to Avoid Contact with water, acids, and other chemicals that could damage or dissolve it must be strictly avoided. The mineral is very soft, so it must be protected from impacts, abrasions, and contact with harder minerals. High temperatures should also be avoided, as they can lead to its dehydration (loss of water) and destruction of its structure. ## Storage It is recommended to store specimens in sealed, stable containers (e.g., "perky boxes") to protect them from mechanical damage, dust, and humidity changes. Exposure should be away from direct sunlight and heat sources.

Sources

IMA Mineral List (CNMNC)