Struvite stone is caused by which metal?

Struvite, a crystalline substance is composed of magnesium ammonium phosphate (MgNH4PO4 * 6H2O). Struvite urinary stones have also been referred to as "infection stones" and "triple phosphate" stones. Struvite stones can be caused by alkaline urine, steroid therapy, abnormal retention of urine, a urinary tract infection, or another disorder of the urinary tract. There are five primary types of commonly encountered urinary stones, i.e., calcium oxalate, calcium phosphate, magnesium ammonium phosphate, uric acid, and cystine REF : BAILEY AND LOVE 27TH ED