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Flint (or flintstone) is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chalcedony or chert. Flint is usually dark-grey, black, or deep brown in colour, and often has a waxy appearance. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones.
The exact mode of formation of flint is not yet clear or agreed but it is thought that it occurs as a result of chemical changes in compressed sedimentary rock formations, during the process of diagenesis. One hypothesis is that a gelatinous material fills cavities in the sediment, such as holes bored by crustaceans or molluscs and that this becomes silicified. This theory certainly explains the complex shapes of flint nodules that are found. The source of dissolved silica in the porous media could arise from the spicules of silicious sponges.
Additional recommended knowledge
Flint was used for the manufacture of flint tools during the Stone Age, as it splits into thin, sharp splinters called flakes or blades (depending in the shape) when struck by another hard object (such as a hammerstone made of another material). This process is referred to as knapping.
In Europe, some of the best toolmaking flint has come from Belgium (Obourg, flint mines of Spiennes), the coastal chalks of the English Channel, the Paris Basin, Thy in Jutland (flint mine at Hov), the Sennonian deposits of Rügen, Grimes Graves in England and the Jurassic deposits of the Kraków-area in Poland. Flint mining is attested since the Palaeolithic, but became more common since the Neolithic (Michelsberg culture, Funnelbeaker culture).
When struck against steel, flint will produce sparks, which when directed onto tinder can be used to start a fire. This occurs when the hard flint knocks off a particle of the steel, which is heated by the impact, and then burns with oxygen from the atmosphere. This method is popular in woodcraft and among campers who want to have an 'authentic' experience. Striking a lump of flint against a piece of steel to make fire is not particularly easy or convenient (although it is much easier than other primitive fire-making methods such as using a bow and drill). Because of this, a similar technology has been miniaturized and integrated into lighters, which are easy to use without skill or practice. The ferrocerium used in these lighters, while sometimes called "flint", works differently from true flint-and-steel, with the steel scraping off slivers of burning ferrocerium, the reverse of traditional flint-and- steel. Starting a fire with flint, however, is a staple of scouting lore.
A later major use was to create the spark that would ignite the powder that would fire a ball or bullet from a flintlock firearm. While the military use of a flintlock declined after the British military generally applied the percussion cap on their muskets in 1842, it is still popular to use the flintlock as a hunting rifle during special muzzleloader seasons or general rifle seasons in several states in the US.
Flint was used extensively from the 13th century until the present day as a material for building stone walls, especially in parts of the UK. In chalky areas, mostly coastal, but also including inland areas such as the North and South Downs in southern England, flint has also been used as a building and walling material, predating the common use of bricks but laid in a similar manner, using lime mortar. For instance, flint was used in the construction of many churches and other buildings in East Anglia, Kent, Sussex and Surrey.
Flint pebbles are used as the media in ball mills to grind glazes and other raw materials for the ceramics industry. The pebbles are hand-selected for colour, with those showing a reddish tint, indicating the presence of iron, being discarded. The remaining blue-grey stones have a low content of chromophoric oxides and so should impart lesser amounts of colouring contaminants.
In the UK, flint pebbles were traditionally an important raw material for clay-based ceramic bodies; after high temperature treatment, to remove organic impurites and induce certain physical reactions, calcined flint performed a similar role to the quartz sand used in other countries, i.e. after milling to fine particle size was the filler component in pottery bodies. Because of this historical use, the term flint is now used by American potters for all siliceous fillers.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Flint". A list of authors is available in Wikipedia.|