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Struvite crystals dog with scale 1.JPG
Crystals of struvite from dog urine
CategoryPhosphate mineral
(repeating unit)
Strunz classification8.CH.40
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupPmn21
ColorColorless, white (dehydrated), yellow or brownish, light gray
Crystal habitEuhedral to platey
TwinningOn {001}
Cleavage{100} perfect
Mohs scale hardness1.5–2
LusterVitreous to dull
DiaphaneityTransparent to translucent
Specific gravity1.7
Optical propertiesBiaxial (+) 2V Measured: 37°
Refractive indexnα = 1.495 nβ = 1.496 nγ = 1.504
Birefringenceδ = 0.009
SolubilitySlightly soluble, dehydrates in dry, warm air
Other characteristicsPyroelectric and piezoelectric

Struvite (magnesium ammonium phosphate) is a phosphate mineral with formula: NH4MgPO4·6H2O. 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 urinary stones and crystals form readily in the urine of animals and humans that are infected with ammonia-producing organisms. They are potentiated by alkaline urine and high magnesium excretion (high magnesium/plant-based diets). They also are potentiated by a specific urinary protein, in domestic cats.


Struvite was first described in 1845 by the German chemist Georg Ludwig Ulex [de] (1811–1883), who found crystals of struvite in what he surmised had once been a medieval midden in Hamburg, Germany ; he named the new mineral after the geographer and geologist Heinrich Christian Gottfried von Struve [de] (1772–1851) of Hamburg.[4][2]


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.[5] A simple test can differentiate struvite from glass.[6]

Use of struvite as an agricultural fertilizer was in fact first described in 1857.

Struvite kidney stones[edit]

Struvite precipitates in alkaline urine, forming kidney stones. Struvite is the most common mineral found in urinary tract stones in dogs,[7] and is found also in urinary tract stones of cats and humans. Struvite stones are potentiated 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.

Even in the absence of infection, accumulation of struvite crystals in the urinary bladder is a problem frequently seen in housecats, with symptoms including difficulty urinating (which may be mistaken for constipation) or blood in the urine (hematuria). The protein cauxin, a protein excreted in large amounts in cat urine that acts to produce a feline pheromone, has recently been found to cause nucleation of struvite crystals in a model system containing the ions necessary to form struvite. This may explain some of the excess struvite production in domestic cats.[8] In the past, surgery has been required to remove struvite uroliths in cats; today, special acidifying low magnesium diets may be used to dissolve sterile struvite stones.[9]

Upper urinary tract stones that involve the renal pelvis and extend into at least 2 calyces are classified as staghorn calculi. Although all types of urinary stones can potentially form staghorn calculi, approximately 75% are composed of a struvite-carbonate-apatite matrix.

Struvite enteroliths[edit]

Struvite is a common mineral found in enteroliths (intestinal concretions) in horses.[10]

Wastewater treatment[edit]

Struvite can be a problem in sewage and waste water treatment, particularly after anaerobic digesters release ammonium and phosphate from waste material. Struvite can form a scale on lines and belts, in centrifuges and pumps, clog system pipes and other equipment including the anaerobic digester itself. Struvite, also referred to as MAP, forms when there is a mole to mole to mole ratio (1:1:1) of magnesium, ammonia and phosphate in the wastewater. The magnesium can be found in soil, seawater as well as drinking water. Ammonia is broken down from the urea in wastewater, and phosphate, which is found through food, soaps and detergents. These elements in place, struvite is more likely to form in a high pH environment, where there is higher conductivity, lower temperatures, and higher concentrations of magnesium, ammonia and phosphate. Recovery of phosphorus from wastestreams as struvite and recycling those nutrients into agriculture as fertilizer appears promising, particularly in agricultural manure and municipal waste water treatment plants.

Having struvite scale in a wastewater treatment system can lead to great inefficiency within the plant or operation due to clogging of the pipes, pumps and equipment. There have been a few options to solve this issue, including replacing the pipes, or using a hydro-jetter or a mechanical grinder to clear them. But many lines can be underground and either of these options implies considerable downtime and labor. Chemical cleaning is now predominately used to clear systems of struvite. Chemical cleaning products have been developed to remove and prevent struvite with minimal downtime. Even a chemical-free, electric method of removing and preventing struvite has been developed and tested successfully at wastewater treatment plants in the USA. The electronic sine wave it produces is sent through the water in the pipe and is therefore effective on underground piping as well. [11] [12][13]


  1. ^ Handbook of mineralogy
  2. ^ a b Webmineral
  3. ^ Mindat
  4. ^ Ulex, G.L. (1845) "On struvite, a new mineral," Memoirs and Proceedings of the Chemical Society, 3 : 106–110.
  5. ^ Connie Thompson (2011-03-10). "Suspected "glass" in canned fish actually natural crystal". Komo News. Retrieved 2016-07-21.
  6. ^
  7. ^ "Uroliths". Shiloh Shepherd Genetic Task Force. February 2014. Retrieved 2014-02-07.
  8. ^ Matsumoto, K.; Funaba, M (February 2008). "Factors affecting struvite (MgNH4PO4·6H2O) crystallization in feline urine". Biochim Biophys Acta. 1780 (2): 233–9. doi:10.1016/j.bbagen.2007.09.013. PMID 17976920.
  9. ^ Smith BHE, Stevenson AE, Markwell PJ. Urinary relative supersaturations of calcium oxalate and struvite in cats are influenced by diet. Journal of Nutrition. 1998;128:2763-2764.
  10. ^ Blue MG, Wittkopp RW (July 1981). "Clinical and structural features of equine enteroliths". Journal of the American Veterinary Medical Association. 179 (1): 79–82. PMID 7251465.
  11. ^ Robert T. Burns; Lara B. Moody; Forbes R. Walker; D. Raj Raman (2001). "Laboratory and In-Situ Reductions of Soluble Phosphorus in Liquid Swine Waste Slurries" (PDF). Environmental Technology. 22 (11): 1273–1278. doi:10.1080/09593332208618190. Archived from the original (PDF) on 2012-03-27. Retrieved 2011-07-16.
  12. ^ Mark Hume. "Sewage plant carries sweet smell of phosphorus". The Globe And Mail. Retrieved 2014-07-08.
  13. ^ Brian Morton. "Reclaiming minerals from waste water to make fertilizer". The Vancouver Sun. Retrieved 2013-06-05.

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