Gall stones. Artwork showing gall stones in the gall bladder. The gall bladder (green, left) is a small muscular sac lying under the liver (not seen). It expels bile (a fat emulsifier) into the intestine through the bile duct (tube at right). Gall stones (red) are hard deposits of salts or cholesterol that form in the gall bladder when the chemical composition of bile is upset. They are most common in women, the elderly and the obese. They usually cause no symptoms unless one becomes stuck in the bile duct, which can lead to acute pain, jaundice and infection. Surgical removal of the gall bladder is sometimes necessary.