Flint (quartz)

Flint (quartz), common massive cryptocrystalline variety of quartz, with a dull, usually dark colour, often found as nodules in chalk deposits. Highest quality flint is from the coastal chalk deposits of Britain and northern France, and poorer grades occur in the Cretaceous limestones of the United States and various other parts of the world.

The presence of microscopic spines of sponges and shells of diatoms in flint suggests that these usually siliceous skeletal structures served as nuclei for the deposition of silica. Flint is a hydrated silica that, under certain conditions, appears to lose water at its surface leaving a thin, porous coating, or patina, of white silica. On the new surfaces of freshly fractured fragments, the flint has a waxy lustre.

Flint breaks with a conspicuous conchoidal fracture, in which the surface is curved and marked by concentric rings, producing sharp edges. Prehistoric peoples found fragments of flint useful for sharp weapons and cutting instruments such as axeheads, arrowheads, and knives. When flint is struck with steel, sparks are readily produced; it was therefore extensively used in the past for igniting tinder and for firing gunpowder in flintlock arms.

Flint is principally used today as an ingredient of fine pottery. The “flints” used in cigarette lighters are an alloy of rare earth elements and iron (misch metal) and have no relation to the quartz flint.