Gallstones are stones that form in the gallbladder . Most gallstones are crystals of cholesterol.
Cholesterol is a waxy substance used for many body processes.
Gallstones may also be crystals of calcium and bilirubin. Bilirubin is a by-product formed when red blood cells break down. The gallbladder stores bile. Bile is a liquid produced in the liver that aids in digestion. When a person eats, bile flows through a series of tubes or ducts into the intestines .