Tourmaline is a crystalline boron silicate mineral compounded with elements such as aluminium, magnesium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gemstone comes in a wide variety of colors. According to the Madras Tamil Lexicon the name comes from the Sinhalese word "thoramalli" or "tōra- molli", applied to a group of gemstones found in Sri Lanka. According to the same source, the Tamil "tuvara-malli" and "toramalli" are derived from the Sinhalese root word; this etymology is given in other standard dictionaries including the Oxford English Dictionary. Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a demand for curiosities and gems. At the time, it was not realised that schorl and tourmaline were the same mineral, as it was only about 1703 that it was discovered that some colored gems were not zircons. Tourmaline was sometimes called the "Ceylonese Magnet" because it could attract and repel hot ashes due to its pyroelectric properties.
Tourmalines were used by chemists in the 19th century to polarize light by shining rays onto a cut and polished surface of the gem. Encountered species and varieties: Schorl species: Brownish black to black—schorl,Dravite species: from the Drave district of Carinthia Dark yellow to brownish black—dravite,Elbaite species: named after the island of Elba, Italy Red or pinkish-red—rubellite variety, Light blue to bluish green—Brazilian indicolite variety, Green—verdelite or Brazilian emerald variety, Colorless—achroite variety; the most common species of tourmaline is the sodium iron endmember of the group. It may account for 95% or more of all tourmaline in nature; the early history of the mineral schorl shows that the name "schorl" was in use prior to 1400 because a village known today as Zschorlau was named "Schorl", the village had a nearby tin mine where, in addition to cassiterite, black tourmaline was found. The first description of schorl with the name "schürl" and its occurrence was written by Johannes Mathesius in 1562 under the title "Sarepta oder Bergpostill".
Up to about 1600, additional names used in the German language were "Schurel", "Schörle", "Schurl". Beginning in the 18th century, the name Schörl was used in the German-speaking area. In English, the names shorl and shirl were used in the 18th century. In the 19th century the names common schorl, schörl, schorl and iron tourmaline were the English words used for this mineral. Dravite called brown tourmaline, is the sodium magnesium rich tourmaline endmember. Uvite, in comparison, is a calcium magnesium tourmaline. Dravite forms multiple series, including schorl and elbaite; the name dravite was used for the first time by Gustav Tschermak, Professor of Mineralogy and Petrography at the University of Vienna, in his book Lehrbuch der Mineralogie for magnesium-rich tourmaline from village Dobrova near Unterdrauburg in the Drava river area, Austro-Hungarian Empire. Today this tourmaline locality at Dobrova, is a part of the Republic of Slovenia. Tschermak gave this tourmaline the name dravite, for the Drava river area, the district along the Drava River in Austria and Slovenia.
The chemical composition, given by Tschermak in 1884 for this dravite corresponds to the formula NaMg36B3Si6O27, in good agreement with the endmember formula of dravite as known today. Dravite varieties include the vanadium dravite. A lithium-tourmaline elbaite was one of three pegmatitic minerals from Utö, Sweden, in which the new alkali element lithium was determined in 1818 by Johan August Arfwedson for the first time. Elba Island, was one of the first localities where colored and colorless Li-tourmalines were extensively chemically analysed. In 1850 Karl Friedrich August Rammelsberg described fluorine in tourmaline for the first time. In 1870 he proved. In 1889 Scharitzer proposed the substitution of by F in red Li-tourmaline from Sušice, Czech Republic. In 1914 Vladimir Vernadsky proposed the name Elbait for lithium-, sodium-, aluminum-rich tourmaline from Elba Island, with the simplified formula HAl6B2Si4O21. Most the type material for elbaite was found at Fonte del Prete, San Piero in Campo, Campo nell'Elba, Elba Island, Province of Livorno, Italy.
In 1933 Winchell published an updated formula for elbaite, H8Na2Li3Al3B6Al12Si12O62, used to date written as NaAl633. The first crystal structure determination of a Li-rich tourmaline was published in 1972 by Donnay and Barton, performed on a pink elbaite from San Diego County, United States; the tourmaline mineral group is chemically one of the most complicated groups of silicate minerals. Its composition varies because of isomorphous replacement, its general formula can be written as XY3Z63V3W,where: X = Ca, Na, K, ▢ = vacancy Y = Li, Mg, Fe2+, Mn2+, Zn, Al, Cr3+, V3+, Fe3+, Ti4+, vacancy Z = Mg, Al, Fe3+, Cr3+, V3+ T = Si, Al, B B = B, vacancy V = OH, O W = OH, F, OA revised nomenclature for the tourmaline group was published in 2011. Tourmaline is a six-member ring cyclosilicate having a trigonal crystal system, it occurs
A geologist is a scientist who studies the solid and gaseous matter that constitutes the Earth and other terrestrial planets, as well as the processes that shape them. Geologists study geology, although backgrounds in physics, chemistry and other sciences are useful. Field work is an important component of geology, although many subdisciplines incorporate laboratory work. Geologists work in the energy and mining sectors searching for natural resources such as petroleum, natural gas and base metals, they are in the forefront of preventing and mitigating damage from natural hazards and disasters such as earthquakes, volcanoes and landslides. Their studies are used to warn the general public of the occurrence of these events. Geologists are important contributors to climate change discussions. James Hutton is viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had been supposed to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land.
Hutton published a two-volume version of his ideas in 1795. Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism, the deposition of lava from volcanoes, as opposed to the Neptunists, led by Abraham Werner, who believed that all rocks had settled out of a large ocean whose level dropped over time; the first geological map of the United States was produced in 1809 by William Maclure. In 1807, Maclure commenced the self-imposed task of making a geological survey of the United States; every state in the Union was traversed and mapped by him. The results of his unaided labors were submitted to the American Philosophical Society in a memoir entitled Observations on the Geology of the United States explanatory of a Geological Map, published in the Society's Transactions, together with the nation's first geological map; this antedates William Smith's geological map of England by six years, although it was constructed using a different classification of rocks.
Sir Charles Lyell first published his famous book, Principles of Geology, in 1830. This book, which influenced the thought of Charles Darwin promoted the doctrine of uniformitarianism; this theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not accepted at the time. For an aspiring geologist, training includes significant coursework in physics and chemistry, in addition to classes offered through the geology department. Most geologists need skills in GIS and other mapping techniques. Geology students spend portions of the year the summer though sometimes during a January term and working under field conditions with faculty members. Many non-geologists take geology courses or have expertise in geology that they find valuable to their fields.
Geologists may concentrate their studies or research in one or more of the following disciplines: Economic geology: the study of ore genesis, the mechanisms of ore creation, geostatistics. Engineering geology: application of the geologic sciences to engineering practice for the purpose of assuring that the geologic factors affecting the location, construction and maintenance of engineering works are recognized and adequately provided for. Geochemistry: the applied branch deals with the study of the chemical makeup and behaviour of rocks, the study of the behaviour of their minerals. Geochronology: the study of isotope geology toward determining the date within the past of rock formation, metamorphism and geological events. Geomorphology: the study of landforms and the processes that create them Hydrogeology: the study of the origin and movement of groundwater water in a subsurface geological system. Igneous petrology: the study of igneous processes such as igneous differentiation, fractional crystallization and volcanological phenomena.
Isotope geology: the case of the isotopic composition of rocks to determine the processes of rock and planetary formation. Metamorphic petrology: the study of the effects of metamorphism on minerals and rocks. Marine geology: the study of the seafloor. Marine geology has strong ties to physical plate tectonics. Palaeoclimatology: the application of geological science to determine the climatic conditions present in the Earth's atmosphere within the Earth's history. Palaeontology: the classification and taxonomy of fossils within the geological record and the construction of a palaeontological history of the Earth. Pe
Sand is a granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than coarser than silt. Sand can refer to a textural class of soil or soil type; the composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica in the form of quartz. The second most common type of sand is calcium carbonate, for example, created, over the past half billion years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Sand is a non-renewable resource over human timescales, sand suitable for making concrete is in high demand. Desert sand, although plentiful, is not suitable for concrete, 50 billion tons of beach sand and fossil sand is needed each year for construction; the exact definition of sand varies.
The scientific Unified Soil Classification System used in engineering and geology corresponds to US Standard Sieves, defines sand as particles with a diameter of between 0.074 and 4.75 millimeters. By another definition, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm to 2 mm. An individual particle in this range size is termed a sand grain. Sand grains are between silt; the size specification between sand and gravel has remained constant for more than a century, but particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century. The grains of sand in Archimedes Sand Reckoner written around 240 BCE, were 0.02 mm in diameter. A 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. A 1938 specification of the United States Department of Agriculture was 0.05 mm. Sand feels gritty when rubbed between the fingers.
Silt, by comparison, feels like flour). ISO 14688 grades sands as fine and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is divided into five sub-categories based on size: fine sand, fine sand, medium sand, coarse sand, coarse sand; these sizes are based on the Krumbein phi scale, where size in Φ = -log2D. On this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers; the most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica in the form of quartz, because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering. The composition of mineral sand is variable, depending on the local rock sources and conditions; the bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material, suggesting sand formation depends on living organisms, too.
The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a granitic rock outcrop; some sands contain magnetite, glauconite or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are green in color, as are sands derived from basaltic lava with a high olivine content. Many sands those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones. Rocks erode/weather over a long period of time by water and wind, their sediments are transported downstream; these sediments continue to break apart into smaller pieces. The type of rock the sediment originated from and the intensity of the environment gives different compositions of sand.
The most common rock to form sand is Granite, where the Feldspar minerals dissolve faster than the Quartz, causing the rock to break apart into small pieces. In high energy environments rocks break apart much faster than in more calm settings. For example, Granite rocks this means more Feldspar minerals in the sand because it wouldn't have had time to dissolve; the term for sand formed by weathering is epiclastic. Sand from rivers are collected either from the river itself or its flood plain, accounts for the majority of the sand used in the construction industry; because if this, many small rivers have been depleted, causing environmental concern and economic losses to adjacent land. The rate of sand mining in such areas outweighs the rate the sand can replenish, making it a non-renewable resource. Sand dunes are a consequence of wind deposition; the Sahara Desert is dry because of its geographic location and is known for its vast sand dunes. They exist here because little vegetation is able to grow and there's not a lot of water.
Over time, wind blow
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice. In addition, zinc and calcium species are known; the great range in composition results in considerable variation in physical, X-ray properties. The range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks, hydrothermal rocks and buried sediments; the name chlorite is in reference to its color. They do not contain the element chlorine named from the same Greek root; the typical general formula is: 34O102 · 36. This formula emphasizes the structure of the group. Chlorites have a 2:1 sandwich structure, this is referred to as a talc layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space is composed of 6.
This 6 unit is more referred to as the brucite-like layer, due to its closer resemblance to the mineral brucite. Therefore, chlorite's structure appears as follows: -t-o-t-brucite-t-o-t-brucite... That's why they are called 2:1:1 minerals. An older classification divided the chlorites into two subgroups: the orthochlorites and leptochlorites; the terms are used and the ortho prefix is somewhat misleading as the chlorite crystal system is monoclinic and not orthorhombic. Chlorite is found in igneous rocks as an alteration product of mafic minerals such as pyroxene and biotite. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a metasomatism product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with hydrothermal ore deposits and occurs with epidote, sericite and sulfide minerals. Chlorite is a common metamorphic mineral indicative of low-grade metamorphism.
It is the diagnostic species of the zeolite facies and of lower greenschist facies. It occurs in the quartz, sericite, garnet assemblage of pelitic schist. Within ultramafic rocks, metamorphism can produce predominantly clinochlore chlorite in association with talc. Experiments indicate that chlorite can be stable in peridotite of the Earth's mantle above the ocean lithosphere carried down by subduction, chlorite may be present in the mantle volume from which island arc magmas are generated. Chlorite occurs in a variety of locations and forms. For example, chlorite is found in certain parts of Wales in mineral schists. Chlorite is found in large boulders scattered on the ground surface on Ring Mountain in Marin County, California. Clinoclore and chamosite are the most common varieties. Several other sub-varieties have been described. A massive compact variety of clinochlore used as a decorative carving stone is referred to by the trade name seraphinite, it occurs in the Korshunovskoye iron skarn deposit in the Irkutsk Oblast of Eastern Siberia.
Chlorite is so soft. The powder generated by scratching is green, it feels oily. The plates are not elastic like mica. Talc feels soapy between fingers; the powder generated by scratching is white. Mica plates are elastic. Various types of chlorite stone have been used as raw material for carving into sculptures and vessels since prehistoric times. List of minerals Thuringite Hurlbut CS, Klein C. Manual of Mineralogy. New York: Wiley & Sons. ISBN 0471805807. Grove TL, Chatterjee N, Parman SW, et al.. "The influence of H2O on mantle wedge melting". Earth Planet. Sci. Lett. 249: 74–89. Bibcode:2006E&PSL.249...74G. Doi:10.1016/j.epsl.2006.06.043. "The Mineral Chlorite". Amethyst Galleries. 1996. Archived from the original on 25 Nov 2004. Retrieved 22 Mar 2019. "Chlorite Group: Mineral information and localities". Mindat.org. Retrieved 22 Mar 2019. "Chlorite". Maricopa.edu. Archived from the original on 12 Nov 2014. Retrieved 22 Mar 2019.]
Feldspars are a group of rock-forming tectosilicate minerals that make up about 41% of the Earth's continental crust by weight. Feldspars crystallize from magma as veins in both intrusive and extrusive igneous rocks and are present in many types of metamorphic rock. Rock formed entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are found in many types of sedimentary rocks; the name feldspar derives from the German Feldspat, a compound of the words Feld, "field", Spat meaning "a rock that does not contain ore". The change from Spat to -spar was influenced by the English word spar, meaning a non-opaque mineral with good cleavage. Feldspathic refers to materials; the alternate spelling, has fallen out of use. This group of minerals consists of tectosilicates. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: potassium feldspar endmember KAlSi3O8, albite endmember NaAlSi3O8, anorthite endmember CaAl2Si2O8. Solid solutions between K-feldspar and albite are called "alkali feldspar".
Solid solutions between albite and anorthite are called "plagioclase", or more properly "plagioclase feldspar". Only limited solid solution occurs between K-feldspar and anorthite, in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Albite is considered both alkali feldspar. Alkali feldspars are grouped into two types: those containing potassium in combination with sodium, aluminum, or silicon; the first of these include: orthoclase KAlSi3O8, sanidine AlSi3O8, microcline KAlSi3O8, anorthoclase AlSi3O8. Potassium and sodium feldspars are not miscible in the melt at low temperatures, therefore intermediate compositions of the alkali feldspars occur only in higher temperature environments. Sanidine is stable at the highest temperatures, microcline at the lowest. Perthite is a typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition; the perthitic textures in the alkali feldspars of many granites can be seen with the naked eye.
Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are considered alkali feldspars. Barium feldspars form as the result of the substitution of barium for potassium in the mineral structure; the barium feldspars are monoclinic and include the following: celsian BaAl2Si2O8, hyalophane 4O8. The plagioclase feldspars are triclinic; the plagioclase series follows: albite NaAlSi3O8, oligoclase AlSi2O8, andesine NaAlSi3O8—CaAl2Si2O8, labradorite AlSi2O8, bytownite AlSi2O8, anorthite CaAl2Si2O8. Intermediate compositions of plagioclase feldspar may exsolve to two feldspars of contrasting composition during cooling, but diffusion is much slower than in alkali feldspar, the resulting two-feldspar intergrowths are too fine-grained to be visible with optical microscopes; the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to fine-grained exsolution lamellae.
The specific gravity in the plagioclase series increases from albite to anorthite. Chemical weathering of feldspars results in the formation of clay minerals such as illite and kaolinite. About 20 million tonnes of feldspar were produced in 2010 by three countries: Italy and China. Feldspar is a common raw material used in glassmaking, to some extent as a filler and extender in paint and rubber. In glassmaking, alumina from feldspar improves product hardness and resistance to chemical corrosion. In ceramics, the alkalis in feldspar act as a flux. Fluxes melt at an early stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers and glass fiber. Ceramics and other uses, such as fillers, accounted for the remainder. In earth sciences and archaeology, feldspars are used for K-Ar dating, argon-argon dating, luminescence dating. In October 2012, the Mars Curiosity rover analyzed a rock that turned out to have a high feldspar content.
List of minerals – A list of minerals for which there are articles on Wikipedia List of countries by feldspar production This article incorporates public domain material from the United States Geological Survey document: "Feldspar and nepheline syenite". Bonewitz, Ronald Louis. Rock and Gem. New York: DK Publishing. ISBN 978-0-7566-3342-4. Media related to Feldspar at Wikimedia Commons
Schist is a medium-grade metamorphic rock. Schist has medium to large, sheet-like grains in a preferred orientation, it is defined by having more than 50% platy and elongated minerals finely interleaved with quartz and feldspar. These lamellar minerals include micas, talc, hornblende and others. Quartz occurs in drawn-out grains to such an extent that a particular form called quartz schist is produced. Schist is garnetiferous. Schist has larger grains than phyllite. Geological foliation with medium to large grained flakes in a preferred sheetlike orientation is called schistosity; the names of various schists are derived from their mineral constituents. For example, schists composed of biotite and muscovite are called mica schists. Most schists are mica schists, but graphite and chlorite schists are common. Schists are named for their prominent or unusual mineral constituents, as in the case of garnet schist, tourmaline schist, glaucophane schist; the individual mineral grains in schist, drawn out into flaky scales by heat and pressure, can be seen with the naked eye.
Schist is characteristically foliated, meaning that the individual mineral grains split off into flakes or slabs. The word schist is derived from the Greek word σχίζειν meaning "to split", a reference to the ease with which schists can be split along the plane in which the platy minerals lie. Most schists are derived from clays and muds that have passed through a series of metamorphic processes involving the production of shales and phyllites as intermediate steps. Certain schists are derived from fine-grained igneous rocks such as tuffs. Before the mid-18th century, the terms slate and schist were not differentiated by those involved with mining. During metamorphism, rocks which were sedimentary, igneous or metamorphic are converted into schists and gneisses. If the composition of the rocks was similar, they may be difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, a fine grained feldspathic sandstone, may both be converted into a grey or pink mica-schist.
However, it is possible to distinguish between sedimentary and igneous schists and gneisses. If, for example, the whole district occupied by these rocks has traces of bedding, clastic structure, or unconformability it may be a sign that the original rock was sedimentary. In other cases intrusive junctions, chilled edges, contact alteration or porphyritic structure may prove that in its original condition a metamorphic gneiss was an igneous rock; the last appeal is to the chemistry, for there are certain rock types which occur only as sediments, while others are found only among igneous masses, however advanced the metamorphism may be, it modifies the chemical composition of the mass greatly. Such rocks as limestones, dolomites and aluminous shales have definite chemical characteristics which distinguish them when recrystallized; the schists are classified principally according to the minerals they consist of and on their chemical composition. For example, many metamorphic limestones and calc-schists, with crystalline dolomites, contain silicate minerals such as mica, diopside, scapolite and feldspar.
They are derived from calcareous sediments of different degrees of purity. Another group is rich in quartz, with variable amounts of white and black mica, feldspar and hornblende; these were once arenaceous rocks. The graphitic schists may be believed to represent sediments once containing coal or plant remains. Among schists of igneous origin there are the silky calc-schists, the foliated serpentines, the white mica-schists and banded halleflintas, which have been derived from rhyolites, quartz-porphyries and felsic tuffs; the majority of mica-schists, are altered claystones and shales, pass into the normal sedimentary rocks through various types of phyllite and mica-slates. They are among the most common metamorphic rocks; the diversity in appearance and composition is great, but they form a well-defined group not difficult to recognize, from the abundance of black and white micas and their thin, schistose character. A subgroup is the andalusite-, staurolite-, kyanite- and sillimanite-schists which make their appearance in the vicinity of gneissose granites, have been affected by contact metamorphism.
In geotechnical engineering a schistosity plane forms a discontinuity that may have a large influence on the mechanical behavior of rock masses in, for example, foundation, or slope construction. List of rock textures – A list of rock textural and morphological terms Greenschist Pelite An Examination of Mica Schist by Andrea Samuels, Micscape magazine. Photographs of Manhattan schist. by USGS: Idaho, Univ. of Idaho, articles cited
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of small particules and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes; the particles that form a sedimentary rock are called sediment, may be composed of geological detritus or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, transported to the place of deposition by water, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and piling up on the floor of water bodies. Sedimentation may occur as dissolved minerals precipitate from water solution; the sedimentary rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust.
Sedimentary rocks are only a thin veneer over a crust consisting of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata; the study of sedimentary rocks and rock strata provides information about the subsurface, useful for civil engineering, for example in the construction of roads, tunnels, canals or other structures. Sedimentary rocks are important sources of natural resources like coal, fossil fuels, drinking water or ores; the study of the sequence of sedimentary rock strata is the main source for an understanding of the Earth's history, including palaeogeography and the history of life. The scientific discipline that studies the properties and origin of sedimentary rocks is called sedimentology. Sedimentology is part of both geology and physical geography and overlaps with other disciplines in the Earth sciences, such as pedology, geomorphology and structural geology. Sedimentary rocks have been found on Mars. Sedimentary rocks can be subdivided into four groups based on the processes responsible for their formation: clastic sedimentary rocks, biochemical sedimentary rocks, chemical sedimentary rocks, a fourth category for "other" sedimentary rocks formed by impacts and other minor processes.
Clastic sedimentary rocks are composed of other rock fragments that were cemented by silicate minerals. Clastic rocks are composed of quartz, rock fragments, clay minerals, mica. 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 and mud; the classification of clastic sedimentary rocks parallels this scheme. This tripartite subdivision is mirrored by the broad categories of rudites and lutites in older literature; the subdivision of these three broad categories is based on differences in clast shape, grain size or texture. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel. Sandstone classification schemes vary but most geologists have adopted the Dott scheme, which uses the relative abundance of quartz and lithic framework grains and the abundance of a muddy matrix between the larger grains.
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. Quartz sandstones have >90% quartz grains Feldspathic sandstones have <90% quartz grains and more feldspar grains than lithic grains Lithic sandstones have <90% quartz grains and more lithic grains than feldspar grainsAbundance of muddy matrix material between sand grains When sand-sized particles are deposited, the space between the grains either remains open or is filled with mud. "Clean" sandstones with open pore 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. For example, a quartz arenite would be composed of quartz grains and have little or no clayey matrix between the grains, a lithic wacke would have abundant lithic grains and abundant muddy matrix, etc.
Although the Dott classification scheme is used by sedimentologists, common names like greywacke and quartz sandstone are still used by non-specialists and in popular literature. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles; these fine-grained particles are transported by turbulent flow in water or air, deposited as the flow calms and the particles settle out of suspension. Most authors presently