flint, variety of quartz that commonly occurs in rounded nodules and whose crystal structure is not visible to the naked eye. Flint is dark gray, smoky brown, or black in color; pale gray flint is called chert. When found in chalk or in other rocks containing lime, the nodules frequently have a white coating. Flint is translucent to opaque. It was early used by primitive peoples for making knives and spearheads because, although it is very hard, it is more readily shaped than stone; edges can be flaked off with comparative ease, especially those of freshly dug pieces, by pressure exerted with a piece of stone or bone. Since it is not chipped by pounding, as stone is, sharper edges are obtained. Use of flint tools defines the Stone Age cultures of the Pleistocene epoch. It was long used with steel for lighting fires and later for setting off the powder in flintlock firearms.