Fractured gallstone. Coloured scanning electron micrograph (SEM) of a fractured gallstone, revealing its internal structure. Gallstones form in the gallbladder, a small organ that stores bile produced by the liver until it is needed. When there is an imbalance in the chemical composition of the bile, cholesterol and bile pigments may crystallise. Over time these crystals can develop into gallstones. Gallstones are usually symptomless unless one obstructs the bile duct, which can cause acute pain, jaundice and infection. Treatment is with drugs to dissolve the stones or surgical removal of the gallbladder. Magnification: x730 when printed 10 centimetres wide.