Flint occurs chiefly asnodules and masses in sedimentary rocks, such aschalks andlimestones.[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. A thin,oxidised layer on the outside of the nodules is usually different in colour, typically white and rough in texture. The nodules can often be found alongstreams andbeaches.
Flint breaks and chips into sharp-edged pieces, making it useful in constructing a variety of cutting tools, such asknife blades and scrapers. The use of flint to makestone tools dates back more than three million years; flint's extremedurability has made it possible to accurately date its use over this time. Flint is one of the primary materials used to define theStone Age.
During the Stone Age, access to flint was so important for survival that people would travel or trade long distances to obtain the stone.Grime's Graves was an important source of flint traded across Europe.Flint Ridge inOhio was another important source of flint, andNative Americans extracted the flint from hundreds of quarries along the ridge. This "Ohio Flint" was traded across the eastern United States, and has been found as far west as theRocky Mountains and south around theGulf of Mexico.[5]
When struck againststeel, flint will produce enough sparks to ignite a fire with the correcttinder, orgunpowder usedin weapons, namely theflintlockfiring mechanism. Although it has been superseded in these uses by different processes (thepercussion cap), or materials (ferrocerium), "flint" has lent its name as generic term for a fire starter.
Silicified remains of algae and silica pseudomorph afterhalite in flint. Pebble of Loire nearMarcigny, France. Image width: about 5 mm
The exact mode of formation of flint is not yet clear, but it is thought that it occurs as a result of chemical changes in compressedsedimentary rock formations during the process ofdiagenesis. Onehypothesis is that a gelatinous material fills cavities in the sediment, such as holes bored bycrustaceans ormolluscs, and that this becomessilicified. This hypothesis would explain the complex shapes of flint nodules that are found. The source of dissolved silica in the porous media could be thespicules of silicious sponges (demosponges).[3] Certain types of flint, such as that from thesouth coast of England and its counterpart on the French side of theChannel, contain trappedfossilised marine flora. Pieces of coral and vegetation have been found preserved inside the flint, similar to the way insects and plant parts are preserved withinamber. Thin slices of the stone often reveal this effect.
Pebble beach made up of flint nodules eroded from the nearbychalk cliffs,Cape Arkona,Rügen, northeast Germany
The "Ohio flint" is the official gemstone of Ohio state. It is formed from limey debris that was deposited at the bottom of inlandPaleozoic seas hundreds of millions of years ago that hardened intolimestone and later became infused withsilica. The flint from Flint Ridge is found in many hues, including red, green, pink, blue, white, and grey, with the colour variations caused by minute impurities ofiron compounds.[7]
Flint can be sandy brown, medium to dark grey, black, reddish brown or an off-white grey in colour.[8]
Neolithic flint axe, about 31 cm longA 12,000 year oldFolsom tradition spearpoint about 76 mm (3 in) long
Flint was used in the manufacture of tools during theStone Age, as it splits into thin, sharp splinters called flakes or blades (depending on the shape) when struck by another hard object (such as ahammerstone made of another material). This process is referred to asknapping.[9]
In 1938, a project of theOhio Historical Society, under the leadership of H. Holmes Ellis began to study the knapping methods and techniques ofNative Americans. Like past studies, this work involved experimenting with actual knapping techniques by creation of stone tools through the use of techniques like direct freehand percussion, freehand pressure and pressure using a rest. Other scholars who have conducted similar experiments and studies includeWilliam Henry Holmes,Alonzo W. Pond,Francis H. S. Knowles andDon Crabtree.[11]
To reduce susceptibility to fragmentation, flint/chert may be heat-treated, being slowly brought up to a temperature of 150 to 260 °C (300 to 500 °F) for 24 hours, then slowly cooled toroom temperature. This makes the material more homogeneous and thus moreknappable and produces tools with a cleaner, sharper cutting edge. Heat treating was known to Stone Age artisans.[citation needed]
A ferrocerium "flint" spark lighter in action[relevant? –discuss]
When struck against steel, a flint edge produces sparks. The hard flint edge shaves off aparticle of the steel that exposes iron, which reacts withoxygen from the atmosphere and can ignite the propertinder.[12]
Prior to the wide availability of steel, rocks ofpyrite (FeS2) would be used along with the flint, in a similar (but more time-consuming) way. These methods remain popular inwoodcraft,bushcraft, and amongst people practising traditional fire-starting skills.[13][14]
A later, major use of flint and steel was in theflintlock mechanism, used primarily inflintlock firearms, but also used on dedicated fire-starting tools. A piece of flint held in the jaws of a spring-loaded hammer, when released by a trigger, strikes ahinged piece of steel ("frizzen") at an angle, creating a shower of sparks and exposing a charge of priming powder. The sparks ignite the priming powder and that flame, in turn, ignites the main charge, propelling the ball, bullet, or shot through the barrel. While the military use of the flintlock declined after the adoption of thepercussion cap from the 1840s onward, flintlock rifles and shotguns remain in use amongst recreational shooters.
Flint and steel used to strike sparks were superseded in the 20th century byferrocerium (sometimes referred to as "flint", although not true flint, "mischmetal", "hot spark", "metal match", or "fire steel"). 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. Because it can produce sparks when wet and can start fires when used correctly, ferrocerium is commonly included insurvival kits. Ferrocerium is used in manylighters, where it is referred to as "a flint".
Flint's utility as a fire starter is hampered by its property of uneven expansion under heating, causing it to fracture, sometimes violently, during heating. This tendency is enhanced by the impurities found in most samples of flint that may expand to a greater or lesser degree than the surrounding stone, and is similar to the tendency ofglass to shatter when exposed to heat, and can become a drawback when flint is used as abuilding material.[15]
Flint, knapped or unknapped, has been used from antiquity (for example at the Late Roman fort ofBurgh Castle in Norfolk) up to the present day as a material for building stone walls, usinglime mortar, and often combined with other available stone orbrick rubble. It was most common in the parts of southern England where no good building stone was available locally, and where brick-making was not widespread until thelate Middle Ages. It is especially associated withEast Anglia, but also used in chalky areas stretching throughHampshire, Sussex,Surrey andKent toSomerset.
Flint was used in the construction of many churches, houses, and other buildings, for example, the large stronghold ofFramlingham Castle. Many different decorative effects have been achieved by using different types of knapping or arrangement and combinations with stone (flushwork), especially in the 15th and early 16th centuries. Because knapping flints to a relatively flush surface and size is a highly skilled process with a high level of wastage, flint finishes typically indicate high status buildings.
DuringWorld War I, in the chalky-soil country of France, the British filledsandbags with flint and used these sandbags asbreastworks.[16]
A flint church – the Parish Church of Saint Thomas, inCricket Saint Thomas, Somerset, England. The height of the very neatly knapped flints varies between 3 and 5 inches (7.6 and 12.7 cm).
Close-up of the wall of the Romanshore fort atBurgh Castle, Norfolk, showing alternating courses of flint andbrick
A typical medieval wall (with modern memorial) atCanterbury Cathedral – knapped and unknapped ("cobble") flints are mixed with pieces of brick and other stones.
Ruins ofThetford Priory show flints and mortar through the whole depth of the wall
Flint pebbles are used as the media in ball mills to grind glazes and other raw materials for theceramics industry.[17] The pebbles are hand-selected based on colour; those having a tint of red, indicating high iron content, are discarded. The remaining blue-grey stones have a low content ofchromophoric oxides and so are lessdeleterious to the colour of the ceramic composition afterfiring.[18]
Bottle kilns traditionally used forcalcining flint
Until recentlycalcined flint was also an important raw material in clay-basedceramic bodies produced in the UK.[19][20] Inclay bodies, calcined flint attenuates the shrinkage whilst drying, and modifies the firedthermal expansion.[21] Flint can also be used inglazes as a network former.[22] In preparation for use flint pebbles, frequently sourced from the coasts of South-East England or Western France, werecalcined to around 1,000 °C (1,800 °F). This heating process both removed organic impurities and induced certain physical reactions, including converting some of the quartz tocristobalite. After calcination the flint pebbles were crushed and milled to a fine particle size.[21][23][24][25] However, the use of flint has now been superseded byquartz.[20] Because of the historical use of flint, the word "flint" is used by some potters (especially in the U.S.) to refer generically to siliceous raw materials used in ceramics that are not flint.[26][27][28]
^Flenniken, J. Jeffrey. "The Past, Present, and Future of Flintknapping: An Anthropological Perspective." Annual Review of Anthropology 13 (1984): 187-203.http://www.jstor.org/stable/2155667Archived 10 September 2020 at theWayback Machine
^Masefield, John, "The Old Frontline," The Macmillan Company, New York, Copyright 1917, pages 34-35.
^Sawyer, J.D. (2007).Thoroughly Modern Milling. American Ceramic Society Bulletin. Vol. Bulletin 86, No. 6.
^Salmang, H.; Francis, M. (1961).Ceramics: Physical and chemical fundamentals. Butterworths.
^Sandeman, E.A. (1921).Notes on the Manufacture of Earthenware. The Technical Press Ltd.
^abSugden, A. (2001). "Changes & developments of non-plastic raw materials".International Ceramics. No. 2.
^abRyan, W.; Radford, C. (1987).Whitewares: Production, testing, and quality control. Pergamon Press.
^'Ceramics Glaze Technology.' Taylor J.R. & Bull A.C. The Institute Of Ceramics & Pergamon Press. 1986.
^"Use of flint in ceramics".Industrial Ceramics. No. 885. 1993.
^Heckroodt, Oelef (March–April 2012). "Silica".Ceramic Review. No. 254. p. 64.
^Manackerman, M.; Davies, E. (1952). Calcination of Flint (Report). Research Paper. Vol. 191 Part 2: Continuous process in a vertical-shaft kiln. British Ceramic Research Association.
^Parmelee, C.W. (1973).Ceramic Glazes (3rd ed.). The Maple Press Company. Dodd, A. (1994).Dictionary of Ceramics (3rd ed.). The Institute of Materials. Hamer, F.; Hamer, J. (2004).The Potter's Dictionary of Materials and Techniques. London, UK: A. & C. Black.
^Marsh, C.M. (1978). "Flint and silica".Proceedings of the American Ceramic Society Annual Meeting 1978; Materials, Equipment, & Whitewares Division.
^Zamek, J. (2005). "Stoneware clay body formulas. Part 2: The perfect body".Ceramics Industry. Vol. 155, no. 10.
^Graves-Brown, Carolyn."AB29 Flint bracelet". Swansea University. Archived fromthe original on 29 October 2012. Retrieved13 January 2011.
