Struvite Stones
Urea is a breakdown product of protein metabolism which is excreted in the urine. Some bacterial urinary track infections convert urea to ammonia making the urine alkaline ( a typical pH of the urine in these infections is 8 or more). The high urine pH increase the risk for struvite stones, which are composed of ammoniomagnesium phosphate.
These stone or visible by X-ray but are less well seen than calcium stones.
The most common bacteria is Proteus but Klebsiella, Pseudomonas, Staphylococci and Serratia also cause these stones.
It is helpful to culture stones if the pH is above 7.