A specimen of the very rare mineral ningyoite from the type locality (Ningyo-toge Mine, Tottori Prefecture, Honshu Island, Japan). Ningyoite occurs as almost black crystal aggregates in a small pieces of matrix. — Photo: David Hospital · CC BY-SA 4.0
Ningyoite
Ningyoite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (U,Ca,Ce)₂(PO₄)₂·1-2H₂O.
It crystallizes in the orthorhombic crystal system (space group P222). It is a member of the Rhabdophane structural group.
Key properties: specific gravity 3.3.
IMA symbol Nin, IMA status: approved, named in 1959.
The principal uranium mineral, as coatings and filling cavities in carbonaceous conglomerate (Ningyo mine, Japan); in uranium deposits in organic-rich conglomerate-sandstone-mudstone (British Columbia, Canada).
It is found associated with Pyrite, marcasite, sphalerite, apatite, chlorite, gypsum, quartz, hypersthene, feldspar, clay minerals (Ningyo mine, Japan); saléeite, autunite.
The name refers to Ningyo Pass, Japan, where the mine in which the mineral was first found is located.