flint

Compact, hard, brittle mineral (a variety of chert), brown, black, or grey in colour, found as nodules in limestone or shale deposits. It consists of cryptocrystalline (grains too small to be visible even under a light microscope) silica, SiO₂, principally in the crystalline form of quartz. Implements fashioned from flint were widely used in prehistory.

The best flint, used for Neolithic tools, is floorstone, a shiny black flint that occurs deep within chalk.

Because of their hardness (7 on the Mohs scale), flint splinters are used for abrasive purposes and, when ground into powder, added to clay during pottery manufacture. Flints have been used for making fire by striking the flint against steel, which produces a spark, and for discharging guns. Flints in cigarette lighters are made from cerium alloy.

Flint

City in southeastern Michigan, USA, on the Flint River, 90 km/56 mi northwest of Detroit; seat of Genesee County; population (2000) 124,900. Car manufacturing is the chief industry here, but this is now in decline. Flint was founded as a trading post in 1819 and laid out in 1836; it was incorporated in 1855.

The city is the site of the University of Michigan at Flint (1956) and the General Motors Institute (1919). In 1886 the Durant-Dort Carriage Company was founded to build horse-drawn carriages. The General Motors Company, founded by William C Durant in 1908, was based here.