Siwaqaite
Siwaqaite is an IMA-recognized mineral species in the chromate class, with the chemical formula Ca₆Al₂(CrO₄)₃(OH)₁₂·26H₂O.
It crystallizes in the hexagonal crystal system (space group P31c). It is a member of the Ettringite structural group.
Key properties: Mohs hardness 2; specific gravity 1.819; Yellowish gray streak; Vitreous luster; optically uniaxial.
IMA symbol Siw, IMA status: approved, named in 2019.
Found in thin veins and small cavities in spurrite marble of a high-temperature low-pressure pyrometamorphic sequence of rocks.
It is found associated with Calcite, fluorapatite, brownmillerite, minerals of the barite-hashemite series, cuspidine, fluormayenite, gehlenite, perovskite, lakargiite.
The name comes from the name of the locality, Siwaqa area, where the mineral was found.