Flint helped define the Stone Age, yet nobody is sure how it forms
People have been shaping flint into tools for more than three million years, and its toughness means those tools survive to be dated. It starts fires, fired flintlock guns and was traded across half a continent. Yet geologists still cannot say exactly how the stone forms inside chalk.
Chemically flint is silica, a hidden-crystal form of quartz classed as the kind of chert found in chalk or marly limestone. It turns up as nodules that are dark grey, black, brown, green or white inside with a glassy or waxy look, wrapped in a pale, rough outer rind. Nodules often wash out along streams and beaches, and in Norfolk, at Beeston Bump and West Runton, giant formations called paramoudra and flint circles still baffle researchers.
One theory holds that a jelly-like material filled burrows left by crustaceans or molluscs in the seabed sediment and then turned to silica during diagenesis, the slow chemical change of buried sediment. That would explain the knobbly, complex shapes. The silica may have come from the needle-like spicules of sea sponges. Some flint from both sides of the English Channel holds fossil coral and plant matter, preserved much as insects are in amber.
Strike flint with a harder stone and it breaks into thin, razor-edged flakes or blades, a technique called knapping, which made it ideal for knives and scrapers. Mining began in the Paleolithic and spread in the Neolithic; Grimes Graves in England and Krzemionki in Poland were among Europe's prized sources. In North America, Native Americans worked hundreds of quarries along Flint Ridge in Ohio, and that stone travelled as far as the Rocky Mountains and the Gulf of Mexico. Tinted red, pink, blue and green by traces of iron, it is now Ohio's official gemstone. In 1938 an Ohio Historical Society project led by H. Holmes Ellis began recreating Native American knapping methods by hand.
Struck against steel, flint throws off sparks hot enough to light tinder or gunpowder, the principle behind the flintlock. Percussion caps and ferrocerium have since taken over those jobs, but the word flint lives on as a general name for any fire starter.
Source: Flint
