Struvite

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Struvite crystals

Struvite is an ammonium magnesium phosphate mineral with formula: (NH₄)MgPO₄·6(H₂O). Struvite crystallizes in the orthorhombic system as white to yellowish or brownish-white pyramidal crystals or in platey mica-like forms. It is a soft mineral with Mohs hardness of 1.5 to 2 and has a low specific gravity of 1.7. It is sparingly soluble in neutral and alkaline conditions, but readily soluble in acid.

Struvite occurs as crystallites in urine and as a type of kidney stone (urolith) that is caused by bacterial infection that hydrolyzes urea to ammonium and raises urine pH to neutral or alkaline values. Urea-splitting organisms include Proteus, Pseudomonas, Klebsiella, Staphylococcus, and Mycoplasma. Accumulation of struvite crystals in the bladder is a problem not infrequently seen in housecats, with symptoms including difficulty urinating (which may be mistaken for constipation) or blood in the urine; surgery may be required to remove the crystals. A large struvite stone may be referred to as a Staghorn calculus because it takes the shape of the kidney.

Staghorn calculus

Struvite is occasionally found in canned seafood, where its appearance is that of small glass slivers, objectionable to consumers for aesthetic reasons but of no health consequence. It is also a problem in sewage and waste water treatment, particularly after anaerobic digesters release ammonium and phosphate from waste material, as it forms a scale on lines and clogs system pipes. Recovery of phosphorus from wastestreams as struvite and recycling those nutrients into agriculture as fertilizer appears promising, particularly in agricultural manure and municipal wastewater treatment plants.

Struvite was first described from medieval sewer systems in Hamburg Germany in 1845 and named for geographer and geologist Heinrich Christian Gottfried von Struve (1772-1851). Use as an agricultural fertilizer was first reported in 1857.