<prompt> Most common gall bladder stone is?PigmentCholesterolOxalateOxalate  <response>: Cholesterol REF: Harrisons 17th ed chapter 305 Gallstones are formed because of abnormal bile constituents. They are divided into two major types: Cholesterol stones account for 80 of the total, with pigment stones comprising the remaining 20. Cholesterol gallstones usually contain 50 cholesterol monohydrate plus an admixture of calcium salts, bile pigments, proteins, and fatty acids, the latter in brown pigment stones. Pigment stones are composed primarily of calcium bilirubinate; they contain 20 cholesterol and are classified into black and brown types, the latter forming secondary to chronic biliary infection. 