Formula: (NH4)2Mg3(PO3OH)4.8H2O

Hydrated acid phosphate
Specific gravity: 1.893
Hardness: 2 to 3
Streak: White
Colour: Light yellow, colourless in transmitted light
Solubility: Readily soluble in acids

Cave deposits

Hannayite occurs as rare druses on guano-derived phosphate mineral crusts in caves. Associated minerals include biphosphammite, guanine, monetite, syngenite, aphthitalite, struvite, brushite, newberyite, dittmarite and schertelite (HOM).


At the type locality, the Skipton Caves, Mount Widderin, Skipton, Corangamite Shire, Victoria, Australia, hannayite is associated with struvite, brushite, newberyite, dittmarite and schertelite (Dana).


Mixtures of the commonly associated minerals hannayite, schertelite, bobierrite, newberyite and struvite may be formed by reaction of magnesium with concentrated ammonium phosphate solutions of the guano deposit, followed by alterations in the course of leaching and aeration. In laboratory preparations, hannayite and schertelite precipitate rapidly from concentrated solutions of ammonium phosphate over the pH range 3.5 to 6 (acid) and the temperature range 25 to 100oC. Newberyite or struvite, depending on the pH, is formed at lower concentrations of ammonium phosphate. When either newberyite or struvite is placed in a saturated solution of monoammonium phosphate, it is replaced by hannayite, which then alters to schertelite in a few days (AM 48.635-641).

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