A diet overloaded with the mineral magnesium can trigger magnesium ammonium phosphate crystals in your cat. (purrfectcatdiet.com)
The crystals can be made of magnesium ammonium phosphate (known as struvite) or they can be calcium oxalate. (catbehaviorassociates.com)
After separation of the solid fraction, the released phosphate dissolved in the liquid fraction can be precipitated as magnesium ammonium phosphate and calcium phosphate, which in turn are directly usable as high value fertilising salts. (sciencedaily.com)