Selwynite
Selwynite is an IMA-recognized mineral species in the phosphate class, with the chemical formula NaKBeZr₂(PO₄)₄·2H₂O.
It crystallizes in the tetragonal crystal system (space group I4_1/amd).
Key properties: Mohs hardness 4; specific gravity 2.94; Pale lavender streak; Vitreous luster; optically uniaxial.
IMA symbol Swy, IMA status: approved, named in 1993.
Very rare, a cavity filling in veins, formed under reducing conditions during late-stage cooling in granite pegmatite.
It is found associated with Wardite, eosphorite, montmorillonite, “limonite”.
The mineral was named to honor Alfred Richard Cecil Selwyn (1824–1902), founding Director of the Geological Survey of Victoria, Australia, and later, the Geological Survey of Canada.
Index entry. This entry combines official IMA/RRUFF species data with published physical-property data — a full written entry hasn’t been published yet.
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