Gallstones are small stones or lumps, which form in the gallbladder, a small pear-shaped organ located under the liver. The stones form when there is a chemical imbalance inside the gallbladder. People who are overweight or obese are more likely to develop gallstones. There are two main types of gallstones:
- Cholesterol stones are the most common kind, making 80% of gallstones. They are usually yellow-green in color.
- Pigment stones are smaller and darker than cholesterol stones, usually dark brown or black in color. They are made of chemicals that exist in the gallstones, known as bilirubin, which is a fluid your liver makes.