 These modifications predisposed to calcium oxalate crystal formation.However, in 2004, struvite stones once again surpassed calcium oxalate stones 44.9 percent to 44.3 percent, and in 2006, 50 percent of stones were struvite and 39 percent were calcium oxalate.This may have been due to the increased use of diets designed to prevent calcium oxalate crystal formation, which because of increased magnesium in the diet and decreased acidity of the urine help promote struvite crystal formation.