If the liquid bile contains too much cholesterol, bile salts, or bilirubin, it can harden into stones. The two types of gallstones are cholesterol stones and pigment stones. Cholesterol stones are usually yellow-green and are made primarily of hardened cholesterol. They account for about 80 percent of gallstones. Pigment stones are small, dark stones made of bilirubin.
Gallstones can be as small as a grain of sand or as large as a golf ball.
The gallbladder can develop just one large stone, hundreds of tiny stones, or almost any combination. The gallbladder and the ducts that carry bile and other digestive enzymes from the liver, gallbladder, and pancreas to the small intestine are called the biliary system. Gallstones can block the normal flow of bile if they lodge in any of the ducts that carry bile from the liver to the small intestine. Bile trapped in these ducts can cause inflammation in the gallbladder, the ducts, or, rarely, the liver. Other ducts open into the common bile duct, including the pancreatic duct, which carries digestive enzymes out of the pancreas.