One or more tiny, hard particles that form in the duct of one of the salivary glands when chemicals and salts in the saliva become encrusted around a speck of mucus or other solid material. About 80 percent of these stones are found in the salivary glands in the floor of the mouth. When salivary gland stones obstruct the duct, the large amount of saliva produced when food is eaten cannot flow freely into the mouth. The blocked saliva causes the salivary gland to swell and become painful, especially when a person is eating. The pain and swelling may be experienced in front of the ear or under the chin. Salivary gland stones may also contribute to inflammation of the gland.