Ningyoite

Chemical formula: (U₄+,Ca,Ce₃+)₂(PO₄)₂·₁-₂H₂O

Ningyoite is a rare, radioactive uranium mineral from the phosphate group, found in sedimentary uranium deposits as earthy aggregates and crusts.

## Characteristics Ningyoite is a hydrated phosphate of uranium, calcium, and cerium. It rarely forms discernible crystals, most often occurring as radial aggregates, rosettes, earthy masses, or thin crusts on sedimentary rocks such as sandstones and conglomerates. Its name refers to its discovery location in Japan. ## Physical Properties This mineral has a hardness ranging from 3-4 on the Mohs scale. It is brittle. Due to its uranium content, it is strongly radioactive, which is its key physical characteristic. Its luster is described as earthy or dull. ## Colors and Varieties Ningyoite occurs in shades from brownish-green to brown. No distinct color varieties or commercial varieties are recognized. ## History and Name Ningyoite was first described in 1957 by T. Muto, R. Meyrowitz, A. M. Pommer, and T. Murano. The name comes from its type locality – the Ningyo-toge mine on the border of Tottori and Okayama prefectures in Japan. ## Uses As a uranium mineral, ningyoite is a minor ore of this element. It is primarily of scientific importance and is an object of interest for collectors specializing in rare and radioactive minerals.

Properties

Mohs hardness: 3-4
Luster: Earthy
Density: 0
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification The key diagnostic feature of ningyoite is its strong radioactivity, detectable with a Geiger counter. It occurs in characteristic earthy forms, radial aggregates, or crusts of brownish or brownish-green color in sandy sediments. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals of similar appearance, such as autunite or torbernite; however, these often exhibit more vibrant colors (yellow, green) and clearer fluorescence under UV light. Ningyoite differs from them by the absence or very weak fluorescence and its specific, earthy habit. ## Crystal Forms Well-formed crystals are extremely rare. Fibrous, radial, rosette, as well as massive, earthy, and crust-like aggregates are typical.

Geological environment

## Genesis Ningyoite is a secondary mineral, forming in reducing zones of sedimentary uranium deposits. It forms at low temperatures as a result of the circulation of groundwater, which transports and precipitates uranium in sedimentary rocks, such as sandstones and arkosic conglomerates, often containing organic matter (e.g., charcoal) that acts as a reducing agent. ## Mineral Associations It often co-occurs with other uranium minerals, such as uraninite and coffinite, as well as with pyrite, marcasite, and organic matter. ## Localities The most important and type locality is the Ningyo-toge mine in Japan. It is also known from several other locations worldwide, including uranium deposits in the United States (e.g., Utah and Wyoming).

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the abundance of material on the rock matrix and the form of occurrence are most important. Specimens with clearly visible radial aggregates or rosettes are most valued, as opposed to difficult-to-identify earthy masses. Contrast with a light host rock (sandstone) also enhances visual appeal. ## Popular Localities Undoubtedly, the most classic and sought-after specimens come from the type locality – the Ningyo-toge mine in Japan. These are historically and scientifically most significant.

Care and storage

## Cleaning Ningyoite specimens should generally not be wet cleaned. Dust can be removed very carefully with a soft brush or a low-pressure stream of compressed air. Due to radioactivity, all operations should be performed with extreme caution, avoiding inhalation of dust. ## What to Avoid Contact with water and chemicals should be strictly avoided. The mineral is brittle and susceptible to mechanical damage. As a radioactive mineral, it requires specialized handling – direct, prolonged skin contact should be avoided, and it should be stored away from areas of permanent human presence. ## Storage Ningyoite specimens must be stored in specialized, sealed, and lead-lined containers that isolate radiation. The container should be clearly marked with the international radioactivity symbol. It should be kept in a dry place, away from other minerals that could be damaged by radiation.

External references

https://www.mindat.org/min-2906.html