Calculi are solid concretions of calcium salts or organic compounds, formed in the kidney, bladder, or gall bladder (see gallstones). They are often associated with infection. There may be no symptoms but they may pass down to block tubes, creating severe colic, or obstruction in an organ. They may pass on unaided with antispasm drugs and analgesics, but may require breaking down into smaller pieces with extracorporeal lithotripsy or surgical removal to prevent damage to the kidney or liver.