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 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, 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 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
Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, dikes, sills 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, 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 many other characteristics that serve to distinguish the members of these two groups
Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be white, pink, or gray in color. The word granite comes from the Latin granum, a grain, in reference to the structure of such a holocrystalline rock. By definition, granite is a rock with at least 20% quartz. The term granitic means granite-like and is applied to granite and a group of igneous rocks with similar textures and slight variations in composition. Occasionally some individual crystals are larger than the groundmass, in case the texture is known as porphyritic. A granitic rock with a texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks, petrographic examination is required for identification of specific types of granitoids. The extrusive igneous rock equivalent of granite is rhyolite, Granite is nearly always massive and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone.
The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 •1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C, it is reduced in the presence of water. Granite has poor primary permeability, but strong secondary permeability, true granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite, when a granitoid contains less than 10% orthoclase, it is called tonalite and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite, two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. A worldwide average of the composition of granite, by weight percent, based on 2485 analyses. Much of it was intruded during the Precambrian age, it is the most abundant basement rock that underlies the relatively thin veneer of the continents.
Outcrops of granite tend to form tors and rounded massifs, granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite often occurs as small, less than 100 km² stock masses
Fractional crystallization (geology)
Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within the Earths crust and mantle. It is one of the processes of magmatic differentiation. Fractional crystallization is the removal and segregation from a melt of mineral precipitates, except in special cases, in essence, fractional crystallization is the removal of early formed crystals from an originally homogeneous magma so that these crystals are prevented from further reaction with the residual melt. The composition of the melt becomes relatively depleted in some components and enriched in others. Addition and loss of water, carbon dioxide, for example, the partial pressure of water in silicate melts can be of prime importance, as in near-solidus crystallization of magmas of granite composition. Experiments have provided examples of the complexities that control which mineral is crystallized first as the melt cools down past the liquidus. One example concerns crystallization of melts that form mafic and ultramafic rocks, mgO and SiO2 concentrations in melts are among the variables that determine whether forsterite olivine or enstatite pyroxene is precipitated, but the water content and pressure are important.
In some compositions, at high pressures without water crystallization of enstatite is favored, granitic magmas provide additional examples of how melts of generally similar composition and temperature, but at different pressure, may crystallize different minerals. Pressure determines the water content of a magma of granite composition. During the process of crystallization, melts become enriched in incompatible elements. Hence, knowledge of the sequence is critical in understanding how melt compositions evolve. Textures of rocks provide insights, as documented in the early 1900s by Bowens reaction series, a variety of Cr, Fe, and Ti oxides show such textures, like intergranular chromite in a siliceous matrix. Experimentally-determined phase diagrams for simple mixtures provide insights into general principles, numerical calculations with special software have become increasingly able to simulate natural processes accurately. Cumulate rock Flow banding Fractional crystallization Igneous differentiation Layered intrusion
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. This type of volcanism falls under the umbrella of plate hypothesis volcanism, Volcanism away from plate boundaries has been explained as mantle plumes. These so-called hotspots, for example Hawaii, are postulated to arise from upwelling diapirs with magma from the boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology.
The study of volcanoes is called volcanology, sometimes spelled vulcanology, at the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Most divergent plate boundaries are at the bottom of the oceans, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.
Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
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 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 be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, laccoliths and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, 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, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, 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 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
Pumice, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker walls and being dark colored. Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano, the unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases that are dissolved in the lava, the simultaneous cooling and depressurization freezes the bubbles in a matrix. Eruptions under water are cooled and the large volume of pumice created can be a shipping hazard for cargo ships. Pumice is composed of highly microvesicular glass pyroclastic with very thin and it is commonly, but not exclusively of silicic or felsic to intermediate in composition, but basaltic and other compositions are known.
Pumice is commonly pale in color, ranging from white, blue or grey and it forms when volcanic gases exsolving from viscous magma form bubbles that remain within the viscous magma as it cools to glass. Pumice is a product of explosive eruptions and commonly forms zones in upper parts of silicic lavas. Pumice has a porosity of 90%, and initially floats on water. Scoria differs from pumice in being denser, with larger vesicles and thicker vesicle walls, it sinks rapidly. The difference is the result of the viscosity of the magma that forms scoria. When larger amounts of gas are present, the result is a variety of pumice known as pumicite. Pumice is considered a glass because it has no crystal structure, pumice varies in density according to the thickness of the solid material between the bubbles, many samples float in water. After the explosion of Krakatoa, rafts of pumice drifted through the Pacific Ocean for up to 20 years, in fact, pumice rafts disperse and support several marine species. In 1979,1984 and 2006, underwater volcanic eruptions near Tonga created large pumice rafts, there are two main forms of vesicles.
Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric, the elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high pressure during eruption. Pumice is widely used to make concrete or insulative low-density cinder blocks
Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate, between that of gabbro and felsic granite. Diorite is usually grey to dark-grey in colour, but it can be black or bluish-grey and it is distinguished from gabbro on the basis of the composition of the plagioclase species, the plagioclase in diorite is richer in sodium and poorer in calcium. Diorite may contain small amounts of quartz and olivine, apatite, magnetite and sulfides occur as accessory minerals. Minor amounts of muscovite may be present, varieties deficient in hornblende and other dark minerals are called leucodiorite. When olivine and more iron-rich augite are present, the grades into ferrodiorite. The presence of significant quartz makes the rock type quartz-diorite or tonalite, and if orthoclase is present at greater than 10 percent, a dioritic rock containing feldspathoid mineral/s and no quartz is termed foid-bearing diorite or foid diorite according to content.
Diorite has a phaneritic, often speckled, texture of coarse grain size and is occasionally porphyritic, orbicular diorite shows alternating concentric growth bands of plagioclase and amphibole surrounding a nucleus, within a diorite porphyry matrix. Diorites may be associated with granite or gabbro intrusions, into which they may subtly merge. Diorite results from the melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in mountain building, such as in the Andes Mountains. The extrusive volcanic equivalent rock type is andesite, diorite is an extremely hard rock, making it difficult to carve grand work with. It is so hard that ancient civilizations used diorite balls to work granite and its hardness, allows it to be worked finely and take a high polish, and to provide a durable finished work. One comparatively frequent use of diorite was for inscription, as it is easier to carve in relief than in three-dimensional statuary, perhaps the most famous diorite work extant is the Code of Hammurabi, inscribed upon a 2.23 m pillar of black diorite.
The original can be today in Paris Musée du Louvre. The use of diorite in art was most important among very early Middle Eastern civilizations such as Ancient Egypt, Babylonia and Sumer. It was so valued in early times that the first great Mesopotamian empire—the Empire of Sargon of Akkad—listed the taking of diorite as a purpose of military expeditions. Although one can find diorite art from periods, it more popular as a structural stone and was frequently used as pavement due to its durability
Tonalite is an igneous, plutonic rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase with 10% or less alkali feldspar, quartz is present as more than 20% of the rock. Amphiboles and pyroxenes are common accessory minerals, in older references tonalite is sometimes used as a synonym for quartz diorite. However the current IUGS classification defines tonalite as having greater than 20% quartz, the name is derived from the type locality of tonalites, adjacent to the Tonale Line, a major structural lineament and mountain pass, Tonale Pass, in the Italian and Austrian Alps. Trondhjemite is an orthoclase-deficient variety of tonalite with minor biotite as the only mafic mineral, named after Norways third largest city, media related to Tonalite at Wikimedia Commons
Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations. Some syenites contain larger proportions of mafic components and smaller amounts of material than most granites. The volcanic equivalent of syenite is trachyte, the feldspar component of syenite is predominantly alkaline in character. Plagioclase feldspars may be present in small proportions, less than 10%, such feldspars often are interleaved as perthitic components of the rock. When ferromagnesian minerals are present in syenite at all, they occur in the form of hornblende, amphibole. Biotite is rare, because in a syenite magma the formation of feldspar consumes nearly all the aluminium, syenites are products of alkaline igneous activity, generally formed in thick continental crustal areas, or in Cordilleran subduction zones. To produce a syenite, it is necessary to melt a granitic or igneous protolith to a low degree of partial melting.
At very low degrees of partial melting a silica undersaturated melt is produced, forming a nepheline syenite, conversely in certain conditions, large volumes of anorthite crystals may precipitate from thoroughly molten magma in a cumulate process as it cools. This leaves a drastically reduced concentration of silica in the remainder of the melt, the segregation of the silica from the melt leaves it in a state that may favour syenite formation. Syenite is not a common rock, regions where it occurs in significant quantities include the following. In North America syenite occurs in Arkansas and Montana, regions in New England have sizable amounts, and in New York syenite gneisses occur. The great syenite dyke extends from Hanging Rock, South Carolina through Taxahaw, South Carolina to the Brewer and Edgeworth mine in Chesterfield, in Europe syenite may be found in parts of Switzerland, Norway, Portugal, in Plovdiv, Bulgaria and in Ditrău, Romania. In Africa there are syenite formations in Aswan, syenite rock was used to make the Quay with Sphinxes.
Instead of the usual rock syenite, some of the important events in New England, Montana, New York, Germany, Plovdiv, Malawi. The Malvern Hills, which is on the border between the counties of Herefordshire and Worcestershire United Kingdom are formed of syenite and Kangerluluk fjords in southeastern Greenland, where a bay within the latter and a headland are named after the rock. The term syenite was originally applied to hornblende granite like that of Syene in Egypt, episyenite is a term used in petrology to describe the depletion of silicon dioxide in rock rich in that compound. A process that results in depletion often is termed episyenitization, the term refers only to the macroscopic effect of relative depletion in a rock, it does not imply anything about the nature of the physical processes leading to the depletion in any particular case. Many different metamorphic processes can lead to episyenitization, microscopic Petrography, McGraw-Hill,1956 list of rock types
Dr Kiyoo Mogi is a prominent seismologist. He is regarded as Japans foremost authority on earthquake prediction and is a chair of the Japanese Coordinating Committee for Earthquake Prediction. Mogi is a former Director of the University of Tokyos Earthquake Research Institute, was a professor at Nihon University and is professor emeritus at Tokyo University, due to the seismic activity in Japan, Mogi has taken an interest in safety of nuclear power in Japan. In 1969 Mogi predicted that there was a possibility of a shallow magnitude 8.0 earthquake in the Tōkai region of Japan, an area that has experienced a number of previous large earthquakes. He went on to chair the ECA from 1991 until he resigned the post in 1996 after failing to persuade the government of the need to take uncertainty into account when issuing warnings. Previously, in 2004, he had stated that the issue is a problem which can bring a catastrophe to Japan through a man-made disaster. The Mogi doughnut is one of several hypotheses that have been proposed.
In 1958 Mogi was responsible for an advance in understanding the dynamics of volcanos. The Mogi model subsequently became the first commonly used method in volcanology. Experimental Rock Mechanics Earthquake Prediction Hamaoka Nuclear Power Plant Fukushima I nuclear accidents Katsuhiko Ishibashi Nuclear power in Japan Geology of Japan Pacific Ring of Fire