Peach pink colored crystals of the extremely rare mineral chiyokoite (IMA 2019-054) from the type and only known locality worldwide, the Fuka mine in Japan (Bitchu-cho, Takahashi, Honshu Island, Japan). Chiyokoite is a complex borate, member of the ettringite group. — Photo: David Hospital · CC BY-SA 4.0
Chiyokoite
Chiyokoite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₃Si(CO₃)[B(OH)₄]O(OH)₅·12H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3). It is a member of the Ettringite structural group.
Key properties: specific gravity 1.85; White streak; Vitreous luster; optically uniaxial.
IMA symbol Cyo, IMA status: approved, named in 2019.
A low-temperature mineral in hydrothermally altered, boron-bearing, low-Fe, calc-silicate skarn.
It is found associated with Calcite, henmilite, tacharanite.
The mineral was named to honor Professor Chiyoko Henmi (1949-2018), Department of Earth Science, Okayama University, Japan.