Flint is a hard rock that ranges in color from brown to dark gray to black. It consists of tiny crystals of the mineral quartz. In most cases, flint occurs as small masses embedded in chalk, limestone, and other rocks. Lighter colored deposits that occur as continuous layers are called chert.
Flint sometimes forms from microscopic organisms that live in water and have shells that contain silica. Silica is a compound of silicon and oxygen, the two elements that make up the mineral quartz. After these organisms die, their shells sink to the bottom of the sea. As time passes, silica dissolves and resolidifies to form flint.
Most flint is so even grained that it can be chipped into smooth, curved flakes. In prehistoric times, people fashioned flint into sharp tools and weapons, such as knives, spears, and arrowheads. Later, people discovered that striking flint against iron or steel produces a spark, and so used flint to start fires. The flintlock firearms that were manufactured from the 1600’s to the mid-1800’s made use of this property.
