The gallbladder is a pear shaped organ located on the right side of the abdomen, just below the liver. Gallstones are small, hard deposits that form inside the gallbladder. The size of the gallstone can range from a small grain of sand to a large golf ball. Gallstones are of two types: cholesterol stones and pigment stones. Gallstones can form due to increased amounts of cholesterol or bilirubin; or inadequate emptying of the gallbladder.