Quartzite is a hard, non-foliated metamorphic rock, pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure related to tectonic compression within orogenic belts. Pure quartzite is white to grey, though quartzites occur in various shades of pink and red due to varying amounts of iron oxide. Other colors, such as yellow, green and orange, are due to other minerals; when sandstone is cemented to quartzite, the individual quartz grains recrystallize along with the former cementing material to form an interlocking mosaic of quartz crystals. Most or all of the original texture and sedimentary structures of the sandstone are erased by the metamorphism; the grainy, sandpaper-like surface becomes glassy in appearance. Minor amounts of former cementing materials, iron oxide, silica and clay migrate during recrystallization and metamorphosis; this causes lenses to form within the quartzite. Orthoquartzite is a pure quartz sandstone composed of well-rounded quartz grains cemented by silica.
Orthoquartzite is 99% SiO2 with only minor amounts of iron oxide and trace resistant minerals such as zircon and magnetite. Although few fossils are present, the original texture and sedimentary structures are preserved; the term is traditionally used for quartz-cemented quartz arenites, both usages are found in the literature. The typical distinction between the two is a metamorphic quartzite is so cemented, diagenetically altered, metamorphosized so that it will fracture and break across grain boundaries, not around them. Quartzite is resistant to chemical weathering and forms ridges and resistant hilltops; the nearly pure silica content of the rock provides little material for soil. In the United States, formations of quartzite can be found in some parts of Pennsylvania, the Washington DC area, eastern South Dakota, Central Texas, southwest Minnesota, Devil's Lake State Park in the Baraboo Range in Wisconsin, the Wasatch Range in Utah, near Salt Lake City, Utah and as resistant ridges in the Appalachians and other mountain regions.
Quartzite is found in the Morenci Copper Mine in Arizona. The town of Quartzsite in western Arizona derives its name from the quartzites in the nearby mountains in both Arizona and Southeastern California. A glassy vitreous quartzite has been described from the Belt Supergroup in the Coeur d’Alene district of northern Idaho. In the United Kingdom, a craggy ridge of quartzite called the Stiperstones runs parallel with the Pontesford-Linley fault, 6 km north-west of the Long Mynd in south Shropshire. To be found in England are the Cambrian "Wrekin quartzite", the Cambrian "Hartshill quartzite". In Wales, Holyhead mountain and most of Holy island off Anglesey sport excellent Precambrian quartzite crags and cliffs. In the Scottish Highlands, several mountains composed of Cambrian quartzite can be found in the far north-west Moine Thrust Belt running in a narrow band from Loch Eriboll in a south-westerly direction to Skye. In Ireland areas of quartzite are found across the northwest, with Errigal in Donegal as the most prominent outcrop.
In continental Europe, various regionally isolated quartzite deposits exist at surface level in a belt from the Rhenish Massif and the German Central Highlands into the Western Czech Republic, for example in the Taunus and Harz mountains. In Poland quartzite deposits at surface level exists in Świętokrzyskie Mountains. In Canada, the La Cloche Mountains in Ontario are composed of white quartzite; the highest mountain in Mozambique, Monte Binga, as well as the rest of the surrounding Chimanimani Plateau are composed of hard, pale grey, Precambrian quartzite. Quartzite is mined in Brazil for use in kitchen countertops; because of its hardness and angular shape, crushed quartzite is used as railway ballast. Quartzite is a decorative stone and may be used to cover walls, as roofing tiles, as flooring, stair steps, its use for countertops in kitchens is expanding rapidly. It is more resistant to stains than granite. Crushed quartzite is sometimes used in road construction. High purity quartzite is used to produce ferrosilicon, industrial silica sand and silicon carbide.
During the Paleolithic, quartzite was used, along with flint and other lithic raw materials, for making stone tools. The term quartzite is derived from German: Quarzit. Neomorphism R. V. Dietrich's GemRocks: Quartzite CSU Pomona Geology: Quartzite Cowen's "The First Geologists" Minnesota Department of Natural Resources: Natural History: Minnesota's geology Wisconsin's Baraboo Syncline South Dakota 2002 Mineral Summary: Production and Environmental Issues Big Sioux River: History of Sioux Falls and Quartzite Photos
The public domain consists of all the creative works to which no exclusive intellectual property rights apply. Those rights may have been forfeited, expressly waived, or may be inapplicable; the works of William Shakespeare and Beethoven, most early silent films, are in the public domain either by virtue of their having been created before copyright existed, or by their copyright term having expired. Some works are not covered by copyright, are therefore in the public domain—among them the formulae of Newtonian physics, cooking recipes, all computer software created prior to 1974. Other works are dedicated by their authors to the public domain; the term public domain is not applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as "under license" or "with permission". As rights vary by country and jurisdiction, a work may be subject to rights in one country and be in the public domain in another; some rights depend on registrations on a country-by-country basis, the absence of registration in a particular country, if required, gives rise to public-domain status for a work in that country.
The term public domain may be interchangeably used with other imprecise or undefined terms such as the "public sphere" or "commons", including concepts such as the "commons of the mind", the "intellectual commons", the "information commons". Although the term "domain" did not come into use until the mid-18th century, the concept "can be traced back to the ancient Roman Law, as a preset system included in the property right system." The Romans had a large proprietary rights system where they defined "many things that cannot be owned" as res nullius, res communes, res publicae and res universitatis. The term res nullius was defined as things not yet appropriated; the term res communes was defined as "things that could be enjoyed by mankind, such as air and ocean." The term res publicae referred to things that were shared by all citizens, the term res universitatis meant things that were owned by the municipalities of Rome. When looking at it from a historical perspective, one could say the construction of the idea of "public domain" sprouted from the concepts of res communes, res publicae, res universitatis in early Roman law.
When the first early copyright law was first established in Britain with the Statute of Anne in 1710, public domain did not appear. However, similar concepts were developed by French jurists in the 18th century. Instead of "public domain", they used terms such as publici juris or propriété publique to describe works that were not covered by copyright law; the phrase "fall in the public domain" can be traced to mid-19th century France to describe the end of copyright term. The French poet Alfred de Vigny equated the expiration of copyright with a work falling "into the sink hole of public domain" and if the public domain receives any attention from intellectual property lawyers it is still treated as little more than that, left when intellectual property rights, such as copyright and trademarks, expire or are abandoned. In this historical context Paul Torremans describes copyright as a, "little coral reef of private right jutting up from the ocean of the public domain." Copyright law differs by country, the American legal scholar Pamela Samuelson has described the public domain as being "different sizes at different times in different countries".
Definitions of the boundaries of the public domain in relation to copyright, or intellectual property more regard the public domain as a negative space. According to James Boyle this definition underlines common usage of the term public domain and equates the public domain to public property and works in copyright to private property. However, the usage of the term public domain can be more granular, including for example uses of works in copyright permitted by copyright exceptions; such a definition regards work in copyright as private property subject to fair-use rights and limitation on ownership. A conceptual definition comes from Lange, who focused on what the public domain should be: "it should be a place of sanctuary for individual creative expression, a sanctuary conferring affirmative protection against the forces of private appropriation that threatened such expression". Patterson and Lindberg described the public domain not as a "territory", but rather as a concept: "here are certain materials – the air we breathe, rain, life, thoughts, ideas, numbers – not subject to private ownership.
The materials that compose our cultural heritage must be free for all living to use no less than matter necessary for biological survival." The term public domain may be interchangeably used with other imprecise or undefined terms such as the "public sphere" or "commons", including concepts such as the "commons of the mind", the "intellectual commons", the "information commons". A public-domain book is a book with no copyright, a book, created without a license, or a book where its copyrights expired or have been forfeited. In most countries the term of protection of copyright lasts until January first, 70 years after the death of the latest living author; the longest copyright term is in Mexico, which has life plus 100 years for all deaths since July 1928. A notable exception is the United States, where every book and tale published prior to 1924 is in the public domain.
Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz, metal oxides and organic matter. Geologic clay deposits are composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, become hard and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. Although many occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, some overlap in particle size and other physical properties; the distinction between silt and clay varies by discipline. Geologists and soil scientists consider the separation to occur at a particle size of 2 µm, sedimentologists use 4–5 μm, colloid chemists use 1 μm.
Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 silt particles as being larger. Mixtures of sand and less than 40% clay are called loam. Loam is used as a building material. Clay minerals form over long periods of time as a result of the gradual chemical weathering of rocks silicate-bearing, by low concentrations of carbonic acid and other diluted solvents; these solvents acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed through hydrothermal activity. There are two types of clay deposits: secondary. Primary clays remain at the site of formation. Secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit. Clay deposits are associated with low energy depositional environments such as large lakes and marine basins.
Depending on the academic source, there are three or four main groups of clays: kaolinite, montmorillonite-smectite and chlorite. Chlorites are not always considered to be a clay, sometimes being classified as a separate group within the phyllosilicates. There are 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals. Varve is clay with visible annual layers, which are formed by seasonal deposition of those layers and are marked by differences in erosion and organic content; this type of deposit is common in former glacial lakes. When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed; the resulting seasonal layering is preserved in an distribution of clay sediment banding. Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway, Northern Ireland, Sweden, it is a sensitive clay, prone to liquefaction, involved in several deadly landslides.
Powder X-ray diffraction can be used to identify clays. The physical and reactive chemical properties can be used to help elucidate the composition of clays. Clays exhibit plasticity. However, when dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur; these changes convert the clay into a ceramic material. Because of these properties, clay is used for making pottery, both utilitarian and decorative, construction products, such as bricks and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware and porcelain. Prehistoric humans discovered the useful properties of clay; some of the earliest pottery shards recovered are from Japan. They are associated with the Jōmon culture and deposits they were recovered from have been dated to around 14,000 BC. Clay tablets were the first known writing medium. Scribes wrote by inscribing them with cuneiform script using a blunt reed called a stylus. Purpose-made clay balls were used as sling ammunition.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, smoking pipes, musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is used in many industrial processes, such as paper making, cement production, chemical filtering; until the late 20th century, bentonite clay was used as a mold binder in the manufacture of sand castings. Clay, being impermeable to water, is used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage. Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification. Traditional uses of clay as medicine goes back to prehistoric times. An example is Armenian bole, used to soothe an upset stomach; some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.
Clay as the defining ingredient of loam is one of the oldest building materials on Earth, among other
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral; the transformation from α-quartz to β-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can induce fracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz. Since antiquity, varieties of quartz have been the most used minerals in the making of jewelry and hardstone carvings in Eurasia; the word "quartz" is derived from the German word "Quarz", which had the same form in the first half of the 14th century in Middle High German in East Central German and which came from the Polish dialect term kwardy, which corresponds to the Czech term tvrdý.
The Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning "icy cold", because some philosophers believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the trigonal crystal system; the ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals form in a'bed' that has unconstrained growth into a void. However, doubly terminated crystals do occur where they develop without attachment, for instance within gypsum. A quartz geode is such a situation where the void is spherical in shape, lined with a bed of crystals pointing inward. Α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221 depending on the chirality.
Β-quartz belongs to space group P6222 and P6422, respectively. These space groups are chiral. Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks; the transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without change in the way they are linked. Although many of the varietal names arose from the color of the mineral, current scientific naming schemes refer to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, has been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, smoky quartz, milky quartz, others; these color differentiation's arise from chromophores which have been incorporated into the crystal structure of the mineral.
Polymorphs of quartz include: α-quartz, β-quartz, moganite, cristobalite and stishovite. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties; the cryptocrystalline varieties are either translucent or opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz including contrasting bands or patterns of color, are agate, carnelian or sard, onyx and jasper. Amethyst is a form of quartz that ranges from a dull purple color; the world's largest deposits of amethysts can be found in Brazil, Uruguay, France and Morocco. Sometimes amethyst and citrine are found growing in the same crystal, it is referred to as ametrine. An amethyst is formed. Blue quartz contains inclusions of fibrous crocidolite. Inclusions of the mineral dumortierite within quartz pieces result in silky-appearing splotches with a blue hue, shades giving off purple and/or grey colors additionally being found.
"Dumortierite quartz" will sometimes feature contrasting light and dark color zones across the material. Interest in the certain quality forms of blue quartz as a collectible gemstone arises in India and in the United States. Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smokey appearance, it is nearly impossible to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much
Cambridge University Press
Cambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by King Henry VIII in 1534, it is the world's oldest publishing house and the second-largest university press in the world, it holds letters patent as the Queen's Printer. The press mission is "to further the University's mission by disseminating knowledge in the pursuit of education and research at the highest international levels of excellence". Cambridge University Press is a department of the University of Cambridge and is both an academic and educational publisher. With a global sales presence, publishing hubs, offices in more than 40 countries, it publishes over 50,000 titles by authors from over 100 countries, its publishing includes academic journals, reference works and English language teaching and learning publications. Cambridge University Press is a charitable enterprise that transfers part of its annual surplus back to the university. Cambridge University Press is both the oldest publishing house in the world and the oldest university press.
It originated from letters patent granted to the University of Cambridge by Henry VIII in 1534, has been producing books continuously since the first University Press book was printed. Cambridge is one of the two privileged presses. Authors published by Cambridge have included John Milton, William Harvey, Isaac Newton, Bertrand Russell, Stephen Hawking. University printing began in Cambridge when the first practising University Printer, Thomas Thomas, set up a printing house on the site of what became the Senate House lawn – a few yards from where the press's bookshop now stands. In those days, the Stationers' Company in London jealously guarded its monopoly of printing, which explains the delay between the date of the university's letters patent and the printing of the first book. In 1591, Thomas's successor, John Legate, printed the first Cambridge Bible, an octavo edition of the popular Geneva Bible; the London Stationers objected strenuously. The university's response was to point out the provision in its charter to print "all manner of books".
Thus began the press's tradition of publishing the Bible, a tradition that has endured for over four centuries, beginning with the Geneva Bible, continuing with the Authorized Version, the Revised Version, the New English Bible and the Revised English Bible. The restrictions and compromises forced upon Cambridge by the dispute with the London Stationers did not come to an end until the scholar Richard Bentley was given the power to set up a'new-style press' in 1696. In July 1697 the Duke of Somerset made a loan of £200 to the university "towards the printing house and presse" and James Halman, Registrary of the University, lent £100 for the same purpose, it was in Bentley's time, in 1698, that a body of senior scholars was appointed to be responsible to the university for the press's affairs. The Press Syndicate's publishing committee still meets and its role still includes the review and approval of the press's planned output. John Baskerville became University Printer in the mid-eighteenth century.
Baskerville's concern was the production of the finest possible books using his own type-design and printing techniques. Baskerville wrote, "The importance of the work demands all my attention. Caxton would have found nothing to surprise him if he had walked into the press's printing house in the eighteenth century: all the type was still being set by hand. A technological breakthrough was badly needed, it came when Lord Stanhope perfected the making of stereotype plates; this involved making a mould of the whole surface of a page of type and casting plates from that mould. The press was the first to use this technique, in 1805 produced the technically successful and much-reprinted Cambridge Stereotype Bible. By the 1850s the press was using steam-powered machine presses, employing two to three hundred people, occupying several buildings in the Silver Street and Mill Lane area, including the one that the press still occupies, the Pitt Building, built for the press and in honour of William Pitt the Younger.
Under the stewardship of C. J. Clay, University Printer from 1854 to 1882, the press increased the size and scale of its academic and educational publishing operation. An important factor in this increase was the inauguration of its list of schoolbooks. During Clay's administration, the press undertook a sizeable co-publishing venture with Oxford: the Revised Version of the Bible, begun in 1870 and completed in 1885, it was in this period as well that the Syndics of the press turned down what became the Oxford English Dictionary—a proposal for, brought to Cambridge by James Murray before he turned to Oxford. The appointment of R. T. Wright as Secretary of the Press Syndicate in 1892 marked the beginning of the press's development as a modern publishing business with a defined editorial policy and administrative structure, it was Wright who devised the plan for one of the most distinctive Cambridge contributions to publishing—the Cambridge Histories. The Cambridge Modern History was published
Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses such as chalks and limestones. Inside the nodule, flint is dark grey, green, white or brown in colour, has a glassy or waxy appearance. A thin layer on the outside of the nodules is different in colour white and rough in texture. From a petrological point of view, "flint" refers to the form of chert which occurs in chalk or marly limestone. "common chert" occurs in limestone. Flint is durable and can be found along streams and beaches, its use to make stone tools dates back millions of years. Due to some properties of flint it breaks into sharp edged pieces making it useful for knife blades and other sharp tools. During the Stone Age access to flint was so important for survival that people would travel or trade to obtain flint. Flint Ridge in eastern Ohio was an important source of flint and Native 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 the Rocky Mountains and south around the Gulf of Mexico. 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 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 hypothesis explains the complex shapes of flint nodules that are found. The source of dissolved silica in the porous media could be the spicules of silicious sponges. Certain types of flint, such as that from the south coast of England, contain trapped fossilised marine flora. Pieces of coral and vegetation have been found preserved like amber inside the flint. Thin slices of the stone reveal this effect. Puzzling giant flint formations known as paramoudra and flint circles are found around Europe but in Norfolk, England on the beaches at Beeston Bump and West Runton.
Flint sometimes occurs in large flint fields for example, in Europe. The "Ohio flint" is the official gemstone of Ohio state, it is formed from limey debris, deposited at the bottom of inland Paleozoic seas hundreds of millions of years ago that hardened into limestone and became infused with silica. The flint from Flint Ridge is found in many hues like red, pink, blue and gray, with the color variations caused by minute impurities of iron compounds. Flint was used in the manufacture of tools during the Stone Age as it splits into thin, sharp splinters called flakes or blades when struck by another hard object; this process is referred to as knapping. The process of making tools this way is called "flintknapping". In Europe, some of the best toolmaking flint has come from Belgium, the coastal chalks of the English Channel, the Paris Basin, Thy in Jutland, the Sennonian deposits of Rügen, Grimes Graves in England, the Upper Cretaceous chalk formation of Dobruja and the lower Danube, the Cenomanian chalky marl formation of the Moldavian Plateau and the Jurassic deposits of the Kraków area and Krzemionki in Poland, as well as of the Lägern in the Jura Mountains of Switzerland.
Flint mining became more common since the Neolithic. In 1938, a project of the Ohio Historical Society, under the leadership of H. Holmes Ellis began to study the flintknapping "methods and techniques" of Native Americans. Like past studies, this work involved experimenting with actual flintknapping 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 include William Henry Holmes, Alonzo W. Pond, Sir Francis H. S. Knowles and Don Crabtree; when struck against steel, a flint edge produces. 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. Prior to the wide availability of steel, rocks of pyrite would be used along with the flint, in a similar way; these methods are popular in woodcraft and amongst people practising traditional fire-starting skills.
A major use of flint and steel was in the flintlock mechanism, used in flintlock firearms, but 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 a hinged piece of steel 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 the percussion cap from the 1840s onward, flintlock rifles and shotguns remain in use amongst recreational shooters. Flint and steel used to strike sparks were superseded by ferrocerium; this man-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