1.
The Needles
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The Needles is a row of three distinctive stacks of chalk that rise about 30m out of the sea off the western extremity of the Isle of Wight, United Kingdom, close to Alum Bay. The Needles Lighthouse stands at the outer, western end of the formation, built in 1859, it has been automated since 1994. The formation takes its name from a fourth needle-shaped pillar called Lots Wife, the remaining rocks are not at all needle-like, but the name has stuck. The Needles were featured on the BBC Two TV programme Seven Natural Wonders as one of the wonders of Southern England, the Needles lie just to the southwest of Alum Bay, and are a tourist draw. Scenic boat trips operate from Alum Bay that offer views of the Needles. The rocks and lighthouse have become icons of the Isle of Wight, often photographed by visitors, the main tourist attractions of the headland itself are the two gun batteries, the experimental rocket testing station, and the four Coastguard cottages owned by the National Trust. A branch of the National Coastwatch Institution is also based at the Needles, sited near the New Battery, the Needles – Landmark Attraction situated at the top of the cliff at Alum Bay is a small amusement park. A Chairlift operates between the park and the beach, the Needles were a site of a long-standing artillery battery, from the 1860s to 1954, which was eventually decommissioned. A nearby site on High Down was employed in the testing of rockets for the British ICBM programme, the headland at High Down was used for Black Knight and Black Arrow rocket engine tests from 1956–71. During the peak of activity in the early 1960s some 240 people worked at the complex and these rockets were later used to launch the Prospero X-3 satellite. The site is now owned by the National Trust, and is open to the public, concrete installations remain, but the buildings that were less durable have either been demolished or were torn down by the elements. In 1982, HRH Prince Charles officially opened the restored Needles Old Battery facility, underground rocket testing rooms are currently being restored for exhibition. The first phase of restoration was completed in 2004, the batteries are accessible by car, foot, bicycle, and bus. Though there is a road up to The Old and The New batteries, access is on foot. The battery site becomes dangerous in high winds and is closed to the public in winds above force 8, in the spring and summer, the Southern Vectis bus company sends open-top buses along a route called The Needles Tour. This route approaches the Battery along the edge, using a road reserved for bus traffic. The Needles Tour also has stops in Alum Bay, Totland, Colwell Bay, Fort Victoria, Yarmouth, and Freshwater Bay. The Needles Tour buses are the only allowed on the road from Alum Bay, apart from those owned by National Trust staff or, by prior appointment
2.
Isle of Wight
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The Isle of Wight /ˈaɪl əv ˈwaɪt/ is a county and the largest and second-most populous island in England. It is located in the English Channel, about 4 miles off the coast of Hampshire, the island has resorts that have been holiday destinations since Victorian times, and is known for its mild climate, coastal scenery, and verdant landscape of fields, downland and chines. The island has been home to the poets Swinburne and Tennyson and to Queen Victoria and it has a maritime and industrial tradition including boat building, sail making, the manufacture of flying boats, the hovercraft, and Britains space rockets. The island hosts annual festivals including the Isle of Wight Festival. It has well-conserved wildlife and some of the richest cliffs and quarries for dinosaur fossils in Europe, the Isle was owned by a Norman family until 1293 and was earlier a kingdom in its own right. Rural for most of its history, its Victorian fashionability and the affordability of holidays led to significant urban development during the late 19th. The island was part of Hampshire until 1890 when it became its own administrative county, apart from a shared police force, there is now no administrative link with Hampshire, although a combined local authority with Portsmouth and Southampton is being considered. Until 1995 the island had a governor, the quickest public transport link to the mainland is the hovercraft from Ryde to Southsea, while three ferry and two catamaran services cross the Solent to Southampton, Lymington and Portsmouth. During the Ice Age, sea levels were lower and the Solent was part of a river flowing south east from current day Poole Harbour towards mid-Channel. As sea levels rose, the valley became flooded. The first inhabitants are assumed to have been hunter-gatherers migrating by land during the Paleolithic or Old Stone Age period, as the ice age began to recede. From the Neolithic era onwards, there are indications that the island had wide trading links, with a port at Bouldnor, evidence of Bronze Age tin trading, caesar reported that the Belgae took the Isle of Wight in about 85 BC and gave its name as Vectis. The Roman historian Suetonius mentions that the island was captured by the commander Vespasian, the Romans built no towns or roads on the island, but the remains of at least seven Roman villas have been found, indicating the prosperity of local agriculture. During the Dark Ages the island was settled by Jutes as the kingdom of Wihtwara under King Arwald. In 685 it was invaded by Caedwalla, who tried to replace the inhabitants with his own followers and it suffered especially from Viking raids, and was often used as a winter base by Viking raiders when they were unable to reach Normandy. Later, both Earl Tostig and his brother Harold Godwinson held manors on the island, the Norman Conquest of 1066 created the position of Lord of the Isle of Wight, the island being given by William the Conqueror to his kinsman William FitzOsbern. Carisbrooke Priory and the fort of Carisbrooke Castle were then founded, allegiance was sworn to FitzOsbern rather than the king, the Lordship was subsequently granted to the de Redvers family by Henry I, after his succession in 1100. For nearly 200 years the island was a semi-independent feudal fiefdom, the final private owner was the Countess Isabella de Fortibus, who, on her deathbed in 1293, was persuaded to sell it to Edward I
3.
Southern England Chalk Formation
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The Chalk Formation of Southern England is a system of chalk downland in the south of England. The formation is perhaps best known for Salisbury Plain, the location of Stonehenge, the Isle of Wight, the North Downs are confined chiefly to the counties of Kent and Surrey, and the South to Sussex. The Downs enclose the rich district of the Weald, where the chalk has eroded to form a much flatter landscape, the Berkshire Downs and White Horse Hills adjoin the northernmost part of this formation. The formation called Cranborne Chase is a plateau in central southern England, straddling the counties Dorset. To the north of these downs, mostly in Buckinghamshire, are the Chiltern Hills, at the far south west of the formation are the Dorset Downs, notable for their rich Roman and pre-Roman archaeology, including a number of Iron Age hill forts. The Chalk Formation was laid down under the sea during the Upper Cretaceous period, in south-east England, the chalk deposits were formed into an elongated dome, with the long axis in a roughly east-west direction. Erosion along the line of this removed the central part of the chalk. The remaining chalk forms the characteristic escarpments of the North and South Downs, stronger uplift and folding occurred in Dorset and the Isle of Wight, where the chalk strata are almost vertical in some places, such as The Needles. Chalk stream Uffington White Horse This article incorporates text from a now in the public domain, Chisholm, Hugh
4.
Calcite
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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
5.
Calcium carbonate
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Calcium carbonate is a chemical compound with the formula CaCO3. It is a substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms, snails. Calcium carbonate is the ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale. It is medicinally used as a supplement or as an antacid. Calcium carbonate shares the properties of other carbonates. CaCO3 + CO2 + H2O → Ca2 This reaction is important in the erosion of rock, forming caverns. An unusual form of calcium carbonate is the hexahydrate, ikaite, ikaite is stable only below 6 °C. The vast majority of calcium used in industry is extracted by mining or quarrying. Pure calcium carbonate, can be produced from a quarried source. Alternatively, calcium carbonate is prepared from calcium oxide, other forms can be prepared, the denser, orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite. The aragonite form can be prepared by precipitation at temperatures above 85 °C, calcite contains calcium atoms coordinated by 6 oxygen atoms, in aragonite they are coordinated by 9 oxygen atoms. The vaterite structure is not fully understood, magnesium carbonate MgCO3 has the calcite structure, whereas strontium and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite, aragonite and vaterite are pure calcium carbonate minerals, industrially important source rocks which are predominantly calcium carbonate include limestone, chalk, marble and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate, oyster shells have enjoyed recent recognition as a source of dietary calcium, but are also a practical industrial source. While not practical as a source, dark green vegetables such as broccoli. Beyond Earth, strong evidence suggests the presence of Calcium carbonate on Mars, signs of Calcium Carbonate have been detected at more than one location. This provides some evidence for the past presence of liquid water, Carbonate is found frequently in geologic settings and constitute an enormous carbon reservoir. Calcium carbonate occurs as aragonite, calcite and dolomite, the carbonate minerals form the rock types, limestone, chalk, marble, travertine, tufa, and others
6.
Sedimentary rock
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Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may also occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are also important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geomorphology, geochemistry, sedimentary rocks have also been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, feldspar, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel, sand, and mud and this tripartite subdivision is mirrored by the broad categories of rudites, arenites, and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape, conglomerates and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name. Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
7.
Limestone
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Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate, about 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, most cave systems are through limestone bedrock. The first geologist to distinguish limestone from dolomite was Belsazar Hacquet in 1778, like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts and these organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragment, some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i. e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters and this produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance, the primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters. Limestones may also form in lacustrine and evaporite depositional environments, calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ion concentrations. Calcite exhibits a characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors, especially with weathered surfaces, Limestone may be crystalline, clastic, granular, or massive, depending on the method of formation. Crystals of calcite, quartz, dolomite or barite may line small cavities in the rock, when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams, particularly there are waterfalls. Calcium carbonate is deposited where evaporation of the leaves a solution supersaturated with the chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls, coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the building process, limestone recrystallizes into marble
8.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
9.
Coccolithophore
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A coccolithophore is a unicellular, eukaryotic phytoplankton. Within the Chromalveolata, the coccolithophorids are in the phylum or division Haptophyta, coccolithophorids are distinguished by special calcium carbonate plates of uncertain function called coccoliths, which are also important microfossils. However, there are Prymnesiophyceae species lacking coccoliths, so not every member of Prymnesiophyceae is coccolithophorid, coccolithophores are almost exclusively marine and are found in large numbers throughout the sunlight zone of the ocean. The most abundant species of coccolithophore, Emiliania huxleyi, belongs to the order Isochrysidales and it is found in temperate, subtropical, and tropical oceans. This makes E. huxleyi an important part of the base of a large proportion of marine food webs. It is also the fastest growing coccolithophore in laboratory cultures, coccolithophores are of particular interest to those studying global climate change because as ocean acidity increases, their coccoliths may become even more important as a carbon sink. Furthermore, management strategies are being employed to prevent eutrophication-related coccolithophore blooms, coccolithophores are spherical cells about 5–100 micrometres across, enclosed by calcareous plates called coccoliths, which are about 2–25 micrometres across. Each cell contains two brown chloroplasts which surround the nucleus, each unicellular plankton is enclosed in its own collection of coccoliths, the calcified scales, which make up its exoskeleton or coccosphere. The primary constituent of coccoliths is calcium carbonate, or chalk, calcium carbonate is transparent, so the organisms’ photosynthetic activity is not compromised by encapsulation in a coccosphere. Coccoliths are produced by a process known as coccolithogenesis. Generally, calcification of coccoliths occurs in the presence of light, although not yet entirely understood, the biomineralization process is tightly regulated by calcium signaling. Calcite formation begins in the complex where protein templates nucleate the formation of CaCO3 crystals and complex acidic polysaccharides control the shape. As each scale is produced, it is exported in a Golgi-derived vesicle and this means that the most recently produced coccoliths may lie beneath older coccoliths. Depending upon the stage in the life cycle, two different types of coccoliths may be formed. Holococcoliths are produced only in the phase, lack radial symmetry. These crystals are thought to form at least partially outside the cell, heterococcoliths occur only in the diploid phase, have radial symmetry, and are composed of relatively few complex crystal units. Although they are rare, combination coccospheres, which contain both holococcoliths and heterococcoliths, have observed in the plankton recording coccolithophore life cycle transitions. Finally, the coccospheres of some species are highly modified with various appendages made of specialized coccoliths, while the exact function of the coccosphere is unclear, many potential functions have been proposed
10.
Flint
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Flint is a hard, sedimentary cryptocrystalline form of the mineral quartz, categorized as a variety of chert. It occurs chiefly as nodules and masses in sedimentary rocks, such as chalks, inside the nodule, flint is usually dark grey, black, green, white or brown in colour, and often has a glassy or waxy appearance. A thin layer on the outside of the nodules is usually different in colour, typically white, from a petrological point of view, flint refers specifically to the form of chert which occurs in chalk or marly limestone. Similarly, common chert occurs in limestone, 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 bored by crustaceans or molluscs. This hypothesis certainly explains the shapes of flint nodules that are found. The source of dissolved silica in the media could be the spicules of silicious sponges. Certain types of flint, such as that from the south coast of England, pieces of coral and vegetation have been found preserved like amber inside the flint. Thin slices of the stone often reveal this effect, puzzling giant flint formations known as paramoudra and flint circles are found around Europe but especially in Norfolk, England on the beaches at Beeston Bump and West Runton. Flint sometimes occurs in large flint fields in Jurassic or Cretaceous beds, 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, flint mining is attested since the Palaeolithic, but became more common since the Neolithic. When struck against steel, a flint edge will produce sparks, 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 availability of steel, rocks of pyrite would be used along with the flint. These methods are popular in woodcraft, bushcraft, and among those who wish to use traditional skills, a later, major use of flint and steel was in the flintlock mechanism, used primarily in flintlock firearms, but also used on dedicated fire-starting tools. The sparks ignite the powder and that flame, in turn, ignites the main charge, propelling the ball, bullet. While the military use of the flintlock declined after the adoption of the cap from the 1840s onward, flintlock rifles. Flint and steel used to strike sparks were superseded by ferrocerium and 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 when used correctly, ferrocerium is used in many cigarette lighters, where it is referred to as flint
11.
Chert
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Chert is a fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline silica. Depending on its origin, it can contain either microfossils, small macrofossils, Chert occurs as oval to irregular nodules in greensand, limestone, chalk, and dolostone formations as a replacement mineral, where it is formed as a result of some type of diagenesis. Where it occurs in chalk or marl, it is usually called flint and it also occurs in thin beds, when it is a primary deposit. Thick beds of chert occur in marine deposits. These thickly bedded cherts include the novaculite of the Ouachita Mountains of Arkansas, Oklahoma, the banded iron formations of Precambrian age are composed of alternating layers of chert and iron oxides. Chert also occurs in deposits and is known as diatomaceous chert. Diatomaceous chert consists of beds and lenses of diatomite which were converted during diagenesis into dense, in petrology the term chert is used to refer generally to all rocks composed primarily of microcrystalline, cryptocrystalline and microfibrous quartz. The term does not include quartzite, chalcedony is a microfibrous variety of quartz. Strictly speaking, the flint is reserved for varieties of chert which occur in chalk. Among non-geologists, the distinction between flint and chert is often one of quality - chert being lower quality than flint, among petrologists, chalcedony is sometimes considered separately from chert due to its fibrous structure. Since many cherts contain both microcrystalline and microfibrous quartz, it is difficult to classify a rock as completely chalcedony. The cryptocrystalline nature of chert, combined with its above average ability to resist weathering, recrystallization, for example, The 3.2 Ga chert of the Fig Tree Formation in the Barbeton Mountains between Swaziland and South Africa preserved non-colonial unicellular bacteria-like fossils. The Gunflint Chert of western Ontario preserves not only bacteria and cyanobacteria but also believed to be ammonia-consuming and some that resemble green algae. The Apex Chert of the Pilbara craton, Australia preserved eleven taxa of prokaryotes, the Bitter Springs Formation of the Amadeus Basin, Central Australia, preserves 850 Ma cyanobacteria and algae. The Rhynie chert of Scotland has remains of a Devonian land flora, in prehistoric times, chert was often used as a raw material for the construction of stone tools. Like obsidian, as well as some rhyolites, felsites, quartzites and this results in conchoidal fractures, a characteristic of all minerals with no cleavage planes. When a chert stone is struck against an iron-bearing surface sparks result and this makes chert an excellent tool for starting fires, and both flint and common chert were used in various types of fire-starting tools, such as tinderboxes, throughout history. Cherts are subject to problems when used as concrete aggregates, deeply weathered chert develops surface pop-outs when used in concrete that undergoes freezing and thawing because of the high porosity of weathered chert
12.
Fossil
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Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers is known as the fossil record. The study of fossils across geological time, how they were formed, such a preserved specimen is called a fossil if it is older than some minimum age, most often the arbitrary date of 10,000 years. The observation that fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of dating techniques in the early 20th century allowed geologists to determine the numerical or absolute age of the various strata. Like extant organisms, fossils vary in size from microscopic, even single bacterial cells one micrometer in diameter, to gigantic, such as dinosaurs, Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces. These types of fossil are called trace fossils, as opposed to body fossils, finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals, these are known as chemofossils or biosignatures. The process of fossilization varies according to type and external conditions. Permineralization is a process of fossilization that occurs when an organism is buried, the empty spaces within an organism become filled with mineral-rich groundwater. Minerals precipitate from the groundwater, occupying the empty spaces and this process can occur in very small spaces, such as within the cell wall of a plant cell. Small scale permineralization can produce very detailed fossils, for permineralization to occur, the organism must become covered by sediment soon after death or soon after the initial decay process. The degree to which the remains are decayed when covered determines the later details of the fossil, some fossils consist only of skeletal remains or teeth, other fossils contain traces of skin, feathers or even soft tissues. This is a form of diagenesis, in some cases the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an external mold, if this hole is later filled with other minerals, it is a cast. An endocast or internal mold is formed when sediments or minerals fill the cavity of an organism. This is a form of cast and mold formation. If the chemistry is right, the organism can act as a nucleus for the precipitation of minerals such as siderite, if this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization, replacement occurs when the shell, bone or other tissue is replaced with another mineral
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