Kidney stones form when minerals, such as calcium, form small crystals in the urine. Crystals bind together and form stones, like an oyster forms a pearl from a grain of sand. When a stone becomes dislodged from the kidney, it may become stuck in the ureter, which obstructs the flow of urine. This causes urine to back up into the kidney and the kidney becomes swollen, which causes pain. The most common type of kidney stone is made from calcium and oxalate.

Additional types of types of kidney stones include:

• Uric acid kidney stones
• Cystine kidney stones
• Struvite kidney stones