Types of Kidney Stones and Crystals
Knowing the type of kidney stone or crystal helps determine the cause and may help to reduce the risk of recurrence.
View images of different types of calcium oxalate stones found in the kidneys
Calcium oxalate stones
Calcium oxalate crystals are the most common type of crystal. Approximately 80% of stones are a form of calcium. They are usually made of calcium and oxalate (a natural chemical found in most foods), but are sometimes made of calcium and phosphate.
Oxalate is a naturally occurring substance found in food. Some fruits and vegetables, as well as nuts and chocolate, have high oxalate levels. Your liver also produces oxalate.
Dietary factors, high doses of vitamin D, intestinal bypass surgery and several metabolic disorders can increase the concentration of calcium or oxalate in urine. Calcium crystals may also occur in the form of calcium phosphate.
Other less common stones
Struvite stones
Struvite crystals can happen when you have certain types of urinary tract infections in which bacteria make ammonia that builds up in your urine. Struvite crystals are made of magnesium, ammonium and phosphate. These crystals can grow quickly and become quite large, sometimes with few symptoms or little warning.
Uric acid stones
Uric acid crystals form when your urine is often too acidic. Uric acid can form crystals by itself or with calcium. Uric acid crystals can form in people who don’t drink enough fluids or who lose too much fluid, those who eat a high-protein diet, and those who have gout. Certain genetic factors also may increase your risk of uric acid crystals.
Cystine stones
These crystals form in people with a hereditary disorder that causes the kidneys to excrete too much of certain amino acids (cystinuria).
Other stones
Other, rarer types of crystals also can occur.
