Gallstones are solid clumps of cholesterol crystals and other substances that may be of variable size. Bile is composed of fatty substances, like cholesterol. When excessive amounts of fat are present, crystals form. Over time, these crystals can combine and form stones. The initial formation of these stones does not cause pain or symptoms. There are different types of gallstones, depending on which fatty substances of the bile has solidified. Also, the stones can vary in size, ranging from a single grain of sand up to the size of a ping-pong ball. About 90% of gallstones are composed of cholesterol.