Flint, occasionally flintstone, is a sedimentary cryptocrystalline form of the mineral quartz,[1][2] categorized as the variety of chert that occurs in chalk or marly limestone.

[3][4] Inside the nodule, flint is usually dark grey or black, green, white, or brown in colour, and has a glassy or waxy appearance.

Flint breaks and chips into sharp-edged pieces, making it useful in constructing a variety of cutting tools, such as knife blades and scrapers.

This "Ohio Flint" was traded across the eastern United States, and has been found as far west as the Rocky Mountains and south around the Gulf of Mexico.

[3] Certain types of flint, such as that from the south coast of England and its counterpart on the French side of the Channel, contain trapped fossilised marine flora.

Pieces of coral and vegetation have been found preserved inside the flint similar to insects and plant parts within amber.

It is formed from limey debris that was deposited at the bottom of inland Paleozoic seas hundreds of millions of years ago that hardened into limestone and later became infused with silica.

[8] Flint was used in the manufacture of tools during the Stone Age as it splits into thin, sharp splinters called flakes or blades (depending on the shape) when struck by another hard object (such as a hammerstone made of another material).

In 1938, a project of the Ohio Historical Society, under the leadership of H. Holmes Ellis began to study the knapping methods and techniques of Native Americans.

Other scholars who have conducted similar experiments and studies include William Henry Holmes, Alonzo W. Pond, Francis H. S. Knowles and Don Crabtree.

The hard flint edge shaves off a particle of the steel that exposes iron, which reacts with oxygen from the atmosphere and can ignite the proper tinder.

This human-made material, when scraped with any hard, sharp edge, produces sparks that are much hotter than obtained with natural flint and steel, allowing use of a wider range of tinders.

It was most common in those parts of southern England where no good building stone was available locally, and where brick-making was not widespread until the later Middle Ages.

[19][20] In clay bodies, calcined flint attenuates the shrinkage whilst drying, and modifies the fired thermal expansion.