<prompt> Brown pigment gallstones are formed due to:Cholesterol supersaturationIncreased deconjugation of bilirubin glucuronidesIncreased biliary bilirubin loadIncreased pigment in bile  <response>: Characteristics of different types of gallstones and major risk factors for cholesterol gallstones Cholesterol stones Brown pigment stone Black pigment stone Main composition Cholesterol 50 bilirubin 50 bilirubin Colour Yellow-grey Brown Dark Brown-black Aetiology Cholesterol supersaturation Increased deconjugation of bilirubin glucuronides Increased biliary bilirubin load Ref: J Gastrointestin Liver Dis March 2011 Vol. 20 No 1, 9-11. 