Kidney stones form when certain minerals and salts in the urine stick together and create solid crystals. The kidneys normally filter blood and produce urine that carries waste products out of the body. When the urine becomes too concentrated or contains too much of certain substances, these particles begin to cluster. Over time they grow from tiny crystals into hard stones. These stones can stay in the kidney or begin moving down the ureter which is when most symptoms appear. Their size can ran