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120-771: The Badenoch Group is a sequence of metamorphosed Tonian age sedimentary rocks that outcrop across the Central Highlands of Scotland , east of the Great Glen . This rock sequence has formerly been referred to as the Central Highland Migmatite Complex and the Central Highland Division. Badenoch Group rocks extend across the Monadhliath Mountains and some surrounding areas largely between

240-554: A clue as to the temperatures and pressures at the time of metamorphism. These reactions are possible because of rapid diffusion of atoms at elevated temperature. Pore fluid between mineral grains can be an important medium through which atoms are exchanged. A particularly important group of neocrystallization reactions are those that release volatiles such as water and carbon dioxide . During metamorphism of basalt to eclogite in subduction zones , hydrous minerals break down, producing copious quantities of water. The water rises into

360-416: A decarbonation reaction is: In plastic deformation pressure is applied to the protolith , which causes it to shear or bend, but not break. In order for this to happen temperatures must be high enough that brittle fractures do not occur, but not so high that diffusion of crystals takes place. As with pressure solution, the early stages of plastic deformation begin during diagenesis. Regional metamorphism

480-410: A deficit or a surplus of electrons are called ions . Electrons that are farthest from the nucleus may be transferred to other nearby atoms or shared between atoms. By this mechanism, atoms are able to bond into molecules and other types of chemical compounds like ionic and covalent network crystals . By definition, any two atoms with an identical number of protons in their nuclei belong to

600-422: A different way, is internal conversion —a process that produces high-speed electrons that are not beta rays, followed by production of high-energy photons that are not gamma rays. A few large nuclei explode into two or more charged fragments of varying masses plus several neutrons, in a decay called spontaneous nuclear fission . Each radioactive isotope has a characteristic decay time period—the half-life —that

720-456: A finite set of orbits, and could jump between these orbits only in discrete changes of energy corresponding to absorption or radiation of a photon. This quantization was used to explain why the electrons' orbits are stable and why elements absorb and emit electromagnetic radiation in discrete spectra. Bohr's model could only predict the emission spectra of hydrogen, not atoms with more than one electron. Back in 1815, William Prout observed that

840-529: A form of light but made of negatively charged particles because they can be deflected by electric and magnetic fields. He measured these particles to be at least a thousand times lighter than hydrogen (the lightest atom). He called these new particles corpuscles but they were later renamed electrons since these are the particles that carry electricity. Thomson also showed that electrons were identical to particles given off by photoelectric and radioactive materials. Thomson explained that an electric current

960-419: A fractional electric charge. Protons are composed of two up quarks (each with charge + ⁠ 2 / 3 ⁠ ) and one down quark (with a charge of − ⁠ 1 / 3 ⁠ ). Neutrons consist of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles. The quarks are held together by the strong interaction (or strong force), which

1080-484: A given accuracy in measuring a position one could only obtain a range of probable values for momentum, and vice versa. Thus, the planetary model of the atom was discarded in favor of one that described atomic orbital zones around the nucleus where a given electron is most likely to be found. This model was able to explain observations of atomic behavior that previous models could not, such as certain structural and spectral patterns of atoms larger than hydrogen. Though

1200-451: A mathematical function that characterises the probability that an electron appears to be at a particular location when its position is measured. Only a discrete (or quantized ) set of these orbitals exist around the nucleus, as other possible wave patterns rapidly decay into a more stable form. Orbitals can have one or more ring or node structures, and differ from each other in size, shape and orientation. Each atomic orbital corresponds to

1320-517: A metabasalt. When the protolith cannot be determined, the rock is classified by its mineral composition or its degree of foliation. Metamorphic grade is an informal indication of the amount or degree of metamorphism. In the Barrovian sequence (described by George Barrow in zones of progressive metamorphism in Scotland), metamorphic grades are also classified by mineral assemblage based on

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1440-411: A metamorphic event. The facies are named after the metamorphic rock formed under those facies conditions from basalt . The particular mineral assemblage is somewhat dependent on the composition of that protolith, so that (for example) the amphibolite facies of a marble will not be identical with the amphibolite facies of a pellite. However, the facies are defined such that metamorphic rock with as broad

1560-415: A particular energy level of the electron. The electron can change its state to a higher energy level by absorbing a photon with sufficient energy to boost it into the new quantum state. Likewise, through spontaneous emission , an electron in a higher energy state can drop to a lower energy state while radiating the excess energy as a photon. These characteristic energy values, defined by the differences in

1680-526: A range of compositions as is practical can be assigned to a particular facies. The present definition of metamorphic facies is largely based on the work of the Finnish geologist, Pentti Eskola in 1921, with refinements based on subsequent experimental work. Eskola drew upon the zonal schemes, based on index minerals, that were pioneered by the British geologist, George Barrow . Atom Atoms are

1800-457: A rare type of magma called a carbonatite that is highly enriched in carbonates and low in silica . Cooling bodies of carbonatite magma give off highly alkaline fluids rich in sodium as they solidify, and the hot, reactive fluid replaces much of the mineral content in the aureole with sodium-rich minerals. A special type of contact metamorphism, associated with fossil fuel fires, is known as pyrometamorphism . Hydrothermal metamorphism

1920-552: A series of experiments in which they bombarded thin foils of metal with a beam of alpha particles . They did this to measure the scattering patterns of the alpha particles. They spotted a small number of alpha particles being deflected by angles greater than 90°. This shouldn't have been possible according to the Thomson model of the atom, whose charges were too diffuse to produce a sufficiently strong electric field. The deflections should have all been negligible. Rutherford proposed that

2040-519: A set of atomic numbers, from the single-proton element hydrogen up to the 118-proton element oganesson . All known isotopes of elements with atomic numbers greater than 82 are radioactive, although the radioactivity of element 83 ( bismuth ) is so slight as to be practically negligible. About 339 nuclides occur naturally on Earth , of which 251 (about 74%) have not been observed to decay, and are referred to as " stable isotopes ". Only 90 nuclides are stable theoretically , while another 161 (bringing

2160-472: A short-ranged attractive potential called the residual strong force . At distances smaller than 2.5 fm this force is much more powerful than the electrostatic force that causes positively charged protons to repel each other. Atoms of the same element have the same number of protons, called the atomic number . Within a single element, the number of neutrons may vary, determining the isotope of that element. The total number of protons and neutrons determine

2280-440: A size that is too small to be measured using available techniques. It was the lightest particle with a positive rest mass measured, until the discovery of neutrino mass. Under ordinary conditions, electrons are bound to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as

2400-432: A tiny atomic nucleus , and are collectively called nucleons . The radius of a nucleus is approximately equal to 1.07 A 3 {\displaystyle 1.07{\sqrt[{3}]{A}}}   femtometres , where A {\displaystyle A} is the total number of nucleons. This is much smaller than the radius of the atom, which is on the order of 10  fm. The nucleons are bound together by

2520-434: A whole. If an atom has more electrons than protons, then it has an overall negative charge, and is called a negative ion (or anion). Conversely, if it has more protons than electrons, it has a positive charge, and is called a positive ion (or cation). The electrons of an atom are attracted to the protons in an atomic nucleus by the electromagnetic force . The protons and neutrons in the nucleus are attracted to each other by

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2640-470: A whole; a charged atom is called an ion . Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson ; see history of subatomic physics for details. Protons have a positive charge and a mass of 1.6726 × 10  kg . The number of protons in an atom is called its atomic number . Ernest Rutherford (1919) observed that nitrogen under alpha-particle bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that

2760-499: Is 29.5% nitrogen and 70.5% oxygen. Adjusting these figures, in nitrous oxide there is 80 g of oxygen for every 140 g of nitrogen, in nitric oxide there is about 160 g of oxygen for every 140 g of nitrogen, and in nitrogen dioxide there is 320 g of oxygen for every 140 g of nitrogen. 80, 160, and 320 form a ratio of 1:2:4. The respective formulas for these oxides are N 2 O , NO , and NO 2 . In 1897, J. J. Thomson discovered that cathode rays are not

2880-427: Is 88.1% tin and 11.9% oxygen, and the other is a white powder that is 78.7% tin and 21.3% oxygen. Adjusting these figures, in the grey powder there is about 13.5 g of oxygen for every 100 g of tin, and in the white powder there is about 27 g of oxygen for every 100 g of tin. 13.5 and 27 form a ratio of 1:2. Dalton concluded that in the grey oxide there is one atom of oxygen for every atom of tin, and in

3000-415: Is a common result of metamorphism, rock that is intensely deformed may eliminate strain energy by recrystallizing as a fine-grained rock called mylonite . Certain kinds of rock, such as those rich in quartz, carbonate minerals , or olivine, are particularly prone to form mylonites, while feldspar and garnet are resistant to mylonitization. Phase change metamorphism is the creating of a new mineral with

3120-480: Is a general term for metamorphism that affects entire regions of the Earth's crust. It most often refers to dynamothermal metamorphism , which takes place in orogenic belts (regions where mountain building is taking place), but also includes burial metamorphism , which results simply from rock being buried to great depths below the Earth's surface in a subsiding basin. To many geologists, regional metamorphism

3240-408: Is a measure of the distance out to which the electron cloud extends from the nucleus. This assumes the atom to exhibit a spherical shape, which is only obeyed for atoms in vacuum or free space. Atomic radii may be derived from the distances between two nuclei when the two atoms are joined in a chemical bond . The radius varies with the location of an atom on the atomic chart, the type of chemical bond,

3360-573: Is affected by the ratio of protons to neutrons, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and filled quantum shells. These quantum shells correspond to a set of energy levels within the shell model of the nucleus; filled shells, such as the filled shell of 50 protons for tin, confers unusual stability on the nuclide. Of the 251 known stable nuclides, only four have both an odd number of protons and odd number of neutrons: hydrogen-2 ( deuterium ), lithium-6 , boron-10 , and nitrogen-14 . ( Tantalum-180m

3480-459: Is an important medium through which atoms are exchanged. This permits recrystallization of existing minerals or crystallization of new minerals with different crystalline structures or chemical compositions (neocrystallization). The transformation converts the minerals in the protolith into forms that are more stable (closer to chemical equilibrium ) under the conditions of pressure and temperature at which metamorphism takes place. Metamorphism

3600-664: Is called the metamorphic aureole , the contact aureole , or simply the aureole. Contact metamorphic rocks are usually known as hornfels . Rocks formed by contact metamorphism may not present signs of strong deformation and are often fine-grained and extremely tough. The Yule Marble used on the Lincoln Memorial exterior and the Tomb of the Unknown Soldier in Arlington National Cemetery

3720-697: Is completed during early stages of metamorphism. For a sandstone protolith, the dividing line between diagenesis and metamorphism can be placed at the point where strained quartz grains begin to be replaced by new, unstrained, small quartz grains, producing a mortar texture that can be identified in thin sections under a polarizing microscope. With increasing grade of metamorphism, further recrystallization produces foam texture , characterized by polygonal grains meeting at triple junctions, and then porphyroblastic texture , characterized by coarse, irregular grains, including some larger grains ( porphyroblasts .) Metamorphic rocks are typically more coarsely crystalline than

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3840-488: Is composed of mylonite. Mylonite is distinguished by its strong foliation, which is absent in most cataclastic rock. It is distinguished from the surrounding rock by its finer grain size. There is considerable evidence that cataclasites form as much through plastic deformation and recrystallization as brittle fracture of grains, and that the rock may never fully lose cohesion during the process. Different minerals become ductile at different temperatures, with quartz being among

3960-451: Is generally regarded to begin at temperatures of 100 to 200 °C (212 to 392 °F). This excludes diagenetic changes due to compaction and lithification , which result in the formation of sedimentary rocks. The upper boundary of metamorphic conditions lies at the solidus of the rock, which is the temperature at which the rock begins to melt. At this point, the process becomes an igneous process. The solidus temperature depends on

4080-438: Is higher than its proton number, so Rutherford hypothesized that the surplus weight was carried by unknown particles with no electric charge and a mass equal to that of the proton. In 1928, Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles. It was later discovered that this radiation could knock hydrogen atoms out of paraffin wax . Initially it

4200-507: Is known as prograde metamorphism , while decreasing temperature and pressure characterize retrograde metamorphism . Metamorphic petrology is the study of metamorphism. Metamorphic petrologists rely heavily on statistical mechanics and experimental petrology to understand metamorphic processes. Metamorphism is the set of processes by which existing rock is transformed physically or chemically at elevated temperature, without actually melting to any great degree. The importance of heating in

4320-429: Is mediated by gluons . The protons and neutrons, in turn, are held to each other in the nucleus by the nuclear force , which is a residuum of the strong force that has somewhat different range-properties (see the article on the nuclear force for more). The gluon is a member of the family of gauge bosons , which are elementary particles that mediate physical forces. All the bound protons and neutrons in an atom make up

4440-481: Is not based on these old concepts. In the early 19th century, the scientist John Dalton found evidence that matter really is composed of discrete units, and so applied the word atom to those units. In the early 1800s, John Dalton compiled experimental data gathered by him and other scientists and discovered a pattern now known as the " law of multiple proportions ". He noticed that in any group of chemical compounds which all contain two particular chemical elements,

4560-425: Is not possible due to quantum effects . More than 99.9994% of an atom's mass is in the nucleus. Protons have a positive electric charge and neutrons have no charge, so the nucleus is positively charged. The electrons are negatively charged, and this opposing charge is what binds them to the nucleus. If the numbers of protons and electrons are equal, as they normally are, then the atom is electrically neutral as

4680-502: Is odd-odd and observationally stable, but is predicted to decay with a very long half-life.) Also, only four naturally occurring, radioactive odd-odd nuclides have a half-life over a billion years: potassium-40 , vanadium-50 , lanthanum-138 , and lutetium-176 . Most odd-odd nuclei are highly unstable with respect to beta decay , because the decay products are even-even, and are therefore more strongly bound, due to nuclear pairing effects . The large majority of an atom's mass comes from

4800-410: Is practically synonymous with dynamothermal metamorphism. This form of metamorphism takes place at convergent plate boundaries , where two continental plates or a continental plate and an island arc collide. The collision zone becomes a belt of mountain formation called an orogeny . The orogenic belt is characterized by thickening of the Earth's crust, during which the deeply buried crustal rock

4920-477: Is required to bring them together. It is this energy-releasing process that makes nuclear fusion in stars a self-sustaining reaction. For heavier nuclei, the binding energy per nucleon begins to decrease. That means that a fusion process producing a nucleus that has an atomic number higher than about 26, and a mass number higher than about 60, is an endothermic process . Thus, more massive nuclei cannot undergo an energy-producing fusion reaction that can sustain

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5040-455: Is responsible for most of the physical changes observed in nature. Chemistry is the science that studies these changes. The basic idea that matter is made up of tiny indivisible particles is an old idea that appeared in many ancient cultures. The word atom is derived from the ancient Greek word atomos , which means "uncuttable". But this ancient idea was based in philosophical reasoning rather than scientific reasoning. Modern atomic theory

5160-539: Is subjected to high temperatures and pressures and is intensely deformed. Subsequent erosion of the mountains exposes the roots of the orogenic belt as extensive outcrops of metamorphic rock, characteristic of mountain chains. Metamorphic rock formed in these settings tends to shown well-developed foliation . Foliation develops when a rock is being shortened along one axis during metamorphism. This causes crystals of platy minerals, such as mica and chlorite , to become rotated such that their short axes are parallel to

5280-421: Is that an accelerating charged particle radiates electromagnetic radiation, causing the particle to lose kinetic energy. Circular motion counts as acceleration, which means that an electron orbiting a central charge should spiral down into that nucleus as it loses speed. In 1913, the physicist Niels Bohr proposed a new model in which the electrons of an atom were assumed to orbit the nucleus but could only do so in

5400-470: Is the mass loss and c is the speed of light . This deficit is part of the binding energy of the new nucleus, and it is the non-recoverable loss of the energy that causes the fused particles to remain together in a state that requires this energy to separate. The fusion of two nuclei that create larger nuclei with lower atomic numbers than iron and nickel —a total nucleon number of about 60—is usually an exothermic process that releases more energy than

5520-430: Is the most recognized metamorphic series in the world. However, Barrovian metamorphism is specific to pelitic rock, formed from mudstone or siltstone , and it is not unique even in pelitic rock. A different sequence in the northeast of Scotland defines Buchan metamorphism , which took place at lower pressure than the Barrovian. Burial metamorphism takes place simply through rock being buried to great depths below

5640-460: Is the passing of electrons from one atom to the next, and when there was no current the electrons embedded themselves in the atoms. This in turn meant that atoms were not indivisible as scientists thought. The atom was composed of electrons whose negative charge was balanced out by some source of positive charge to create an electrically neutral atom. Ions, Thomson explained, must be atoms which have an excess or shortage of electrons. The electrons in

5760-401: Is the result of the interaction of a rock with a high-temperature fluid of variable composition. The difference in composition between an existing rock and the invading fluid triggers a set of metamorphic and metasomatic reactions. The hydrothermal fluid may be magmatic (originate in an intruding magma), circulating groundwater , or ocean water. Convective circulation of hydrothermal fluids in

5880-552: The Loch Ness Supergroup . The lithologies of these rocks suggest deposition in shallow marine conditions. Metamorphism Various forms of metamorphism exist, including regional , contact , hydrothermal , shock , and dynamic metamorphism. These differ in the characteristic temperatures, pressures, and rate at which they take place and in the extent to which reactive fluids are involved. Metamorphism occurring at increasing pressure and temperature conditions

6000-491: The Schroedinger equation , which describes electrons as three-dimensional waveforms rather than points in space. A consequence of using waveforms to describe particles is that it is mathematically impossible to obtain precise values for both the position and momentum of a particle at a given point in time. This became known as the uncertainty principle , formulated by Werner Heisenberg in 1927. In this concept, for

6120-438: The hydrostatic equilibrium of a star. The electrons in an atom are attracted to the protons in the nucleus by the electromagnetic force . This force binds the electrons inside an electrostatic potential well surrounding the smaller nucleus, which means that an external source of energy is needed for the electron to escape. The closer an electron is to the nucleus, the greater the attractive force. Hence electrons bound near

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6240-547: The nuclear force . This force is usually stronger than the electromagnetic force that repels the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force. In this case, the nucleus splits and leaves behind different elements . This is a form of nuclear decay . Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules or crystals . The ability of atoms to attach and detach from each other

6360-472: The nuclide . The number of neutrons relative to the protons determines the stability of the nucleus, with certain isotopes undergoing radioactive decay . The proton, the electron, and the neutron are classified as fermions . Fermions obey the Pauli exclusion principle which prohibits identical fermions, such as multiple protons, from occupying the same quantum state at the same time. Thus, every proton in

6480-517: The 'surface' of these particles is not sharply defined. The neutron was discovered in 1932 by the English physicist James Chadwick . In the Standard Model of physics, electrons are truly elementary particles with no internal structure, whereas protons and neutrons are composite particles composed of elementary particles called quarks . There are two types of quarks in atoms, each having

6600-758: The Badenoch Group within the Moine Supergroup whilst others described them as simply ‘Moine-like’. Detrital zircon geochronology has allowed the group to be correlated with the Glennfinnan and Loch Eil groups as they all contain zircons that are younger than 950 Ma (million years ago), showing that they postdate the Renlandian Orogeny , a tectonic and thermal event that affected the Morar Group . The group has now been assigned to

6720-419: The Earth's surface in a subsiding basin. Here the rock is subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. Burial metamorphism tends to produce low-grade metamorphic rock. This shows none of the effects of deformation and folding so characteristic of dynamothermal metamorphism. Examples of metamorphic rocks formed by burial metamorphism include some of

6840-452: The Earth's surface. Impact metamorphism is, therefore, characterized by ultrahigh pressure conditions and low temperature. The resulting minerals (such as SiO 2 polymorphs coesite and stishovite ) and textures are characteristic of these conditions. Dynamic metamorphism is associated with zones of high strain such as fault zones. In these environments, mechanical deformation is more important than chemical reactions in transforming

6960-681: The Great Glen and Ericht-Laidon fault belts though their margins are hidden beneath younger strata; Old Red Sandstone to the north and west and Grampian Group rocks elsewhere. The succession is divided into two subgroups; the Dava Subgroup (previously referred to as the Dava Succession) and the Glen Banchor Subgroup. The former, named from the locality of Dava between Inverness and Grantown-on-Spey includes

7080-573: The Slochd Psammite and Flichity Semipelite formations. The latter is named for Glen Banchor, west of Newtonmore , the type area being from here to Laggan. The Glen Banchor sequence is believed to be between 1 and 1.5 km thick and unconformably overlain by rocks of the Grampian and Appin groups, though the boundary may be tectonic in nature. Long the subject of debate as to how they relate to surrounding rock sequences, some geologists placed

7200-401: The albite-epidote hornfels is often not formed, even though it is the lowest temperature grade. Magmatic fluids coming from the intrusive rock may also take part in the metamorphic reactions . An extensive addition of magmatic fluids can significantly modify the chemistry of the affected rocks. In this case the metamorphism grades into metasomatism . If the intruded rock is rich in carbonate

7320-399: The amount of Element A per measure of Element B will differ across these compounds by ratios of small whole numbers. This pattern suggested that each element combines with other elements in multiples of a basic unit of weight, with each element having a unit of unique weight. Dalton decided to call these units "atoms". For example, there are two types of tin oxide : one is a grey powder that

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7440-441: The appearance of key minerals in rocks of pelitic (shaly, aluminous) origin: Low grade ------------------- Intermediate --------------------- High grade A more complete indication of this intensity or degree is provided by the concept of metamorphic facies . Metamorphic facies are recognizable terranes or zones with an assemblage of key minerals that were in equilibrium under specific range of temperature and pressure during

7560-444: The atom logically had to be balanced out by a commensurate amount of positive charge, but Thomson had no idea where this positive charge came from, so he tentatively proposed that it was everywhere in the atom, the atom being in the shape of a sphere. This was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. Following from this, Thomson imagined that the balance of electrostatic forces would distribute

7680-422: The atomic mass unit (for example the mass of a nitrogen-14 is roughly 14 Da), but this number will not be exactly an integer except (by definition) in the case of carbon-12. The heaviest stable atom is lead-208, with a mass of 207.976 6521  Da . As even the most massive atoms are far too light to work with directly, chemists instead use the unit of moles . One mole of atoms of any element always has

7800-491: The atomic weights of many elements were multiples of hydrogen's atomic weight, which is in fact true for all of them if one takes isotopes into account. In 1898, J. J. Thomson found that the positive charge of a hydrogen ion is equal to the negative charge of an electron, and these were then the smallest known charged particles. Thomson later found that the positive charge in an atom is a positive multiple of an electron's negative charge. In 1913, Henry Moseley discovered that

7920-515: The aureoles around batholiths can be up to several kilometers wide. The metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole. This is usually related to the metamorphic temperatures of pelitic or aluminosilicate rocks and the minerals they form. The metamorphic grades of aureoles at shallow depth are albite - epidote hornfels, hornblende hornfels, pyroxene hornfels, and sillimanite hornfels, in increasing order of temperature of formation. However,

8040-412: The basic particles of the chemical elements . An atom consists of a nucleus of protons and generally neutrons , surrounded by an electromagnetically bound swarm of electrons . The chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium , and any atom that contains 29 protons is copper . Atoms with

8160-413: The center of the potential well require more energy to escape than those at greater separations. Electrons, like other particles, have properties of both a particle and a wave . The electron cloud is a region inside the potential well where each electron forms a type of three-dimensional standing wave —a wave form that does not move relative to the nucleus. This behavior is defined by an atomic orbital ,

8280-478: The chemical elements, at least one stable isotope exists. As a rule, there is only a handful of stable isotopes for each of these elements, the average being 3.1 stable isotopes per element. Twenty-six " monoisotopic elements " have only a single stable isotope, while the largest number of stable isotopes observed for any element is ten, for the element tin . Elements 43 , 61 , and all elements numbered 83 or higher have no stable isotopes. Stability of isotopes

8400-454: The composition of the rock, the pressure, and whether the rock is saturated with water. Typical solidus temperatures range from 650 °C (1,202 °F) for wet granite at a few hundred megapascals (MPa) of pressure to about 1,080 °C (1,980 °F) for wet basalt at atmospheric pressure. Migmatites are rocks formed at this upper limit, which contains pods and veins of material that has started to melt but has not fully segregated from

8520-453: The core of the Sun protons require energies of 3 to 10 keV to overcome their mutual repulsion—the coulomb barrier —and fuse together into a single nucleus. Nuclear fission is the opposite process, causing a nucleus to split into two smaller nuclei—usually through radioactive decay. The nucleus can also be modified through bombardment by high energy subatomic particles or photons. If this modifies

8640-550: The crystals, while high pressures cause solution of the crystals within the rock at their points of contact ( pressure solution ) and redeposition in pore space. During recrystallization, the identity of the mineral does not change, only its texture. Recrystallization generally begins when temperatures reach above half the melting point of the mineral on the Kelvin scale. Pressure solution begins during diagenesis (the process of lithification of sediments into sedimentary rock) but

8760-400: The depth at which they were formed, as the temperature and confining pressure determine the deformation mechanisms which predominate. At the shallowest depths, a fault zone will be filled with various kinds of unconsolidated cataclastic rock , such as fault gouge or fault breccia . At greater depths, these are replaced by consolidated cataclastic rock, such as crush breccia , in which

8880-418: The direction of shortening. This results in a banded, or foliated, rock, with the bands showing the colors of the minerals that formed them. Foliated rock often develops planes of cleavage . Slate is an example of a foliated metamorphic rock, originating from shale , and it typically shows well-developed cleavage that allows slate to be split into thin plates. The type of foliation that develops depends on

9000-512: The electrons throughout the sphere in a more or less even manner. Thomson's model is popularly known as the plum pudding model , though neither Thomson nor his colleagues used this analogy. Thomson's model was incomplete, it was unable to predict any other properties of the elements such as emission spectra and valencies . It was soon rendered obsolete by the discovery of the atomic nucleus . Between 1908 and 1913, Ernest Rutherford and his colleagues Hans Geiger and Ernest Marsden performed

9120-506: The energies of the quantum states, are responsible for atomic spectral lines . The amount of energy needed to remove or add an electron—the electron binding energy —is far less than the binding energy of nucleons . For example, it requires only 13.6 eV to strip a ground-state electron from a hydrogen atom, compared to 2.23  million eV for splitting a deuterium nucleus. Atoms are electrically neutral if they have an equal number of protons and electrons. Atoms that have either

9240-671: The energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles which could not be massless like the gamma ray, but instead were required to have a mass similar to that of a proton. Chadwick now claimed these particles as Rutherford's neutrons. In 1925, Werner Heisenberg published the first consistent mathematical formulation of quantum mechanics ( matrix mechanics ). One year earlier, Louis de Broglie had proposed that all particles behave like waves to some extent, and in 1926 Erwin Schroedinger used this idea to develop

9360-399: The first to become ductile, and sheared rock composed of different minerals may simultaneously show both plastic deformation and brittle fracture. The strain rate also affects the way in which rocks deform. Ductile deformation is more likely at low strain rates (less than 10 sec ) in the middle and lower crust, but high strain rates can cause brittle deformation. At the highest strain rates,

9480-470: The formation of metamorphic rock was first recognized by the pioneering Scottish naturalist, James Hutton , who is often described as the father of modern geology. Hutton wrote in 1795 that some rock beds of the Scottish Highlands had originally been sedimentary rock , but had been transformed by great heat. Hutton also speculated that pressure was important in metamorphism. This hypothesis

9600-433: The frequencies of X-ray emissions from an excited atom were a mathematical function of its atomic number and hydrogen's nuclear charge. In 1919 Rutherford bombarded nitrogen gas with alpha particles and detected hydrogen ions being emitted from the gas, and concluded that they were produced by alpha particles hitting and splitting the nuclei of the nitrogen atoms. These observations led Rutherford to conclude that

9720-416: The hydrogen nucleus is a distinct particle within the atom and named it proton . Neutrons have no electrical charge and have a mass of 1.6749 × 10  kg . Neutrons are the heaviest of the three constituent particles, but their mass can be reduced by the nuclear binding energy . Neutrons and protons (collectively known as nucleons ) have comparable dimensions—on the order of 2.5 × 10  m —although

9840-445: The hydrogen nucleus is a singular particle with a positive charge equal to the electron's negative charge. He named this particle " proton " in 1920. The number of protons in an atom (which Rutherford called the " atomic number " ) was found to be equal to the element's ordinal number on the periodic table and therefore provided a simple and clear-cut way of distinguishing the elements from each other. The atomic weight of each element

9960-403: The larger rock fragments are cemented together by calcite or quartz. At depths greater than about 5 kilometers (3.1 mi), cataclasites appear; these are quite hard rocks consist of crushed rock fragments in a flinty matrix, which forms only at elevated temperature. At still greater depths, where temperatures exceed 300 °C (572 °F), plastic deformation takes over, and the fault zone

10080-452: The list of processes that help bring about metamorphism. However, metamorphism can take place without metasomatism (isochemical metamorphism) or at depths of just a few hundred meters where pressures are relatively low (for example, in contact metamorphism). Rock can be transformed without melting because heat causes atomic bonds to break, freeing the atoms to move and form new bonds with other atoms . Pore fluid present between mineral grains

10200-502: The metamorphic grade. For instance, starting with a mudstone , the following sequence develops with increasing temperature: The mudstone is first converted to slate, which is a very fine-grained, foliated metamorphic rock, characteristic of very low grade metamorphism. Slate in turn is converted to phyllite , which is fine-grained and found in areas of low grade metamorphism. Schist is medium to coarse-grained and found in areas of medium grade metamorphism. High-grade metamorphism transforms

10320-407: The metamorphic rock marble . In metamorphosed sandstone , recrystallization of the original quartz sand grains results in very compact quartzite , also known as metaquartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing

10440-432: The mutual repulsion of the protons requires an increasing proportion of neutrons to maintain the stability of the nucleus. The number of protons and neutrons in the atomic nucleus can be modified, although this can require very high energies because of the strong force. Nuclear fusion occurs when multiple atomic particles join to form a heavier nucleus, such as through the energetic collision of two nuclei. For example, at

10560-509: The nucleus must occupy a quantum state different from all other protons, and the same applies to all neutrons of the nucleus and to all electrons of the electron cloud. A nucleus that has a different number of protons than neutrons can potentially drop to a lower energy state through a radioactive decay that causes the number of protons and neutrons to more closely match. As a result, atoms with matching numbers of protons and neutrons are more stable against decay, but with increasing atomic number,

10680-515: The nucleus to emit particles or electromagnetic radiation. Radioactivity can occur when the radius of a nucleus is large compared with the radius of the strong force, which only acts over distances on the order of 1 fm. The most common forms of radioactive decay are: Other more rare types of radioactive decay include ejection of neutrons or protons or clusters of nucleons from a nucleus, or more than one beta particle . An analog of gamma emission which allows excited nuclei to lose energy in

10800-401: The number of hydrogen atoms. A single carat diamond with a mass of 2 × 10  kg contains about 10 sextillion (10 ) atoms of carbon . If an apple were magnified to the size of the Earth, then the atoms in the apple would be approximately the size of the original apple. Every element has one or more isotopes that have unstable nuclei that are subject to radioactive decay, causing

10920-450: The number of neighboring atoms ( coordination number ) and a quantum mechanical property known as spin . On the periodic table of the elements, atom size tends to increase when moving down columns, but decrease when moving across rows (left to right). Consequently, the smallest atom is helium with a radius of 32  pm , while one of the largest is caesium at 225 pm. When subjected to external forces, like electrical fields ,

11040-451: The number of protons in a nucleus, the atom changes to a different chemical element. If the mass of the nucleus following a fusion reaction is less than the sum of the masses of the separate particles, then the difference between these two values can be emitted as a type of usable energy (such as a gamma ray , or the kinetic energy of a beta particle ), as described by Albert Einstein 's mass–energy equivalence formula, E=mc , where m

11160-449: The ocean floor basalts produces extensive hydrothermal metamorphism adjacent to spreading centers and other submarine volcanic areas. The fluids eventually escape through vents on the ocean floor known as black smokers . The patterns of this hydrothermal alteration are used as a guide in the search for deposits of valuable metal ores. Shock metamorphism occurs when an extraterrestrial object (a meteorite for instance) collides with

11280-438: The overlying mantle, where it lowers the melting temperature of the mantle rock, generating magma via flux melting . The mantle-derived magmas can ultimately reach the Earth's surface, resulting in volcanic eruptions. The resulting arc volcanoes tend to produce dangerous eruptions, because their high water content makes them extremely explosive. Examples of dehydration reactions that release water include: An example of

11400-435: The positive charge of the atom is concentrated in a tiny volume at the center of the atom and that the electrons surround this nucleus in a diffuse cloud. This nucleus carried almost all of the atom's mass, the electrons being so very light. Only such an intense concentration of charge, anchored by its high mass, could produce an electric field that could deflect the alpha particles so strongly. A problem in classical mechanics

11520-401: The protolith from which they formed. Atoms in the interior of a crystal are surrounded by a stable arrangement of neighboring atoms. This is partially missing at the surface of the crystal, producing a surface energy that makes the surface thermodynamically unstable. Recrystallization to coarser crystals reduces the surface area and so minimizes the surface energy. Although grain coarsening

11640-516: The protolith. Chemical reactions digest the minerals of the protolith which yields new minerals. This is a very slow process as it can also involve the diffusion of atoms through solid crystals. An example of a neocrystallization reaction is the reaction of fayalite with plagioclase at elevated pressure and temperature to form garnet . The reaction is: Many complex high-temperature reactions may take place between minerals without them melting, and each mineral assemblage produced provides us with

11760-448: The protons and neutrons that make it up. The total number of these particles (called "nucleons") in a given atom is called the mass number . It is a positive integer and dimensionless (instead of having dimension of mass), because it expresses a count. An example of use of a mass number is "carbon-12," which has 12 nucleons (six protons and six neutrons). The actual mass of an atom at rest is often expressed in daltons (Da), also called

11880-421: The red powder there is about 42 g of oxygen for every 100 g of iron. 28 and 42 form a ratio of 2:3. Dalton concluded that in these oxides, for every two atoms of iron, there are two or three atoms of oxygen respectively ( Fe 2 O 2 and Fe 2 O 3 ). As a final example: nitrous oxide is 63.3% nitrogen and 36.7% oxygen, nitric oxide is 44.05% nitrogen and 55.95% oxygen, and nitrogen dioxide

12000-435: The refractory residue. The metamorphic process can occur at almost any pressure, from near surface pressure (for contact metamorphism) to pressures in excess of 16 kbar (1600 MPa). The change in the grain size and orientation in the rock during the process of metamorphism is called recrystallization . For instance, the small calcite crystals in the sedimentary rocks limestone and chalk change into larger crystals in

12120-437: The result is a skarn . Fluorine -rich magmatic waters which leave a cooling granite may often form greisens within and adjacent to the contact of the granite. Metasomatic altered aureoles can localize the deposition of metallic ore minerals and thus are of economic interest. Fenitization , or Na-metasomatism , is a distinctive form of contact metamorphism accompanied by metasomatism. It takes place around intrusions of

12240-413: The rock may be so strongly heated that it briefly melts, forming a glassy rock called pseudotachylite . Pseudotachylites seem to be restricted to dry rock, such as granulite. Metamorphic rocks are classified by their protolith, if this can be determined from the properties of the rock itself. For example, if examination of a metamorphic rock shows that its protolith was basalt, it will be described as

12360-428: The rock to gneiss , which is coarse to very coarse-grained. Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated. Marble lacks platy minerals and is generally not foliated, which allows its use as a material for sculpture and architecture. Collisional orogenies are preceded by subduction of oceanic crust. The conditions within

12480-548: The rock. The minerals present in the rock often do not reflect conditions of chemical equilibrium, and the textures produced by dynamic metamorphism are more significant than the mineral makeup. There are three deformation mechanisms by which rock is mechanically deformed. These are cataclasis , the deformation of rock via the fracture and rotation of mineral grains; plastic deformation of individual mineral crystals; and movement of individual atoms by diffusive processes. The textures of dynamic metamorphic zones are dependent on

12600-607: The rocks of the Midcontinent Rift System of North America, such as the Sioux Quartzite , and in the Hamersley Basin of Australia. Contact metamorphism occurs typically around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock . The area surrounding the intrusion where the contact metamorphism effects are present

12720-412: The same chemical element . Atoms with equal numbers of protons but a different number of neutrons are different isotopes of the same element. For example, all hydrogen atoms admit exactly one proton, but isotopes exist with no neutrons ( hydrogen-1 , by far the most common form, also called protium), one neutron ( deuterium ), two neutrons ( tritium ) and more than two neutrons . The known elements form

12840-500: The same chemical formula as a mineral of the protolith. This involves a rearrangement of the atoms in the crystals. An example is provided by the aluminium silicate minerals, kyanite , andalusite , and sillimanite . All three have the identical composition, Al 2 SiO 5 . Kyanite is stable at surface conditions. However, at atmospheric pressure, kyanite transforms to andalusite at a temperature of about 190 °C (374 °F). Andalusite, in turn, transforms to sillimanite when

12960-498: The same number of atoms (about 6.022 × 10 ). This number was chosen so that if an element has an atomic mass of 1 u, a mole of atoms of that element has a mass close to one gram. Because of the definition of the unified atomic mass unit , each carbon-12 atom has an atomic mass of exactly 12 Da, and so a mole of carbon-12 atoms weighs exactly 0.012 kg. Atoms lack a well-defined outer boundary, so their dimensions are usually described in terms of an atomic radius . This

13080-448: The same number of protons but a different number of neutrons are called isotopes of the same element. Atoms are extremely small, typically around 100  picometers across. A human hair is about a million carbon atoms wide. Atoms are smaller than the shortest wavelength of visible light, which means humans cannot see atoms with conventional microscopes. They are so small that accurately predicting their behavior using classical physics

13200-539: The shape of an atom may deviate from spherical symmetry . The deformation depends on the field magnitude and the orbital type of outer shell electrons, as shown by group-theoretical considerations. Aspherical deviations might be elicited for instance in crystals , where large crystal-electrical fields may occur at low-symmetry lattice sites. Significant ellipsoidal deformations have been shown to occur for sulfur ions and chalcogen ions in pyrite -type compounds. Atomic dimensions are thousands of times smaller than

13320-414: The subducting slab as it plunges toward the mantle in a subduction zone produce their own distinctive regional metamorphic effects , characterized by paired metamorphic belts . The pioneering work of George Barrow on regional metamorphism in the Scottish Highlands showed that some regional metamorphism produces well-defined, mappable zones of increasing metamorphic grade. This Barrovian metamorphism

13440-426: The temperature reaches about 800 °C (1,470 °F). At pressures above about 4 kbar (400 MPa), kyanite transforms directly to sillimanite as the temperature increases. A similar phase change is sometimes seen between calcite and aragonite , with calcite transforming to aragonite at elevated pressure and relatively low temperature. Neocrystallization involves the creation of new mineral crystals different from

13560-737: The total to 251) have not been observed to decay, even though in theory it is energetically possible. These are also formally classified as "stable". An additional 35 radioactive nuclides have half-lives longer than 100 million years, and are long-lived enough to have been present since the birth of the Solar System . This collection of 286 nuclides are known as primordial nuclides . Finally, an additional 53 short-lived nuclides are known to occur naturally, as daughter products of primordial nuclide decay (such as radium from uranium ), or as products of natural energetic processes on Earth, such as cosmic ray bombardment (for example, carbon-14). For 80 of

13680-445: The unified atomic mass unit (u). This unit is defined as a twelfth of the mass of a free neutral atom of carbon-12 , which is approximately 1.66 × 10  kg . Hydrogen-1 (the lightest isotope of hydrogen which is also the nuclide with the lowest mass) has an atomic weight of 1.007825 Da. The value of this number is called the atomic mass . A given atom has an atomic mass approximately equal (within 1%) to its mass number times

13800-406: The wavelengths of light (400–700  nm ) so they cannot be viewed using an optical microscope , although individual atoms can be observed using a scanning tunneling microscope . To visualize the minuteness of the atom, consider that a typical human hair is about 1 million carbon atoms in width. A single drop of water contains about 2  sextillion ( 2 × 10 ) atoms of oxygen, and twice

13920-432: The white oxide there are two atoms of oxygen for every atom of tin ( SnO and SnO 2 ). Dalton also analyzed iron oxides . There is one type of iron oxide that is a black powder which is 78.1% iron and 21.9% oxygen; and there is another iron oxide that is a red powder which is 70.4% iron and 29.6% oxygen. Adjusting these figures, in the black powder there is about 28 g of oxygen for every 100 g of iron, and in

14040-407: The word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles . The constituent particles of an atom are the electron , the proton and the neutron . The electron is the least massive of these particles by four orders of magnitude at 9.11 × 10  kg , with a negative electrical charge and

14160-419: Was formed by contact metamorphism. 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, extending not more than one or two dike thicknesses into the surrounding rock, whereas

14280-422: Was tested by his friend, James Hall , who sealed chalk into a makeshift pressure vessel constructed from a cannon barrel and heated it in an iron foundry furnace. Hall found that this produced a material strongly resembling marble , rather than the usual quicklime produced by heating of chalk in the open air. French geologists subsequently added metasomatism , the circulation of fluids through buried rock, to

14400-432: Was thought to be high-energy gamma radiation , since gamma radiation had a similar effect on electrons in metals, but James Chadwick found that the ionization effect was too strong for it to be due to electromagnetic radiation, so long as energy and momentum were conserved in the interaction. In 1932, Chadwick exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring

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