1.
Petrology
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Petrology is the branch of geology that studies the origin, composition, distribution and structure of rocks. In the petroleum industry, lithology, or more specifically mud logging, is the representation of geological formations being drilled through. As the cuttings are circulated out of the borehole they are sampled, examined and tested chemically when needed, Petrology utilizes the fields of mineralogy, petrography, optical mineralogy, and chemical analysis to describe the composition and texture of rocks. Igneous rocks include volcanic and plutonic rocks, sedimentary petrology focuses on the composition and texture of sedimentary rocks. Experiments are particularly useful for investigating rocks of the lower crust and they are also one of the prime sources of information about completely inaccessible rocks such as those in the Earths lower mantle and in the mantles of the other terrestrial planets and the Moon. The work of experimental petrologists has laid a foundation on which modern understanding of igneous, important publications in petrology Ore Soil Best, Myron G. Igneous and Metamorphic Petrology. ISBN 1-4051-0588-7 Blatt, Harvey, Tracy, Robert J. Owens, Brent, Petrology, igneous, sedimentary, ISBN 978-0-7167-3743-8 Dietrich, Richard Vincent, Skinner, Brian J. Gems, Granites, and Gravels, knowing and using rocks and minerals. ISBN 978-0-521-10722-8 Fei, Yingwei, Bertka, Constance M. Mysen, mantle Petrology, field observations and high-pressure experimentation. ISBN 0-941809-05-6 Philpotts, Anthony, Ague, Jay, Principles of Igneous and Metamorphic Petrology
2.
Stratigraphy
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Stratigraphy is a branch of geology which studies rock layers and layering. It is primarily used in the study of sedimentary and layered volcanic rocks, stratigraphy has two related subfields, lithologic stratigraphy or lithostratigraphy, and biologic stratigraphy or biostratigraphy. The first practical application of stratigraphy was by William Smith in the 1790s. Another influential application of stratigraphy in the early 19th century was a study by Georges Cuvier, variation in rock units, most obviously displayed as visible layering, is due to physical contrasts in rock type. This variation can occur vertically as layering, or laterally, and these variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called the law of superposition, states, in a stratigraphic sequence. Chemostratigraphy studies the changes in the proportions of trace elements and isotopes within. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment and this has led to the specialized field of isotopic stratigraphy. Biostratigraphy or paleontologic stratigraphy is based on evidence in the rock layers. Strata from widespread locations containing the fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smiths principle of succession, which predated. It provides strong evidence for the formation and extinction of species, the geologic time scale was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. One important development is the Vail curve, which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns, stratigraphy is also commonly used to delineate the nature and extent of hydrocarbon-bearing reservoir rocks, seals, and traps of petroleum geology. Chronostratigraphy is the branch of stratigraphy that places an absolute age, a gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment, alternatively, the gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity. It is called a hiatus because deposition was on hold for a period of time, a physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus, magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences
3.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
4.
Outcrop
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An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. However, in places where the cover is removed through erosion or tectonic uplift. In Finland, glacial erosion during the last glacial maximum, followed by scouring by sea waves, bedrock and superficial deposits may also be exposed at the Earths surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis, in situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Outcrops are also important for understanding fossil assemblages, paleo-environment. An outcrop example in California is the Vasquez Rocks, familiar from location shooting use in many films, list of rock formations Geological formation Geologic time scale Media related to Outcrops at Wikimedia Commons
5.
Core sample
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A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, the hole made for the core sample is called the core bowling. A variety of core samplers exist to sample different media under different conditions, more continue to be invented on a regular basis. In the coring process, the sample is pushed more or less intact into the tube, removed from the tube in the laboratory, it is inspected and analyzed by different techniques and equipment depending on the type of data desired. Core samples can be taken to test the properties of materials, such as concrete, ceramics, some metals and alloys. Core samples can also be taken of living things, including human beings, the range of equipment and techniques applied to the task is correspondingly great. Core samples are most often taken with their axis oriented roughly parallel to the axis of a borehole. However it is possible to take core samples from the wall of an existing borehole. Taking samples from an exposure, albeit an overhanging rock face or on a different planet, is almost trivial. The penetration forces, if recorded, give information about the strength of different depths in the material and this technique is common in both civil engineering site investigations and geological studies of recent aquatic deposits. The low strength of the materials penetrated means that cores have to be relatively small, vibracoring, in which the sampler is vibrated to allow penetration into thixotropic media. Again, the strength of the subject material limits the size of core that can be retrieved. A mechanism is normally needed to retain the cylindrical sample in the coring tool, the mechanical forces imposed on the core sample by the tool frequently lead to fracture of the core and loss of less-competent intervals, which can greatly complicate interpretation of the core. Cores can routinely be cut as small as a few millimeters in diameter up to over 150 millimeters in diameter, percussion sidewall coring uses robust cylindrical bullets explosively propelled into the wall of a borehole to retrieve a small, short core sample. These tend to be shattered, rendering porosity/ permeability measurements dubious. Many samples can be attempted in a run of the tools. Several tools can often be ganged together for a single run and this is an important consideration in planning sample programmes. Rotary sidewall coring where a miniaturised automated rotary drilling tool is applied to the side of the borehole to cut a sample similar in size to a percussion sidewall core and these tend to suffer less deformation than percussion cores
6.
Lithostratigraphy
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Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology, in general a stratum will be primarily igneous or sedimentary relating to how the rock was formed. Sedimentary layers are laid down by deposition of sediment associated with weathering processes and these layers are distinguishable as having many fossils and are important for the study of biostratigraphy. Igneous layers are either plutonic or volcanic in character depending upon the rate of the rock. These layers are generally devoid of fossils and represent intrusions and volcanic activity occurred over the geologic history of the area. There are a number of principles that are used to explain the appearance of stratum, when an igneous rock cuts across a formation of sedimentary rock, then we can say that the igneous intrusion is younger than the sedimentary rock. The principle of states that a sedimentary rock layer in a tectonically undisturbed stratum is younger than the one beneath. The principle of original horizontality states that the deposition of sediments occurs as essentially horizontal beds, a lithostratigraphic unit conforms to the law of superposition, which state that in any succession of strata, not disturbed or overturned since deposition, younger rocks lies above older rocks. The principle of continuity states that a set of bed extends. Lithostratigraphic units are recognized and defined on the basis of observable rock characteristics, the descriptions of strata based on physical appearance define facies. Lithostratigraphic units are defined by lithic characteristics, and not by age. Stratotype, A designated type of unit consisting of rocks that contain clear-cut characteristics which are representative of a particular lithostratigraphic unit. Lithosome, Masses of rock of essentially uniform character and having interchanging relationships with adjacent masses of different lithology, the fundamental Lithostratigraphic unit is the formation. A formation is a lithologically distinctive stratigraphic unit that is enough to be mappable and traceable. Formations may be subdivided into members and beds and aggregated with other formations into groups and supergroups, two types of contact, conformable and unconformable. Conformable, unbroken deposition, no break or hiatus, the surface strata resulting is called a conformity. Two types of contact between conformable strata, abrupt contacts and gradational contact, the surface stratum resulting is called an unconformity. Four types of unconformity, Angular unconformity, younger sediment lies upon a surface of tilted or folded older rocks
7.
Geologic map
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A geologic map or geological map is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface, stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units and it is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Rock units are represented by colors. Instead of colors, certain symbols can be used, different geologic mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of differing types and ages. Geologists take two major types of measurements, orientations of planes and orientations of lines. Orientations of planes are often measured as a strike and dip, while orientations of lines are measured as a trend. The angle that the bed makes with the horizontal, along the dip direction, is next to the dip line. In the azimuthal system, strike and dip are often given as strike/dip, trend and plunge are used for linear features, and their symbol is a single arrow on the map. The arrow is oriented in the direction of the linear feature and at the end of the arrow. Trend and plunge are often notated as PLUNGE → TREND, the oldest preserved geologic map is the Turin papyrus, which shows the location of building stone and gold deposits in Egypt. The earliest geologic map of the era is the 1771 Map of Part of Auvergne, or figures of, The Current of Lava in which Prisms, Balls. To be used with Mr. Demarests theories of this hard basalt, pasumot and Daily, Geological Engineers of the King. This map is based on Nicolas Desmarests 1768 detailed study of the geology and eruptive history of the Auvergne volcanoes and he identified both landmarks as features of extinct volcanoes. The 1798 report was incorporated in the 1771 Royal Academy of Science compendium, the first geological map of the U. S. was produced in 1809 by William Maclure. In 1807, Maclure undertook the task of making a geological survey of the United States. He traversed and mapped nearly every state in the Union, during the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times. Maclures map shows the distribution of five classes of rock in what are now only the states of the present-day US
8.
Geotechnical investigation
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This type of investigation is called a site investigation. A geotechnical investigation will include surface exploration and subsurface exploration of a site, sometimes, geophysical methods are used to obtain data about sites. Subsurface exploration usually involves soil sampling and laboratory tests of the soil samples retrieved, to obtain information about the soil conditions below the surface, some form of subsurface exploration is required. Methods of observing the soils below the surface, obtaining samples, and determining physical properties of the soils and rocks include test pits, trenching, boring, borings come in two main varieties, large-diameter and small-diameter. Small-diameter borings are frequently used to allow a geologist or engineer to examine soil or rock cuttings or to samples at depth using soil samplers. Soil samples are often categorized as being disturbed or undisturbed, however. Offshore soil collection introduces many difficult variables, in shallow water, work can be done off a barge. In deeper water a ship will be required, deepwater soil samplers are normally variants of Kullenberg-type samplers, a modification on a basic gravity corer using a piston. Seabed samplers are available, which push the collection tube slowly into the soil. Soil samples are taken using a variety of samplers, some provide only disturbed samples, samples can be obtained by digging out soil from the site. Samples taken this way are disturbed samples, trial Pits are relatively small hand or machine excavated tranches used to determine groundwater levels and take disturbed samples from. This sampler typically consists of a cylinder with a cutting edge attached to a rod. The sampler is advanced by a combination of rotation and downward force, samples taken this way are disturbed samples. A method of sampling using an auger as a corkscrew, the auger is screwed into the ground then lifted out. Soil is retained on the blades of the auger and kept for testing, the soil sampled this way is considered disturbed. Utilized in the Standard Test Method for Standard Penetration Test and Split-Barrel Sampling of Soils and this sampler is typically an 18-30 long,2.0 outside diameter hollow tube split in half lengthwise. A hardened metal drive shoe with a 1.375 opening is attached to the end. It is driven into the ground with a 140-pound hammer falling 30, the blow counts required to advance the sampler a total of 18 are counted and reported
9.
Basalt
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Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually characterized as dark, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured and these phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Mars, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
10.
Pillow lava
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Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses and they form the upper part of Layer 2 of normal oceanic crust. Pillow lavas are commonly of basaltic composition, although pillows formed of komatiite, picrite, boninite, in general the more intermediate the composition, the larger the pillows, due to the increase in viscosity of the erupting lava. They occur wherever mafic to intermediate lavas are extruded under water, such as along marine hotspot volcano chains, as new oceanic crust is formed, thick sequences of pillow lavas are erupted at the spreading center fed by dykes from the underlying magma chamber. Pillow lavas and the related sheeted dyke complexes form part of an ophiolite sequence when a segment of oceanic crust is obducted onto continental crust. Pillow lavas are used generally to confirm subaqueous volcanism in metamorphic belts, pillow lavas are also found associated with some subglacial volcanoes at an early stage of an eruption. This process produces a series of interconnecting lobate shapes that are pillow-like in cross-section, the skin cools a lot faster than the inside of the pillow, so it is very fine grained, with a glassy texture. The magma inside the pillow cools more slowly, so is slightly coarser grained than the skin, pillow lavas are used as way-up criterion in geology. The pillow structures will show a convex upper surface, the pillows will have a tapered base downwards as they have moulded to the underlying pillows during their formation. Pillow basalt NeMO Explorer, NOAA - Contains link to video of pillows being formed
11.
Italy
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Italy, officially the Italian Republic, is a unitary parliamentary republic in Europe. Located in the heart of the Mediterranean Sea, Italy shares open land borders with France, Switzerland, Austria, Slovenia, San Marino, Italy covers an area of 301,338 km2 and has a largely temperate seasonal climate and Mediterranean climate. Due to its shape, it is referred to in Italy as lo Stivale. With 61 million inhabitants, it is the fourth most populous EU member state, the Italic tribe known as the Latins formed the Roman Kingdom, which eventually became a republic that conquered and assimilated other nearby civilisations. The legacy of the Roman Empire is widespread and can be observed in the distribution of civilian law, republican governments, Christianity. The Renaissance began in Italy and spread to the rest of Europe, bringing a renewed interest in humanism, science, exploration, Italian culture flourished at this time, producing famous scholars, artists and polymaths such as Leonardo da Vinci, Galileo, Michelangelo and Machiavelli. The weakened sovereigns soon fell victim to conquest by European powers such as France, Spain and Austria. Despite being one of the victors in World War I, Italy entered a period of economic crisis and social turmoil. The subsequent participation in World War II on the Axis side ended in defeat, economic destruction. Today, Italy has the third largest economy in the Eurozone and it has a very high level of human development and is ranked sixth in the world for life expectancy. The country plays a prominent role in regional and global economic, military, cultural and diplomatic affairs, as a reflection of its cultural wealth, Italy is home to 51 World Heritage Sites, the most in the world, and is the fifth most visited country. The assumptions on the etymology of the name Italia are very numerous, according to one of the more common explanations, the term Italia, from Latin, Italia, was borrowed through Greek from the Oscan Víteliú, meaning land of young cattle. The bull was a symbol of the southern Italic tribes and was often depicted goring the Roman wolf as a defiant symbol of free Italy during the Social War. Greek historian Dionysius of Halicarnassus states this account together with the legend that Italy was named after Italus, mentioned also by Aristotle and Thucydides. The name Italia originally applied only to a part of what is now Southern Italy – according to Antiochus of Syracuse, but by his time Oenotria and Italy had become synonymous, and the name also applied to most of Lucania as well. The Greeks gradually came to apply the name Italia to a larger region, excavations throughout Italy revealed a Neanderthal presence dating back to the Palaeolithic period, some 200,000 years ago, modern Humans arrived about 40,000 years ago. Other ancient Italian peoples of undetermined language families but of possible origins include the Rhaetian people and Cammuni. Also the Phoenicians established colonies on the coasts of Sardinia and Sicily, the Roman legacy has deeply influenced the Western civilisation, shaping most of the modern world
12.
Sedimentary
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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
13.
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
14.
Metamorphic rock
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Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means change in form. The original rock is subjected to heat and pressure, causing profound physical and/or chemical change, the protolith may be a sedimentary, an igneous, or even an existing type of metamorphic rock. Metamorphic rocks make up a part of the Earths crust. They are classified by texture and by chemical and mineral assemblage and they may be formed simply by being deep beneath the Earths surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure and they are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earths interior. The study of rocks provides information about the temperatures and pressures that occur at great depths within the Earths crust. Some examples of rocks are gneiss, slate, marble, schist. Metamorphic minerals are those that only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks and these minerals formed during the crystallization of igneous rocks. They are stable at temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are only within certain limits. The change in the size of the rock during the process of metamorphism is called recrystallization. Both high temperatures and pressures contribute to recrystallization, high temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. The layering within metamorphic rocks is called foliation, and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite and this results in a banded, or foliated rock, with the bands showing the colors of the minerals that formed them. Textures are separated into foliated and non-foliated categories, foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a metamorphic rock, originating from shale
15.
Carbonate rock
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Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite. Calcite can be dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH. Calcite exhibits a 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, karst topography and caves develop in carbonate rocks because of their solubility in dilute acidic groundwater. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation, marble is the metamorphic carbonate rock. Rare igneous carbonate rocks exist as intrusive carbonatites and even rarer volcanic carbonate lava
16.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly 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, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an 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, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. 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 mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
17.
Feldspar
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Feldspars are a group of rock-forming tectosilicate minerals that make up about 40% of the Earths continental crust. Feldspars crystallize from magma as veins in both intrusive and extrusive rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of plagioclase feldspar is known as anorthosite. Feldspars are also found in types of sedimentary rocks. The name feldspar derives from the German Feldspat, a compound of the words Feld, field, and Spat, the change from Spat to -spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar, the alternate spelling, felspar, has largely fallen out of use. This group of minerals consists of tectosilicates, solid solutions between albite and anorthite are called plagioclase, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar, the alkali feldspars are as follows, orthoclase —KAlSi3O8 sanidine —AlSi3O8 microcline —KAlSi3O8 anorthoclase —AlSi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a 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 also 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 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 very fine-grained exsolution lamellae, chemical weathering of feldspars results in the formation of clay minerals. About 20 million tonnes of feldspar were produced in 2010, mostly by three countries, Italy, Turkey, and China, Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, in ceramics, the alkalis in feldspar act as a flux, lowering the melting temperature of a mixture. Fluxes melt at a 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, ceramics and other uses, such as fillers, accounted for the remainder
18.
Dunham classification
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Robert J. Dunham published his classification system for limestone in 1962. His scheme focuses on the fabric of carbonate rocks. Dunham divides the rocks into four groups based on relative proportions of coarser clastic particles. Dunham names are essentially for rock families, unlike the Folk classification scheme, Dunham deals with the original porosity of the rock. The Dunham scheme is useful for hand samples because it is based on texture. The classification is a way of describing the composition of rocks in hand sample. Mudstone contains less than 10% grains, supported by a lime mud, wackestone consists of more than 10% grains, supported by a lime mud. Packstone contains lime mud and is grain supported, grainstone lacks mud and is grain supported. Bafflestone develops where organisms have hindered deposition, reducing the local depositional energy and these stones usually contain traces of the baffling organisms, and smaller grains than would be expected from the strength of the paleocurrent. Bindstone is produced where organisms encrust the elements during deposition and bind them together, framestone is a solid calcareous or siliceous framework which is maintained by an organism such as a coral or sponge. Crystalline carbonate does not have recognisable depositional structures, classification of carbonate rocks according to depositional texture. American Association of Petroleum Geologists Memoir
19.
Folk classification
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Folks philosophy is that the name of a rock must convey as much information as possible without being a complete description. For this, he proposed five important properties of sandstones to use as defining characteristics and these five properties are, grain size, chemically precipitated cements, textural maturity, miscellaneous transported constituents, and clan designation. Folks fivefold name must be in the format, However, Folk stated that cements. The other three properties should always be mentioned and these are the main poles of the classification diagram. To define the name one must normalize the sum of abundances of quartz, feldspars. This means that other constituents that dont fit in these categories are disregarded, after this, the relative percentages of quartz, feldspars and rock fragments are used to plot the appropriate point on a QFR triangle and obtain the clan designation. There are some exceptions when summing the abundances, due to the difficulty in distinguishing quartz from metaquartzite rock fragments, metaquartzite is always plotted on the Q pole of the QFR diagram along with quartz. Granites and other igneous rock fragments are plotted in the F pole of the diagram. If there is more plagioclase than there is K-feldspar, the rock is either a plagioclase arkose, a plagioclase subarkose or a lithic plagioclase arkose, respectively. If there is more K-feldspar than there is plagioclase, or if it is too difficult to make a distinction between the feldspars, the name stays as arkose, subarkose or lithic arkose, respectively. If the relative abundances cannot be identified, then the name is simply obtained from the QFR triangle. If the relative abundances can be obtained, one must plot the point in the VRF-MRF-SRF triangle to obtain the clan name. Using this information one must plot the point in the CRF-chert-Ss, Sh triangle, if the relative abundances of different sedimentary rock fragments cannot be obtained, then the rock is called a sedarenite, subsedarenite or feldspathic sedarenite, respectively. The name must be as specific as possible and one must try to avoid using broad terms like litharenite or sedarenite if the information is available. Miscellaneous transported constituents are any grains that do not fall into the categories described by the QFR diagram and these usually include heavy minerals or fossil fragments. These constituents provide a signature for the formation and will help correlating between various samples. Textural maturity is a property that relates to the amount of energy input on transported sediments through the abrasive power of currents. It is observed in certain such as rounding and sorting of the grains
20.
QAPF diagram
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A QAPF diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for Quartz, Alkali feldspar, Plagioclase and these are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized, QAPF diagrams were created by the International Union of Geological Sciences, Subcommission on the Systematics of Igneous Rocks fostered by Albert Streckeisen. Geologists worldwide accept the diagrams as a classification of igneous, especially plutonic rocks, QAPF diagrams are mostly used to classify plutonic rocks, but are also used to classify volcanic rocks if modal mineralogical compositions have been determined. QAPF diagrams are not used to classify pyroclastic rocks or volcanic rocks if modal mineralogical composition is not determined, TAS is also used if volcanic rock contains volcanic glass. QAPF diagrams are not used if mafic minerals make up more than 90% of the rock composition. An exact name can be only if the mineralogical composition is known. The QAPF diagram has four minerals or mineral groups chosen as important cornerstones of the classification and these are quartz, Alkali feldspars, plagioclase feldspars, and feldspathoids. F and Q for chemical reasons can not exist together in one plutonic rock, other minerals may and almost certainly occur in these rocks as well but they have no significance in this classification scheme. So, the diagram is actually composed of two ternary plots. To use the classification, the concentration of minerals must be known. For example, a rock that contains no alkali feldspar and no feldspathoids but contains lots of pyroxenes, plagioclase feldspar. This diagram does not determine whether a rock is gabbro, diorite, there are another criteria used to decide that. Note that this diagram is not used for all plutonic rocks, ultramafic rocks are the most important plutonic rocks that have separate classification diagrams. Classification and Nomenclature of Plutonic Rocks, Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks. IUGS Subcommission on the Systematics of Igneous Rocks, Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Melilite Rocks. Neues Jahrbuch für Mineralogie, Abhandlungen, Vol.141, 1-14, Igneous Rocks, A Classification and Glossary of Terms, Recommendations of International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Classification of Igneous Rocks - IUGS Classification, Geological Sciences Department - Cal Poly Pomona, archived from the original on 30 Sep 2011
21.
Metamorphic facies
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A metamorphic facies is a set of metamorphic mineral assemblages that were formed under similar pressures and temperatures. The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure, Rocks which contain certain minerals can therefore be linked to certain tectonic settings, times and places in the geological history of the area. The boundaries between facies are wide because they are gradational and approximate, the name facies was first used for specific sedimentary environments in sedimentary rocks by Swiss geologist Amanz Gressly in 1838. Analogous with these sedimentary facies a number of metamorphic facies were proposed in 1920 by Finnish petrologist Pentti Eskola, eskolas classification was refined by New-Zealand geologist Francis John Turner throughout his career. A classic work of Turners was the book he published in 1948 titled Mineralogical and Structural Evolution of Metamorphic Rocks, Turner continued to work in the field, refining the metamorphic facies classifications through the end of his career in the early 1970s. The different metamorphic facies are defined by the composition of a rock. When the temperature or pressure in a body change, the rock can cross into a different facies. Whether minerals really react depends on the reaction kinetics, the energy of the reaction. The minerals in a rock and their age relations can be studied by optical microscopy or Scanning Electron Microscopy of thin sections of the rock. Apart from the metamorphic facies of a rock, a terrane can be described by the abbreviations LT, MT, HT, LP, MP. Since the 1980s the term UHP is used for rocks that saw extreme pressures, which minerals grow in a rock is also dependent of the original composition of the protolith. Carbonate rocks have a different composition from say a basalt lava, therefore, a metapsammite and a metapelite will have different mineralogical compositions even though they were in the same metamorphic facies. Every metamorphic facies has some index minerals by which it can be recognized and that does not mean these minerals will necessarily be visible with the naked eye, or even exist in the rock, when the rock did not have the right chemical composition they will not grow. Very typical index minerals are the polymorphs of aluminosilicate, andalusite is stable at low pressure, kyanite is stable at high pressure but relatively low temperature and sillimanite is stable at high temperature. The zeolite facies is the metamorphic facies with the lowest metamorphic grade, at lower temperature and pressure processes in the rock are called diagenesis. The facies is named for zeolites, strongly hydrated tectosilicates and it is named for the minerals prehnite and pumpellyite. The facies is named for the typical texture of the rocks. It is named after amphiboles that form under such circumstances, the depth at which it occurs is not constant
22.
Slate
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Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock, foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. The foliation in slate is called slaty cleavage and it is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression. Slate is frequently grey in color, especially when seen, en masse, Slate is not to be confused with shale, from which it may be formed, or schist. The word slate is used for certain types of object made from slate rock. It may mean a single roofing tile made of slate, or a writing slate and this was traditionally a small smooth piece of the rock, often framed in wood, used with chalk as a notepad or noticeboard, and especially for recording charges in pubs and inns. The phrases clean slate and blank slate come from this usage, before the mid-19th century, the terms slate, shale and schist were not sharply distinguished. In the context of underground mining in the United States. For example, roof slate referred to shale above a coal seam, occasionally, as in the purple slates of North Wales, ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, Slate can be made into roofing slates, a type of roof shingle, or more specifically a type of roof tile, which are installed by a slater. Slate has two lines of breakability – cleavage and grain – which make it possible to split the stone into thin sheets, when broken, slate retains a natural appearance while remaining relatively flat and easy to stack. Slate is particularly suitable as a material as it has an extremely low water absorption index of less than 0. 4%. In fact, this natural slate, which requires only minimal processing, has the lowest embodied energy of all roofing materials, natural slate is used by building professionals as a result of its beauty and durability. Slate is incredibly durable and can last several hundred years, often little or no maintenance. Its low water makes it very resistant to frost damage and breakage due to freezing. Natural slate is also fire resistant and energy efficient, Slate roof tiles are usually fixed either with nails, or with hooks as is common with Spanish slate. In the UK, fixing is typically with double nails onto timber battens or nailed directly onto timber sarking boards, nails were traditionally of copper, although there are modern alloy and stainless steel alternatives. Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 80–100 years, Slate roofs are still used today
23.
Phyllite
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Phyllite is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite, among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden sheen to the surfaces of cleavage, the word comes from the Greek phyllon, meaning leaf. The protolith for phyllite is shale or pelite, or slate and its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a texture called phyllitic sheen, and are classified as having formed through low-grade metamorphic conditions through regional metamorphism metamorphic facies. Phyllites are usually black to gray or light gray in color. The foliation is commonly crinkled or wavy in appearance, phyllite is commonly found in the Dalradian metasediments of northwest Arran. In north Cornwall, there are Tredorn phyllites and Woolgarden phyllites
24.
Schist
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Schist is a medium-grade metamorphic rock with medium to large, flat, sheet-like grains in a preferred orientation. It is defined by having more than 50% platy and elongated minerals, often finely interleaved with quartz and these lamellar minerals include micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a form called quartz schist is produced. Schist forms at a temperature and has larger grains than phyllite. Geological foliation with medium to large grained flakes in a preferred orientation is called schistosity. The names of various schists are derived from their mineral constituents, for example, schists rich in mica are called mica schists and include biotite or muscovite. Most schists are mica schists, but graphite and chlorite schists are also common, Schists are also named for their prominent or perhaps unusual mineral constituents, as in the case of garnet schist, tourmaline schist, and glaucophane schist. The individual mineral grains in schist, drawn out into flaky scales by heat and pressure, Schist is characteristically foliated, meaning that the individual mineral grains split off easily into flakes or slabs. Most schists are derived from clays and muds that have passed through a series of processes involving the production of shales, slates and phyllites as intermediate steps. Certain schists are derived from fine-grained igneous rocks such as basalts, before the mid-18th century, the terms slate, shale and schist were not sharply differentiated by those involved with mining. In the context of underground mining, shale was frequently referred to as slate well into the 20th century. During metamorphism, rocks which were originally sedimentary, igneous or metamorphic are converted into schists, if the composition of the rocks was originally similar, they may be very difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, and a fine grained feldspathic sandstone, usually, however, it is possible to distinguish between sedimentary and igneous schists and gneisses. If, for example, the district occupied by these rocks has traces of bedding, clastic structure, or unconformability. 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. Such rocks as limestones, dolomites, quartzites and aluminous shales have very definite chemical characteristics which distinguish them even when completely recrystallized, the schists are classified principally according to the minerals they consist of and on their chemical composition. For example, many metamorphic limestones, marbles, and calc-schists, with crystalline dolomites, contain silicate minerals such as mica, tremolite, diopside, scapolite, quartz and they are derived from calcareous sediments of different degrees of purity. Another group is rich in quartz, with amounts of white and black mica, garnet, feldspar, zoisite
25.
Gneiss
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Gneiss is a common distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks. The foliations are characterized by alternating darker and lighter colored bands, the word gneiss comes from the Middle High German verb gneist. It has occurred in English since at least 1757, gneissic rocks are usually medium- to coarse-foliated, they are largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, gneiss rocks may also be named after a characteristic component such as garnet gneiss, biotite gneiss, albite gneiss, etc. Orthogneiss designates a gneiss derived from a rock, and paragneiss is one from a sedimentary rock. Gneissose rocks have properties similar to gneiss, gneiss appears to be striped in bands, called gneissic banding. The banding is developed under high temperature and pressure conditions, the minerals are arranged into layers that appear as bands in cross section. The appearance of layers, called compositional banding, occurs because the layers, the darker bands have relatively more mafic minerals. The lighter bands contain relatively more felsic and these forces stretch out the rock like a plastic, and the original material is spread out into sheets. Another cause of banding is metamorphic differentiation, which separates different materials into different layers through chemical reactions, not all gneiss rocks have detectable banding. In kyanite gneiss, crystals of kyanite appear as random clumps in what is mainly a plagioclase matrix, henderson gneiss is found in North Carolina and South Carolina, US, east of the Brevard Shear Zone. It has deformed into two sequential forms, the second, more warped, form is associated with the Brevard Fault, and the first deformation results from displacement to the southwest. Most of the Outer Hebrides of Scotland have a formed from Lewisian gneiss. In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree. These rocks are igneous in origin, mixed with metamorphosed marble, quartzite and mica schist with later intrusions of basaltic dikes. Gneisses of Archean and Proterozoic age occur in the Baltic Shield, in antiquity, gneisses were also utilized in architectural construction. They were used to erect the Sphinx of Taharqo in the Nile Valley, list of rock types Blatt, Harvey and Robert J. Tracy. Petrology, Igneous, Sedimentary and Metamorphic, 2nd ed. Freeman, mcKirdy, Alan, Roger Crofts and John Gordon
26.
Greenstone belt
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The name comes from the green hue imparted by the colour of the metamorphic minerals within the mafic rocks, the typical green minerals are chlorite, actinolite, and other green amphiboles. As such, understanding the nature and origin of greenstone belts is the most fruitful way of studying Archaean geological history, Greenstone belts have been interpreted as having formed at ancient oceanic spreading centers and island arc terranes. Greenstone belts are formed of volcanic rocks, dominated by basalt. Through time, the degree of sediment contained within greenstone belts has risen, and this change in nature is interpreted as a response to the maturity of the plate tectonics processes throughout the Earths geological history. Archaean plate tectonics did not take place on mature crust and as such the presence of thrust-in allochthonous greenstone belts is expected, by the Proterozoic, magmatism was occurring around cratons and with established sedimentary sources, with little recycling of the crust, allowing preservation of more sediments. By the Phanerozoic, extensive continental cover and lower heat flow from the mantle has seen greater preservation of sediments and greater influence of continental masses. Archaean greenstones are found in the Slave craton, northern Canada, Pilbara craton and Yilgarn Craton, Western Australia, Gawler Craton in South Australia, and in the Wyoming Craton in the US. Examples are found in South and Eastern Africa, namely the Kaapvaal craton and also in the core of Madagascar, as well as West Africa and Brazil, northern Scandinavia. The Abitibi greenstone belt in Ontario and Quebec is one of the largest Archean greenstone belts in the world, the belts often contain ore deposits of gold, silver, copper, zinc and lead. One of the best known greenstone belts in the world is the South African Barberton greenstone belt, the Barberton Greenstone belt was first uniquely identified by Prof Annhauser at the University of the Witwatersrand, Johannesburg. His work in mapping and detailing the characteristics of the Barberton Greenstone belt has been used as a primer for other greenstone belts around the world. He noted the existence of pillow lavas, indicating a lava being rapidly cooled in water, as well as the spinifex textures created by crystals formed under rapidly cooling environments, accretionary history of the Archean Barberton Greenstone Belt, southern Africa
27.
Precambrian
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The Precambrian is the earliest period of Earths history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons of the time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 541 million years ago, the Precambrian accounts for 89% of geologic time. Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earths history, the Precambrian fossil record is poorer than that of the succeeding Phanerozoic, and fossils from that time are of limited biostratigraphic use. This is because many Precambrian rocks have been metamorphosed, obscuring their origins, while others have been destroyed by erosion. A stable crust was apparently in place by 4,412 Ma, the term Precambrian is recognized by the International Commission on Stratigraphy as a general term including the Archean and Proterozoic eons. It is still used by geologists and paleontologists for general discussions not requiring the more specific eon names and it was briefly called the Cryptozoic eon. A specific date for the origin of life has not been determined, carbon found in 3.8 billion year old rocks from islands off western Greenland may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have found in Western Australia. Probable fossils 100 million years older have been found in the same area, there is a fairly solid record of bacterial life throughout the remainder of the Precambrian. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, a very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran or Vendian biota, hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic era. By the middle of the following Cambrian period, a diverse fauna is recorded in the Burgess Shale. The explosion in diversity of lifeforms during the early Cambrian is called the Cambrian explosion of life, while land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas. Evidence of the details of plate motions and other activity in the Precambrian has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, the supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, one of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a Snowball Earth. The atmosphere of the early Earth is not well understood, most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen
28.
Quartzite
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Quartzite is a hard, non-foliated metamorphic rock which was originally pure quartz sandstone. Sandstone is converted into quartzite through heating and pressure related to tectonic compression within orogenic belts. Pure quartzite is usually white to grey, though quartzites often occur in shades of pink. Other colors, such as yellow, green, blue 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 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, carbonate and clay, often migrate during recrystallization and metamorphosis. This causes streaks and lenses to form within the quartzite, orthoquartzite is a very pure quartz sandstone composed of usually well-rounded quartz grains cemented by silica. Orthoquartzite is often 99% SiO2 with only minor amounts of iron oxide and trace resistant minerals such as zircon, rutile. Although few fossils are present, the original texture and sedimentary structures are preserved. The term is traditionally used for quartz-cemented quartz arenites. Quartzite is very resistant to weathering and often forms ridges. The nearly pure silica content of the rock provides little for soil, therefore, because of its hardness and angular shape, crushed quartzite is often used as railway ballast. Quartzite is a stone and may be used to cover walls, as roofing tiles, as flooring. Its use for countertops in kitchens is expanding rapidly and it is harder and more resistant to stains than granite. Crushed quartzite is used in road construction. High purity quartzite is used to produce ferrosilicon, industrial silica sand, during the Paleolithic quartzite was used, in addition to flint, quartz, and other lithic raw materials, for making stone tools. Quartzite is also 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
29.
Mudrock
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Mudrocks are a class of fine grained siliciclastic sedimentary rocks. The varying types of mudrocks include, siltstone, claystone, mudstone, slate, most of the particles of which the stone is composed are less than 0.0625 mm and are too small to study readily in the field. At first sight the rock types look quite similar, however, there are important differences in composition, there has been a great deal of disagreement involving the classification of mudrocks. Fine sediment is the most abundant product of erosion, and these contribute to the overall omnipresence of mudrocks. With increased pressure over time the platey clay minerals may become aligned and this finely bedded material that splits readily into thin layers is called shale, as distinct from mudstone. The lack of fissility or layering in mudstone may be due either to the texture or to the disruption of layering by burrowing organisms in the sediment prior to lithification. From the beginning of civilization, when pottery and mudbricks were made by hand, to now, literature on this omnipresent rock-type has been increasing in recent years, and technology continues to allow for better analysis. Mudrocks, by definition, consist of at least fifty percent mud-sized particles, specifically, mud is composed of silt-sized particles that are between 1/16 – 1/256 of a millimeter in diameter, and clay-sized particles which are less than 1/256 millimeter. Mudrocks contain mostly clay minerals, and quartz and feldspars and they can also contain the following particles at less than 63 micrometres, calcite, dolomite, siderite, pyrite, marcasite, heavy minerals, and even organic carbon. There are various synonyms for fine-grained siliciclastic rocks containing fifty percent or more of its constituents less than 1/256 of a millimeter. Mudstones, shales, lutites, and argillites are common qualifiers, or umbrella-terms, however, the term mudrock allows for further subdivisions of siltstone, claystone, mudstone, and shale. For example, a siltstone would be made of more than 50-percent grains that equate to 1/16 - 1/256 of a millimeter, Shale denotes fissility, which implies an ability to part easily or break parallel to stratification. Siltstone, mudstone, and claystone implies lithified, or hardened, a claystone is lithified, and non-fissile mudrock. In order for a rock to be considered a claystone, it must consist of up to fifty percent clay, clay minerals are integral to mudrocks, and represent the first or second most abundant constituent by volume. There are 35 recognized clay mineral species on Earth and they make muds cohesive and plastic, or able to flow. Clay is by far the smallest particles recognized in mudrocks, most materials in nature are clay minerals, but quartz, feldspar, iron oxides, and carbonates can weather to sizes of a typical clay mineral. For a size comparison, a particle is 1/1000 the size of a sand grain. This means a particle will travel 1000 times further at constant water velocity
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Lake Missoula
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Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago. The lake measured about 7,770 square kilometres and contained about 2,100 cubic kilometres of water, the lake was the result of an ice dam on the Clark Fork caused by the southern encroachment of a finger of the Cordilleran Ice Sheet into the Idaho Panhandle. The height of the ice dam typically approached 610 metres, flooding the valleys of western Montana approximately 320 kilometres eastward and it was the largest ice-dammed lake known to have occurred. The cumulative effect of the floods was to excavate 210 cubic kilometres of loess, sediment and basalt from the scablands of eastern Washington. These floods are noteworthy for producing canyons and other geologic features through cataclysms rather than through more typical gradual processes. Based upon these criteria, Quaternary geologists estimated that the oldest of the Pleistocene Missoula floods happened before 1.5 million years ago, the older Pleistocene glaciofluvial deposits within the Hanford formation are fragmentary in nature because they have been repeatedly eroded and largely removed by subsequent Missoula floods
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Montana
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Montana /mɒnˈtænə/ is a state in the Western region of the United States. The states name is derived from the Spanish word montaña, Montana has several nicknames, although none official, including Big Sky Country and The Treasure State, and slogans that include Land of the Shining Mountains and more recently The Last Best Place. Montana has a 545-mile border with three Canadian provinces, British Columbia, Alberta, and Saskatchewan, the state to do so. It also borders North Dakota and South Dakota to the east, Wyoming to the south, Montana is ranked 4th in size, but 44th in population and 48th in population density of the 50 United States. The western third of Montana contains numerous mountain ranges, smaller island ranges are found throughout the state. In total,77 named ranges are part of the Rocky Mountains, the eastern half of Montana is characterized by western prairie terrain and badlands. The economy is based on agriculture, including ranching and cereal grain farming. Other significant economic activities include oil, gas, coal and hard rock mining, lumber, the health care, service, and government sectors also are significant to the states economy. Millions of tourists annually visit Glacier National Park, the Little Bighorn Battlefield National Monument, the name Montana comes from the Spanish word Montaña and the Latin word Montana, meaning mountain, or more broadly, mountainous country. Montaña del Norte was the name given by early Spanish explorers to the mountainous region of the west. The name was changed by Representatives Henry Wilson and Benjamin F. Harding, when Ashley presented a bill to establish a temporary government in 1864 for a new territory to be carved out of Idaho, he again chose Montana Territory. This time Rep. Samuel Cox, also of Ohio, objected to the name, Cox complained that the name was a misnomer given most of the territory was not mountainous and that a Native American name would be more appropriate than a Spanish one. Other names such as Shoshone were suggested, but it was decided that the Committee on Territories could name it whatever they wanted, with an area of 147,040 square miles, Montana is slightly larger than Japan. It is the fourth largest state in the United States after Alaska, Texas, and California, the largest landlocked U. S. state, and the worlds 56th largest national state/province subdivision. To the north, Montana shares a 545-mile border with three Canadian provinces, British Columbia, Alberta, and Saskatchewan, the state to do so. It borders North Dakota and South Dakota to the east, Wyoming to the south, the states topography is roughly defined by the Continental Divide, which splits much of the state into distinct eastern and western regions. Most of Montanas 100 or more named mountain ranges are in the western half. The Absaroka and Beartooth ranges in the states south-central part are part of the Central Rocky Mountains
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Intrusive rock
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Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, batholiths, dikes, sills, laccoliths, and volcanic necks. Intrusive rock forms within Earths crust from the crystallization of magma, magma slowly pushes up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the magma slowly cools into a solid, the different parts of the magma crystallize into rocks, many mountain ranges, such as the Sierra Nevada in California, are formed mostly from large granite intrusions, see Sierra Nevada Batholith. Intrusions are one of the two ways igneous rock can form, the other is extrusive rock, that is, an eruption or similar event. Technically speaking, an intrusion is any formation of igneous rock, rock formed from magma that cools. In contrast, an extrusion consists of rock, rock formed above the surface of the crust. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons, plutonic rocks form 7% of the Earths current land surface. Coarse-grained intrusive igneous rocks form at depth within the earth are called abyssal while those that form near the surface are called subvolcanic or hypabyssal. The term intrusive suite seems near synonymous, there is, however, a modest difference, An intrusive suite is a group of plutons related in time and space. Intrusions vary widely, from mountain-range-sized batholiths to thin veinlike fracture fillings of aplite or pegmatite, when exposed by erosion, such batholiths may occupy large areas. A well-known example of an intrusion is Devils Tower, another is Shiprock, New Mexico, USA. Be the pluton is large, it may be called a batholith or a stock, Intrusive rocks are characterized by large crystal sizes, and as the individual crystals are visible, the rock is called phaneritic. This is as the magma cools underground, and while cooling may be fast or slow, cooling is slower than on the surface, if it runs parallel to rock layers, it is called a sill. If an intrusion makes rocks above rise to form a dome, as heat dissipation is slow, and as the rock is under pressure, crystals form, and no vitreous rapidly chilled matter is present. The intrusions did not flow while solidifying, hence do not show lines, contained gases could not escape through the thick strata, thus form cavities, which can often be observed. Because their crystals are of the rough equal size, these rocks are said to be equigranular, there is typically no distinction between a first generation of large well-shaped crystals and a fine-grained ground-mass. Earlier crystals originated at a time when most of the rock was still liquid and are more or less perfect, later crystals are less regular in shape because they were compelled to occupy the spaces left between the already-formed crystals. The former case is said to be idiomorphic, the latter is xenomorphic, there are also many other characteristics that serve to distinguish the members of these two groups
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Volcanic rock
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Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin, for these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term volcanic is often applied to what are strictly metavolcanic rocks, Volcanic rocks are among the most common rock types on Earths surface, particularly in the oceans. On land, they are common at plate boundaries and in flood basalt provinces. It has been estimated that volcanic rocks cover about 8% of the Earths current land surface, lava Tephra Volcanic bomb Lapilli Volcanic ash Volcanic rocks are usually fine-grained or aphanitic to glass in texture. They often contain clasts of other rocks and phenocrysts, phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava, pumice is a highly vesicular rock produced in explosive volcanic eruptions. Most modern petrologists classify igneous rocks, including rocks, by their chemistry when dealing with their origin. The fact that different mineralogies and textures may be developed from the same initial magmas has led petrologists to rely heavily on chemistry to look at a volcanic rocks origin. The chemistry of volcanic rocks is dependent on two things, the composition of the primary magma and the subsequent differentiation. Differentiation of most volcanic rocks tends to increase the silica content, the initial composition of most volcanic rocks is basaltic, albeit small differences in initial compositions may result in multiple differentiation series. The most common of these series are tholeiitic, calc-alkaline, most volcanic rocks share a number of common minerals. Differentiation of volcanic rocks tends to increase the silica content mainly by fractional crystallization, thus, more evolved volcanic rocks tend to be richer in minerals with a higher amount if silica such as phyllo and tectosilicates including the feldspars, quartz polymorphs and muscovite. While still dominated by silicates, more volcanic rocks have mineral assemblages with less silica, such as olivine. Bowens reaction series correctly predicts the order of formation of the most common minerals in volcanic rocks, occasionally, a magma may pick up crystals that crystallized from another magma, these crystals are called xenocrysts. Diamonds found in kimberlites are rare but well-known xenocrysts, the kimberlites do not create the diamonds, Volcanic rocks are named according to both their chemical composition and texture. Basalt is a common volcanic rock with low silica content
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Clastic rock
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Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering. Geologists use the term clastic with reference to sedimentary rocks as well as to particles in sediment transport whether in suspension or as bed load, clastic sedimentary rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. Clastic sediments or sedimentary rocks are classified based on size, clast and cementing material composition. The classification factors are often useful in determining a samples environment of deposition, an example clastic environment would be a river system in which the full range of grains being transported by the moving water consist of pieces eroded from solid rock upstream. Grain size varies from clay in shales and claystones, through silt in siltstones, sand in sandstones, the Krumbein phi scale numerically orders these terms in a logarithmic size scale. Siliciclastic rocks are clastic rocks that are composed almost exclusively of silicon. The composition of sedimentary rocks includes the chemical and mineralogical components of the framework as well as the cementing material that make up these rocks. Boggs divides them into four categories, major minerals, accessory minerals, rock fragments, major minerals can be categorized into subdivisions based on their resistance to chemical decomposition. Those that possess a great resistance to decomposition are categorized as stable, while those that do not are considered less stable, the most common stable mineral in siliciclastic sedimentary rocks is quartz. Quartz makes up approximately 65 percent of framework grains present in sandstones, less stable minerals present in this type of rocks are feldspars, including both potassium and plagioclase feldspars. Feldspars comprise a considerably lesser portion of framework grains and minerals and they only make up about 15 percent of framework grains in sandstones and 5% of minerals in shales. Clay mineral groups are present in mudrocks but can be found in other siliciclastic sedimentary rocks at considerably lower levels. Accessory minerals are associated with those whose presence in the rock are not directly important to the classification of the specimen and these generally occur in smaller amounts in comparison to the quartz, and feldspars. Furthermore, those that do occur are generally heavy minerals or coarse grained micas, rock fragments also occur in the composition of siliciclastic sedimentary rocks and are responsible for about 10 -15 percent of the composition of sandstone. They generally make up most of the gravel size particles in conglomerates, though they sometimes are, rock fragments are not always sedimentary in origin. They can also be metamorphic or igneous, chemical cements vary in abundance but are predominantly found in sandstones. The two major types, are based and carbonate based
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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
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Grain size
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Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials and this is different from the crystallite size, which refers to the size of a single crystal inside a particle or grain. A single grain can be composed of several crystals, granular material can range from very small colloidal particles, through clay, silt, sand, gravel, and cobbles, to boulders. Size ranges define limits of classes that are given names in the Wentworth scale used in the United States, the Krumbein phi scale, a modification of the Wentworth scale created by W. C. This equation can be rearranged to find diameter using φ, D = D0 ×2 − ϕ In some schemes, ISO 14688-1 is applicable to natural soils in situ, similar man-made materials in situ and soils redeposited by people. An accumulation of sediment can also be characterized by the size distribution. A sediment deposit can undergo sorting when a particle size range is removed by an agency such as a river or the wind, a Scale of Grade and Class Terms for Clastic Sediments
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Conglomerate (geology)
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Conglomerates form by the consolidation and lithification of gravel. The size and composition of the fraction of a conglomerate may or may not vary in composition, sorting. In some conglomerates, the gravel-size class consist almost entirely of what were clay clasts at the time of deposition, conglomerates can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. A sedimentary rock composed largely of gravel is first named according to the roundness of the gravel, if the gravel clasts that comprise it is largely well-rounded to subrounded, it is a conglomerate. If the gravel clasts that comprise it are largely angular, it is a breccia, such breccias can be called sedimentary breccias to differentiate them from other types of breccia, e. g. volcanic and fault breccias. Sedimentary rocks that contain a mixture of rounded and angular gravel clasts are sometimes called breccio-conglomerate, conglomerates are rarely composed entirely of gravel-size clasts. Typically, the space between the gravel-size clasts is filled by a mixture composed of varying amounts of silt, sand, paraconglomerates are also often unstratified and can contain more matrix than gravel clasts. If the gravel clasts of a conglomerate are in contact with each other, unlike paraconglomerates, orthoconglomerates are typically cross-bedded and often well-cemented and lithified by either calcite, hematite, quartz, or clay. The differences between paraconglomerates and orthoconglomerates reflect differences in how they are deposited, paraconglomerates are commonly either glacial tills or debris flow deposits. Orthoconglomerates are typically associated with aqueous currents, conglomerates are also classified according to the composition of their clasts. A conglomerate or any clastic sedimentary rock that consists of a rock or mineral is known as either a monomict, monomictic, oligomict. If the conglomerate consists of two or more different types of rocks, minerals, or combination of both, it is known as either a polymict or polymictic conglomerate. If a polymictic conglomerate contains an assortment of the clasts of metastable and unstable rocks and minerals, two recognized types of type of intraformational conglomerates are shale-pebble and flat-pebble conglomerates. Finally, conglomerates are often differentiated and named according to the dominant clast size comprising them, conglomerates are deposited in a variety of sedimentary environments. In turbidites, the part of a bed is typically coarse-grained. In this setting, conglomerates are normally very well sorted, well-rounded, conglomerates are normally present at the base of sequences laid down during marine transgressions above an unconformity, and are known as basal conglomerates. They represent the position of the shoreline at a time and are diachronous. Conglomerates deposited in environments are typically well rounded and well sorted
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Sandstone
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Sandstone is a clastic sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz or feldspar because these are the most common minerals in the Earths crust, like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, quartz-bearing sandstone is converted into quartzite through heating and pressure, usually related to tectonic compression within orogenic belts. They are formed from cemented grains that may either be fragments of a rock or be mono-minerallic crystals. The cements binding these grains together are typically calcite, clays, grain sizes in sands are defined within the range of 0.0625 mm to 2 mm. The formation of sandstone involves two principal stages, first, a layer or layers of sand accumulates as the result of sedimentation, either from water or from air. Typically, sedimentation occurs by the settling out from suspension. The most common cementing materials are silica and calcium carbonate, which are derived either from dissolution or from alteration of the sand after it was buried. Colours will usually be tan or yellow, a predominant additional colourant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red, with additional manganese imparting a purplish hue. Red sandstones are seen in the Southwest and West of Britain, as well as central Europe. The regularity of the latter favours use as a source for masonry, either as a building material or as a facing stone. These physical properties allow the grains to survive multiple recycling events. Quartz grains evolve from rock, which are felsic in origin. Feldspathic framework grains are commonly the second most abundant mineral in sandstones, Feldspar can be divided into two smaller subdivisions, alkali feldspars and plagioclase feldspars. The different types of feldspar can be distinguished under a petrographic microscope, below is a description of the different types of feldspar. Alkali feldspar is a group of minerals in which the composition of the mineral can range from KAlSi3O8 to NaAlSi3O8. Plagioclase feldspar is a group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8. Lithic framework grains are pieces of ancient source rock that have yet to weather away to individual mineral grains, accessory minerals are all other mineral grains in a sandstone, commonly these minerals make up just a small percentage of the grains in a sandstone
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Mudstone
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Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope, with increased pressure over time, the platey clay minerals may become aligned, with the appearance of fissility or parallel layering. This finely bedded material that splits readily into thin layers is called shale, the lack of fissility or layering in mudstone may be due to either original texture or the disruption of layering by burrowing organisms in the sediment prior to lithification. Mud rocks such as mudstone and shale comprise some 65% of all sedimentary rocks, mudstone looks like hardened clay and, depending upon the circumstances under which it was formed, it may show cracks or fissures, like a sun-baked clay deposit. Mudstone can be separated into categories, Siltstone – more than half of the composition is silt-sized particles. Claystone – more than half of the composition is clay-sized particles, mudstone – hardened mud, a mix of silt and clay sized particles. Mudstone can include, Shale – exhibits lamination or fissility, argillite – has undergone low-grade metamorphism. In the Dunham classification of limestones, a mudstone is a carbonate rock that contains less than 10% allochems in a carbonate mud matrix. As defined by the Dunham classification, a mudstone is more or less synonymous with calcilutite, on December 13,2016, NASA reported further evidence supporting habitability on the planet Mars as the Curiosity rover climbed higher, studying younger layers, on Mount Sharp. Also reported, the soluble element boron was detected for the first time on Mars. Since landing on Mars in August 2012, Curiosity has driven 15.0 km, mudstone on planet Mars Aeolis quadrangle Composition of Mars Timeline of Mars Science Laboratory Tonstein
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Mantle (geology)
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
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Xenolith
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A xenolith is a rock fragment which becomes enveloped in a larger rock during the latters development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement, a xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes, although the term xenolith is most commonly associated with igneous inclusions, a broad definition could include rock fragments which have become encased in sedimentary rock. Xenoliths are sometimes found in recovered meteorites, xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the mantle, often contain fragments. Xenoliths of dunite, peridotite and spinel lherzolite in basaltic lava flows are one example, kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition. The aluminium-bearing minerals of these fragments provide clues to the depth of origin, calcic plagioclase is stable to a depth of 25 km. Between 25 km and about 60 km, spinel is the stable aluminium phase, at depths greater than about 60 km, dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain xenoliths of eclogite, which is considered to be the high-pressure metamorphic product of basaltic oceanic crust, the large-scale inclusion of foreign rock strata at the margins of an igneous intrusion is called a roof pendant. Blatt, Harvey, and Robert J. Tracy
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Olivine
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The mineral olivine is a magnesium iron silicate with the formula 2SiO4. Thus it is a type of nesosilicate or orthosilicate and it is a common mineral in the Earths subsurface but weathers quickly on the surface. The ratio of magnesium and iron varies between the two endmembers of the solid solution series, forsterite and fayalite, compositions of olivine are commonly expressed as molar percentages of forsterite and fayalite. Forsterite has a high melting temperature at atmospheric pressure, almost 1,900 °C. The melting temperature varies smoothly between the two endmembers, as do other properties, olivine incorporates only minor amounts of elements other than oxygen, silicon, magnesium and iron. Manganese and nickel commonly are the elements present in highest concentrations. Olivine gives its name to the group of minerals with a structure which includes tephroite, monticellite and kirschsteinite. It has a structure similar to magnetite but uses one quadravalent. Olivine gemstones are called peridot and chrysolite, olivine is named for its typically olive-green color, though it may alter to a reddish color from the oxidation of iron. Translucent olivine is sometimes used as a gemstone called peridot, some of the finest gem-quality olivine has been obtained from a body of mantle rocks on Zabargad island in the Red Sea. Olivine occurs in mafic and ultramafic igneous rocks and as a primary mineral in certain metamorphic rocks. Mg-rich olivine crystallizes from magma that is rich in magnesium and low in silica and that magma crystallizes to mafic rocks such as gabbro and basalt. Ultramafic rocks such as peridotite and dunite can be left after extraction of magmas. Olivine and high pressure structural variants constitute over 50% of the Earths upper mantle, the metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite. In contrast, Mg-rich olivine does not occur stably with silica minerals, Mg-rich olivine is stable to pressures equivalent to a depth of about 410 km within Earth. Mg-rich olivine has also discovered in meteorites, on the Moon and Mars, falling into infant stars. Such meteorites include chondrites, collections of debris from the early Solar System, the spectral signature of olivine has been seen in the dust disks around young stars. The tails of comets often have the signature of olivine
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Pyroxene
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The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes are silicon-aluminum oxides with Ca, Na, Fe, Mg, Zn, Mn, Li substituting for Si, although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a structure consisting of single chains of silica tetrahedra. The name pyroxene is derived from the Ancient Greek words for fire, however, they are simply early-forming minerals that crystallized before the lava erupted. The upper mantle of Earth is composed mainly of olivine and pyroxene, a piece of the mantle is shown at right and is dominated by olivine, typical for common peridotite. Pyroxene and feldspar are the minerals in basalt and gabbro. Pyroxene minerals are named according to the chemical species occupying the X site, the Y site, cations in Y site are closely bound to 6 oxygens in octahedral coordination. Cations in the X site can be coordinated with 6 to 8 oxygen atoms, twenty mineral names are recognised by the International Mineralogical Associations Commission on New Minerals and Mineral Names and 105 previously used names have been discarded. A typical pyroxene has mostly silicon in the site and predominately ions with a charge of +2 in both the X and Y sites, giving the approximate formula XYT2O6. The names of the common calcium – iron – magnesium pyroxenes are defined in the pyroxene quadrilateral shown in Figure 2, the enstatite-ferrosilite series contain up to 5 mol. % calcium and exists in three polymorphs, orthorhombic orthoenstatite and protoenstatite and monoclinic clinoenstatite. Increasing the calcium content prevents the formation of the orthorhombic phases, there is not complete solid solution in calcium content and Mg-Fe-Ca pyroxenes with calcium contents between about 15 and 25 mol. % are not stable with respect to a pair of exolved crystals. This leads to a miscibility gap between pigeonite and augite compositions, there is an arbitrary separation between augite and the diopside-hedenbergite solid solution. The divide is taken at >45 mol. % Ca, as the calcium ion cannot occupy the Y site, pyroxenes with more than 50 mol. % calcium are not possible. A related mineral wollastonite has the formula of the hypothetical calcium end member, magnesium, calcium and iron are by no means the only cations that can occupy the X and Y sites in the pyroxene structure. A second important series of minerals are the sodium-rich pyroxenes. The inclusion of sodium, which has a charge of +1, in jadeite and aegirine this is added by the inclusion of a +3 cation on the Y site. Table 1 shows the range of other cations that can be accommodated in the pyroxene structure. For example, Na and Al give the jadeite composition, coupled substitution of a 1+ ion on the X site and a mixture of equal numbers of 2+ and 4+ ions on the Y site
44.
Iddingsite
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Iddingsite is a microcrystalline rock that is derived from alteration of olivine. It is usually studied as a mineral, and consists of a mixture of remnant olivine, clay minerals, debates over iddingsites non-definite crystal structure caused it to be de-listed as an official mineral by the IMA, thus it is properly referred to as a rock. Because iddingsite is constantly transforming it does not have a structure or a definite chemical composition. The chemical formula for iddingsite has been approximated as MgO * Fe2O3 *4 H2O where MgO can be substituted by CaO, the geologic occurrence of iddingsite is limited to extrusive or subvolcanic rocks that are formed by injection of magma near the surface. It is absent from deep-seated rocks and is found on meteorites, as it has been found on Martian meteorites, its ages have been calculated to obtain absolute ages when liquid water was at or near the surface of Mars. Iddingsite is a pseudomorph, and during the process the olivine crystals had their internal structure or chemical composition changed. This is not true for all phases of the alteration of olivine because the arrangement becomes distorted. Iddingsite has a composition that is transforming from the original olivine passing though many stages of structural and chemical change. Iddingsite has been a subject researched in recent years because of its presence in the Martian meteorites, the formation of iddingsite requires liquid water, giving scientists an estimate as to when there has been liquid water on Mars. Potassium-argon dating of the samples showed that Mars had water on its surface anywhere from 1300 Ma to 650 Ma ago. Iddingsite is a mineral that lacks a definite composition, so exact compositions cannot be calculated. An approximated composition for an end product of iddingsite has been calculated as being SiO2 = 16%, Al2O3 = 8%, Fe2O3 = 62%. Throughout the alteration process of olivine, there is a decrease in SiO2, FeO and MgO, the chemical process associated with the alteration consists of the addition of Fe2O3 and the removal of MgO. The chemical formula for iddingsite is approximated as MgO * Fe2O3 *4 H2O where MgO can be substituted by CaO by a ratio of 1,4, there are also some trace constituents of Na2O and K2O that enter iddingsite as the alteration process progresses. The geologic occurrence of Iddingsite is limited to extrusive or hypabyssal rocks, Iddingsite is an epimagmatic mineral derived during the final cooling of lava in which it occurs from a reaction between gases, water and olivine. The formation of iddingsite is not dependent on the composition of the olivine. It is however dependent on conditions, hydration and the magma from which iddingsite forms must be rich in water vapor. The alteration of olivine to iddingsite occurs in an oxidizing environment under low pressure
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Scoria
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Scoria is a highly vesicular, dark colored volcanic rock that may or may not contain crystals. It is typically dark in color, and basaltic or andesitic in composition, Scoria is relatively low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water. Scoria may form as part of a flow, typically near its surface, or as fragmental ejecta. Most scoria is composed of fragments, and may contain phenocrysts. The word scoria comes from the Greek σκωρία, skōria, rust, an old name for scoria is cinder. Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, the difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting. As rising magma encounters lower pressures, dissolved gases are able to exsolve, some of the vesicles are trapped when the magma chills and solidifies. Vesicles are usually small, spheroidal and do not impinge upon one another, volcanic cones of scoria can be left behind after eruptions, usually forming mountains with a crater at the summit. An example is Maungarei in New Zealand, which like Te Tatua-a-Riukiuta in the south of the city has been extensively quarried. Quincan, a form of Scoria, is quarried at Mount Quincan in Far North Queensland. Scoria has several characteristics that influence how it is used. It is somewhat porous, has high surface area and strength for its weight, Scoria is often used in landscaping and drainage works. It is also used in gas barbecue grills. Scoria can be used for high-temperature insulation, Scoria is used on oil well sites to limit mud issues with heavy truck traffic. It is also used as a traction aid on ice- and snow-covered roads, cinder Tuff Pumice Volcanoes List of rock types Rock
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Carbonate
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In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−3. The name may mean an ester of carbonic acid, an organic compound containing the carbonate group C2. In geology and mineralogy, the term carbonate can refer both to carbonate minerals and carbonate rock, and both are dominated by the ion, CO2−3. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock, sodium carbonate and potassium carbonate have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e. g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, the carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a planar arrangement, with D3h molecular symmetry. It has a mass of 60.01 g/mol and carries a total formal charge of −2. It is the base of the hydrogen carbonate ion, HCO−3. The Lewis structure of the ion has two single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen. This structure is incompatible with the symmetry of the ion. This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates. In aqueous solution, carbonate, bicarbonate, carbon dioxide, in strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2, is the main form, thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid. Carbonated water is formed by dissolving CO2 in water under pressure, in living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid. Although the carbonate salts of most metals are insoluble in water, in solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes consonant to changing temperature and pressure conditions. In the case of ions with insoluble carbonates, e. g. CaCO3. This is an explanation for the buildup of scale inside pipes caused by hard water, in organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of which is double bonded. These compounds are known as organocarbonates or carbonate esters, and have the general formula ROCOOR′
