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
Metamorphism is the change of minerals or geologic texture in pre-existing rocks, without the protolith melting into liquid magma. The change occurs primarily due to heat and the introduction of chemically active fluids, the chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earths surface due to weathering and/or diagenesis are not classified as metamorphism, Metamorphism typically occurs between diagenesis, and melting. Three types of metamorphism exist, contact and regional, Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism, Metamorphic rocks can change without melting. When pressure is applied, somewhat flattened grains that orient in the same direction have a stable configuration. The upper boundary of metamorphic conditions is related to the onset of melting processes in the rock, the maximum temperature for metamorphism is typically 700 –900 °C, depending on the pressure and on the composition of the rock.
Migmatites are rocks formed at this limit, which contain pods. Since the 1980s it has recognized that rocks are rarely dry enough. Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event, the collision of two continental plates or island arcs with continental plates produce the extreme compressional forces required for the metamorphic changes typical of regional metamorphism. These orogenic mountains are eroded, exposing the intensely deformed rocks typical of their cores. The conditions within the slab as it plunges toward the mantle in a subduction zone produce regional metamorphic effects. The techniques of structural geology are used to unravel the collisional history, regional metamorphism can be described and classified into metamorphic facies or metamorphic zones of temperature/pressure conditions throughout the orogenic terrane. Contact metamorphism occurs typically around intrusive igneous rocks as a result of the increase caused by the intrusion of magma into cooler country rock.
The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole, contact metamorphic rocks are usually known as hornfels. Rocks formed by contact metamorphism may not present signs of deformation and are often fine-grained. Contact metamorphism is greater adjacent to the intrusion and dissipates with distance from the contact, the size of the aureole depends on the heat of the intrusion, its size, and the temperature difference with the wall rocks. Dikes generally have small aureoles with minimal metamorphism whereas large ultramafic intrusions can have significantly thick, the metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. A typical geotechnical engineering project begins with a review of project needs to define the material properties. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place, a geotechnical engineer determines and designs the type of foundations, and/or pavement subgrades required for the intended man-made structures to be built. Foundations built for above-ground structures include shallow and deep foundations, retaining structures include earth-filled dams and retaining walls. Earthworks include embankments, tunnels and levees, reservoirs, deposition of hazardous waste, Geotechnical engineering is related to coastal and ocean engineering. Coastal engineering can involve the design and construction of wharves, ocean engineering can involve foundation and anchor systems for offshore structures such as oil platforms.
The fields of engineering and engineering geology are closely related. However, the field of engineering is a specialty of engineering. Humans have historically used soil as a material for flood control, irrigation purposes, burial sites, building foundations, as the cities expanded, structures were erected supported by formalized foundations, Ancient Greeks notably constructed pad footings and strip-and-raft foundations. Until the 18th century, however, no basis for soil design had been developed. Several foundation-related engineering problems, such as the Leaning Tower of Pisa, the earliest advances occurred in the development of earth pressure theories for the construction of retaining walls. Henri Gautier, a French Royal Engineer, recognized the natural slope of different soils in 1717, a rudimentary soil classification system was developed based on a materials unit weight, which is no longer considered a good indication of soil type. The application of the principles of mechanics to soils was documented as early as 1773 when Charles Coulomb developed improved methods to determine the pressures against military ramparts.
By combining Coulombs theory with Christian Otto Mohrs 2D stress state, although it is now recognized that precise determination of cohesion is impossible because c is not a fundamental soil property, the Mohr-Coulomb theory is still used in practice today. In the 19th century Henry Darcy developed what is now known as Darcys Law describing the flow of fluids in porous media, albert Atterberg developed the clay consistency indices that are still used today for soil classification. Osborne Reynolds recognized in 1885 that shearing causes volumetric dilation of dense, modern geotechnical engineering is said to have begun in 1925 with the publication of Erdbaumechanik by Karl Terzaghi. Terzaghi developed the framework for theories of bearing capacity of foundations, in his 1948 book, Donald Taylor recognized that interlocking and dilation of densely packed particles contributed to the peak strength of a soil. Critical state soil mechanics is the basis for many contemporary advanced constitutive models describing the behavior of soil, Geotechnical centrifuge modeling is a method of testing physical scale models of geotechnical problems
A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure.
Common distinguishing characteristics include crystal structure and habit, lustre, colour, tenacity, fracture, more specific tests for describing minerals include magnetism, taste or smell and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, disilicates, inosilicates, other important mineral groups include the native elements, oxides, carbonates and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which extensively involve mineralogy.
Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, crystals are periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
An Orogeny is an event that leads to a large structural deformation of the Earths lithosphere due to the interaction between tectonic plates. Orogens or orogenic belts develop when a plate is crumpled and is pushed upwards to form mountain ranges. Orogeny is the mechanism by which mountains are built on continents. The word orogeny comes from Ancient Greek, though it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny. Formation of an orogen is accomplished in part by the processes of subduction or convergence of two or more continents. Orogeny usually produces long arcuate structures, known as orogenic belts, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with zones, which consume crust, produce volcanoes. Geologists attribute the arcuate structure to the rigidity of the descending plate and these island arcs may be added to a continent during an orogenic event.
The processes of orogeny can take tens of millions of years, rock formations that undergo orogeny are severely deformed and undergo metamorphism. Orogenic processes may push deeply buried rocks to the surface, sea-bottom and near-shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, very high mountains can result, an orogenic event may be studied, as a tectonic structural event, as a geographical event, and as a chronological event. The foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the mountain belt. The basin migrates with the front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range. The fill of many such shows an change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including magmatism, crustal melting, what exactly happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, and how these properties change during orogenesis.
In addition to orogeny, the orogen is subject to other processes, for example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana. The Caledonian Orogen resulted from events and various others that are part of its peculiar orogenic cycle
Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a mineral with a specific chemical composition, plagioclase is a continuous solid solution series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826, the series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the minerals crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or record-groove effect, plagioclase is a major constituent mineral in the Earths crust, and is consequently an important diagnostic tool in petrology for identifying the composition and evolution of igneous rocks. Plagioclase is a constituent of rock in the highlands of the Earths moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars, the extinction angle is an optical characteristic and varies with the albite fraction.
There are several named plagioclase feldspars that fall between albite and anorthite in the series, the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its pure white color. It is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes, often with rarer minerals like tourmaline. The intermediate members of the group are very similar to each other. Bytownite, named after the name for Ottawa, Canada, is a rare mineral occasionally found in more basic rocks. Labradorite is the characteristic feldspar of the basic rock types such as diorite, andesite. Labradorite frequently shows an iridescent display of colors due to light refracting within the lamellae of the crystal and it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite which is composed almost entirely of plagioclase.
A variety of known as spectrolite is found in Finland. Andesine is a mineral of rocks such as diorite which contain a moderate amount of silica. Oligoclase is common in granite, syenite and gneiss and it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, sunstone is mainly oligoclase with flakes of hematite
Mudrocks are a class of fine grained siliciclastic sedimentary rocks. The varying types of mudrocks include, claystone, 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, 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, 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 contain the following particles at less than 63 micrometres, dolomite, pyrite, 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 and argillites are common qualifiers, or umbrella-terms, the term mudrock allows for further subdivisions of siltstone, claystone 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 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, 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
Schist is a medium-grade metamorphic rock with medium to large, 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, talc, hornblende 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 common, Schists are 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 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 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, 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 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 and calc-schists, with crystalline dolomites, contain silicate minerals such as mica, diopside, scapolite 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, feldspar, zoisite
In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement as a result of rock-mass movement. Large faults within the Earths crust result from the action of tectonic forces. Energy release associated with movement on active faults is the cause of most earthquakes. A fault plane is the plane that represents the surface of a fault. A fault trace or fault line is the intersection of a plane with the ground surface. A fault trace is the line commonly plotted on maps to represent a fault. Since faults do not usually consist of a single, clean fracture, the two sides of a non-vertical fault are known as the hanging wall and footwall. By definition, the wall occurs above the fault plane. This terminology comes from mining, when working a tabular ore body, because of friction and the rigidity of rocks, they cannot glide or flow past each other easily, and occasionally all movement stops. A fault in ductile rocks can release instantaneously when the rate is too great.
The energy released by instantaneous strain-release causes earthquakes, a common phenomenon along transform boundaries, slip is defined as the relative movement of geological features present on either side of a fault plane, and is a displacement vector. A faults sense of slip is defined as the motion of the rock on each side of the fault with respect to the other side. In practice, it is only possible to find the slip direction of faults. Based on direction of slip, faults can be categorized as, strike-slip. Dip-slip, offset is predominantly vertical and/or perpendicular to the fault trace, oblique-slip, combining significant strike and dip slip. The fault surface is usually vertical and the footwall moves either left or right or laterally with very little vertical motion. Strike-slip faults with left-lateral motion are known as sinistral faults. Those with right-lateral motion are known as dextral faults
A lath or slat is a thin, narrow strip of straight-grained wood used under roof shingles or tiles, on lath and plaster walls and ceilings to hold plaster, and in lattice and trellis work. Also reed mat was historically a lath material, the word is recorded from the late 13th century and is likely derived from the Old English word *læððe, a variant of the word lætt. It was improved in 1910 by the paper wrapping the edges, gypsum lath is commonly used in place of wood since it is noncombustible, easy to use, and gives better results. The popularity of the lath and plaster method declined in the 1950s, gypsum lath is available with a foil facing which acts as a vapor barrier and heat reflector, and as a veneer base for plaster veneer. Today, wooden-slat laths are still used in building construction to form a base or groundwork for plaster but modern lath and plaster applications are mostly limited to conservation projects. Individual laths were riven and nailed in place, 2) Accordion lath are thin, sawn boards partially split with a hatchet or axe, sometimes the laths need to be held off of a solid surface so the plaster can wrap around the lath.
Single pieces of lath applied to a surface for this purpose are sometimes called counter lath, laths were used to fix reed to a timber structure before plastering. Tiles and other coverings on roofs and walls are often fastened to laths, such strips of wood are employed to form lattice-work, or are used as the bars of venetian blinds, and window shutters. Lath is used on many farms in the Connecticut Valley as a means to carry. This is achieved by using one of two methods, hooking or spearing, a spear lath is just a regular lath that is held in an upright position, the worker mounts a spear on top and spears the tobacco onto the lath. The other form of lath is called Hook Lath, which just has small hooks attached that allows a worker to hook the stems of tobacco plants onto the lath, lath cut from spruce or balsam fir trees were used for building wooden lobster traps. Counter-lath is a used in roofing and plastering for a piece of wood placed perpendicular to the lath. In roofing a counter-lath is a piece of timber parallel with.
In plastering a counter lath is placed perpendicular to the lath as a fillet to space the lath off of the surface to allow the plaster to pass through the lath and key to the lath. Metal lath dates from the late 19th century and is used today with plaster and stucco in home. In these applications the lath adds strength and rigidity in addition to providing a matrix to which the stucco can adhere and this is similar to the way rebar is used to strengthen some concrete and masonry applications. Ribbed lath and expanded metal with V-shaped ribs which give it more stiffness, self-centering lath, Self-furring lath, an expanded metal lath which is dimpled to hold itself off from a solid surface. Wire lath, a welded or woven wire lath, similar to hardware cloth, paper backed wire lath, wire lath with a building paper attached
Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture, cumulate texture is diagnostic of the conditions of formation of group of igneous rocks. Cumulate rocks are the product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, cumulates are typically found in ultramafic intrusions, in the base of large ultramafic lava tubes in komatiite and magnesium rich basalt flows and in some granitic intrusions. Cumulates are named according to their dominant mineralogy and the percentage of crystals to their groundmass, adcumulates are rocks containing ~100–93% accumulated magmatic crystals in a fine-grained groundmass. Mesocumulates are rocks with between 93 and 85% accumulated minerals in a groundmass, orthocumulates are rocks containing between 85 and 75% accumulated minerals in groundmass. Cumulate rocks are named according to the cumulate minerals in order of abundance, and cumulate type.
For example, a layer with 50% plagioclase, 40% pyroxene, 5% olivine, a rock consisting of 80% olivine, 5% magnetite and 15% groundmass is an olivine mesocumulate. Cumulate terminology is appropriate for use when describing cumulate rocks, in intrusions which have a uniform composition and minimal textural and mineralogical layering or visible crystal accumulations it is inappropriate to describe them according to this convention. Cumulate rocks, because they are fractionates of a parental magma, the chemistry of the cumulate itself can inform on the residual melt composition, but several factors need to be considered. In this example, the precipitation of anorthite removes calcium from the melt, enstatite being precipitated from the melt will remove magnesium, so the melt becomes depleted in these elements. This tends to enrich the concentration of other elements - typically sodium, titanium, the rock that is made of the accumulated minerals will not have the same composition as the magma.
In the above example, the cumulate of anorthite + enstatite is rich in calcium and magnesium, the cumulate rock is a plagioclase-pyroxene cumulate and the melt is now more felsic and aluminous in composition. In the above example, the plagioclase and pyroxene need not be pure end-member compositions, the minerals can be precipitated in any ratio within the cumulate, such cumulates can be 90% plagioclase, 10% enstatite, through to 10% plagiclase, 90% enstatite and remain a gabbro. This alters the chemistry of the cumulate, and the depletions of the residual melt, in nature, cumulates usually form from 2 mineral species, although ranges from 1 to 4 mineral species are known. Cumulate rocks which are formed from one mineral alone are often named after the mineral, a specific example is the Skaergaard intrusion in Greenland. One way to infer the composition of the magma that created the cumulate rocks is to measure groundmass chemistry, complex calculations of averaging cumulate layers must be utilised, which is a complex process.
Alternatively, the composition can be estimated by assuming certain conditions of magma chemistry
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