Gallsontes are crystalline bodies that are formed inside of the body by accretion ("growth or increase in size by gradual external addition") or concretion ("a spherical or ellipsoidal nodule formed by accumulation of mineral matter after deposition of sediment") of normal and abnormal bile components.

The largest single makeup of gallstones are cholesterol stones, which are generally green, but have been found to be white/yellow in color. Cholesterol stones account for approximately 80 percet of all gallstones, and are composed primarily of cholesterol.

The remaining twenty percent is composed of pigment stones. Pigment stones are small, dark stones that are composed of calcium salts that can be found in bile. Both cholesterol stones and pigment stones make up gall stones. There is alot of risks that are apparent with pigment stones such as cirrhosis, biliary tract infections, and hereditary blood cell disorders, such as sickle cell anemia.

Although there is the two distinct stones above, it isn't unusual for stones to exist that are mixed in origin. Gallstones aren't limited to one particular section - they can occur anywhere within the bilary tree. The bilary tree includes the gallbladder and the common bile duct. Gallstones vary greatly in size and numbers. It is possible for the gallbladder to develop one single stone that is as big as golfball, or for it to create several thousand which can be as small as a grain of sand.