<prompt> Pigment stone is composed of?Ca bilirubinateCa phosphateCa carbonateCa gluconate  <response>: Ans. a Ca bilirubinateRef: Robbins 9thpg 877Two main types of gallstones:Cholesterol stones most common type in West containing crystalline cholesterol monohydrate.Pigment stones composed mainly of calcium bilirubinate; contain 20 cholesterol and are classified into black brown types, the latter forming secondary to chronic biliary infection. 