Two small single crystals of the extremely rare ammonium phosphate mineral hannayite from the type locality: Skipton Caves, Mount Widderin, Victoria, Australia. — Photo: David Hospital · CC BY-SA 4.0
Hannayite
Hannayite is an IMA-recognized mineral species in the phosphate class, with the chemical formula (NH₄)₂Mg₃(PO₃OH)₄·8H₂O.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: specific gravity 2.03; optically biaxial.
IMA symbol Han, grandfathered status — known before the IMA’s founding, named in 1879.
Occurs as rare druses on guano-derived phosphate mineral crusts in caves.
It is found associated with Biphosphammite, guanine, monetite, syngenite, aphthitalite, struvite, brushite, newberyite, dittmarite, schertelite.
The mineral was named to honor James Ballantine Hannay (1855–1931), Scottish chemist, University of Manchester, Manchester, England.