[AS., a hard stone.] Amorphous lumps of dark silica which occur in nodular sheets in chalk and other limestones. They often enclose such organisms as shells and sea-urchins; spicules of sponges abound in flint. The process by which flint has been formed is uncertain ; but it is supposed to be due either to the abstraction of silica from sea-water by sponges, or to the decomposition of animal remains. Flint-glass is dispersive of light, and consists of silicate of lead and potassium. It is used for table-ware, and prisms, and is called crystal glass.