Calcium oxalate is the most common type of stone and is thought to develop from the precipitation of calcium crystals.
Kidney stones are generally symptomless until they pass into the ureter where they can become lodged and obstruct the flow of urine. The obstruction to flow within the ureters leads to the release of prostaglandins which cause vasodilation of surrounding vessels and stimulate ureteric smooth muscle spasm. Vasodilation of blood vessels promotes a natural diuresis which further places pressure on the kidneys and can lead to distension of the renal capsule - this is what causes the intense pain associated with renal colic.