Cholesterol gallstones are due to

Cholesterol is insoluble in water Bile acids and phospholipids in bile keep cholesterol in solution by the formation of micelles An excess of cholesterol relative to bile acids and phospholipids allows cholesterol to form crystals and such bile is called lithogenic bile or supersaturated bile Factors responsible for formation of bile stones Lithogenic bile or supersaturated bile Nucleation (cholesterol monohydrate Crystal aglomerate to become macroscopic crystal) Stasis or GB hypomotility Ref: Sabiston 20th edition Pgno :1492