Imayoshiite
Imayoshiite is an IMA-recognized mineral species in the carbonate class, with the chemical formula Ca₃Al(CO₃)[B(OH)₄](OH)₆·12H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3). It is a member of the Ettringite structural group.
Key properties: Mohs hardness 2–3; specific gravity 1.79; White streak; Vitreous (crystals); silky (aggregates) luster; optically uniaxial.
IMA symbol Iys, IMA status: approved, named in 2013.
Found in cavities in an altered gabbro xenolith in serpentinized dunite, where rims of the xenoliths were hydrothermally altered.
It is found associated with Oyelite, ‘hydrogarnet’, xonotlite, tobermorite, bultfonteinite, apophyllite, prehnite.
The mineral was named to honor the Japanese mineral collector, Takaharu Imayoshi (1905-1984).