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Formula: (NH4)2Mg3(PO3OH)4.8H2O
Hydrated acid phosphate
Crystal System: Triclinic
Specific gravity: 1.893 measured, 2.03 calculated
Hardness: 2 to 3
Streak: White
Colour: Light yellow, colourless in transmitted light
Solubility: Readily soluble in acids
Environments
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).
Hannayite is an uncommon constutuent of human pathological concretions (kidney stones and the like)
(AM 59.1177–1182).
Localities
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).
Alteration
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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