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Formula: (NH4)Mg(PO4).6H2O
Hydrated normal phosphate, struvite group
Crystal System: Orthorhombic
Specific gravity: 1.711 measured, 1.705 calculated
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white (dehydrated), yellow or brownish, light grey; colourless in transmitted light
Solubility: Readily soluble in acids, very slightly soluble in water
Environments
Struvite is typically formed in bird or bat guano in caves and surface deposits, associated with
newberyite, hannayite,
brushite and stercorite
(HOM). It is found as a product of organic decay in putrescent matter, canned foods or other organic matter
(Mindat, Webmin).
Localities
Near Dawson, Yukon, Canada, struvite from the decaying tooth of a mammoth occurs with
newberyite and magnesite
(Dana).
At the type locality, St Nikolai church, Hamburg, Germany, struvite was found in Medieval sewers (Mindat)
in a bed of peat underlying deposits of organic matter
(Dana).
At Paoha Island, Mono Lake, Mono county, California, USA, newberyite
pseudomorphs after struvite have been found
(KL p197).
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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