A volcanic arc (also known as a magmatic arc ) is a belt of volcanoes formed above a subducting oceanic tectonic plate , with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench , with the arc located further from the subducting plate than the trench. The oceanic plate is saturated with water, mostly in the form of hydrous minerals such as micas , amphiboles , and serpentines . As the oceanic plate is subducted, it is subjected to increasing pressure and temperature with increasing depth. The heat and pressure break down the hydrous minerals in the plate, releasing water into the overlying mantle. Volatiles such as water drastically lower the melting point of the mantle , causing some of the mantle to melt and form magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.
96-413: Volcanic arcs are distinct from volcanic chains formed over hotspots in the middle of a tectonic plate. Volcanoes often form one after another as the plate moves over the hotspot, and so the volcanoes progress in age from one end of the chain to the other. The Hawaiian Islands form a typical hotspot chain, with the older islands to the northwest and Hawaii Island itself, which is just 400,000 years old, at
192-484: A colloidal mixture of the metal and caesium chloride. The electrolysis of the aqueous solution of chloride with a mercury cathode produced a caesium amalgam which readily decomposed under the aqueous conditions. The pure metal was eventually isolated by the Swedish chemist Carl Setterberg while working on his doctorate with Kekulé and Bunsen. In 1882, he produced caesium metal by electrolysing caesium cyanide , avoiding
288-407: A spectroscope , which had been invented by Bunsen and Kirchhoff only a year previously. To obtain a pure sample of caesium, 44,000 litres (9,700 imp gal; 12,000 US gal) of mineral water had to be evaporated to yield 240 kilograms (530 lb) of concentrated salt solution. The alkaline earth metals were precipitated either as sulfates or oxalates , leaving the alkali metal in
384-470: A tectonic plate composed of relatively thin, dense oceanic lithosphere sinks into the Earth's mantle beneath a less dense overriding plate. The overriding plate may be either another oceanic plate or a continental plate. The subducting plate, or slab , sinks into the mantle at an angle, so that there is a wedge of mantle between the slab and the overriding plate. The boundary between the subducting plate and
480-431: A blue or violet colour. Caesium exists in the form of different allotropes , one of them a dimer called dicaesium. Caesium metal is highly reactive and pyrophoric . It ignites spontaneously in air, and reacts explosively with water even at low temperatures, more so than the other alkali metals . It reacts with ice at temperatures as low as −116 °C (−177 °F). Because of this high reactivity, caesium metal
576-442: A dilute chloride (CsCl) solution. This solution can be evaporated to produce caesium chloride or transformed into caesium alum or caesium carbonate. Though not commercially feasible, the ore can be directly reduced with potassium, sodium, or calcium in vacuum to produce caesium metal directly. Most of the mined caesium (as salts) is directly converted into caesium formate (HCOO Cs ) for applications such as oil drilling . To supply
672-511: A few tens to exist. Hawaii , Réunion , Yellowstone , Galápagos , and Iceland are some of the most active volcanic regions to which the hypothesis is applied. The plumes imaged to date vary widely in width and other characteristics, and are tilted, being not the simple, relatively narrow and purely thermal plumes many expected. Only one, (Yellowstone) has as yet been consistently modelled and imaged from deep mantle to surface. Most hotspot volcanoes are basaltic (e.g., Hawaii , Tahiti ). As
768-424: A heavy element, caesium provides good stopping power with better detection. Caesium compounds may provide a faster response (CsF) and be less hygroscopic (CsI). Caesium vapour is used in many common magnetometers . The element is used as an internal standard in spectrophotometry . Like other alkali metals , caesium has a great affinity for oxygen and is used as a " getter " in vacuum tubes . Other uses of
864-431: A mixture of soluble chlorides is produced, and the insoluble chloride double salts of caesium are precipitated as caesium antimony chloride ( Cs 4 SbCl 7 ), caesium iodine chloride ( Cs 2 ICl ), or caesium hexachlorocerate ( Cs 2 (CeCl 6 ) ). After separation, the pure precipitated double salt is decomposed, and pure CsCl is precipitated by evaporating the water. The sulfuric acid method yields
960-437: A narrow arc some distance from the trench. The distance from the trench to the volcanic arc is greater for slabs subducting at a shallower angle, and this suggests that magma generation takes place when the slab reached a critical depth for the breakdown of an abundant hydrous mineral. This would produce an ascending "hydrous curtain" that accounts for focused volcanism along the volcanic arc. However, some models suggest that water
1056-500: A result, they are less explosive than subduction zone volcanoes, in which water is trapped under the overriding plate. Where hotspots occur in continental regions , basaltic magma rises through the continental crust, which melts to form rhyolites . These rhyolites can form violent eruptions. For example, the Yellowstone Caldera was formed by some of the most powerful volcanic explosions in geologic history. However, when
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#17328732865441152-600: A shell be bent downwards by an angle of θ, without tearing or wrinkling, only on a circle whose radius is θ/2. This means that arcs where the subducting slab descends at a shallower angle will be more tightly curved. Prominent arcs whose slabs subduct at about 45 degrees, such as the Kuril Islands , the Aleutian Islands , and the Sunda Arc , have a radius of about 20 to 22 degrees. Volcanic arcs are divided into those in which
1248-448: A subduction zone. The active front of a volcanic arc is the belt where volcanism develops at a given time. Active fronts may move over time (millions of years), changing their distance from the oceanic trench as well as their width. A volcanic arc is part of an arc-trench complex , which is the part of a subduction zone that is visible at the Earth's surface. A subduction zone is where
1344-419: A very long half-life of about 2.3 million years, the longest of all radioactive isotopes of caesium. Cs and Cs have half-lives of 30 and two years, respectively. Cs decomposes to a short-lived Ba by beta decay , and then to nonradioactive barium, while Cs transforms into Ba directly. The isotopes with mass numbers of 129, 131, 132 and 136, have half-lives between a day and two weeks, while most of
1440-577: Is hygroscopic and strongly basic . It rapidly etches the surface of semiconductors such as silicon . CsOH has been previously regarded by chemists as the "strongest base", reflecting the relatively weak attraction between the large Cs ion and OH ; it is indeed the strongest Arrhenius base ; however, a number of compounds such as n -butyllithium , sodium amide , sodium hydride , caesium hydride , etc., which cannot be dissolved in water as reacting violently with it but rather only used in some anhydrous polar aprotic solvents , are far more basic on
1536-456: Is a chemical element ; it has symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F; 301.6 K), which makes it one of only five elemental metals that are liquid at or near room temperature . Caesium has physical and chemical properties similar to those of rubidium and potassium . It is pyrophoric and reacts with water even at −116 °C (−177 °F). It
1632-649: Is also larger and less "hard" than those of the lighter alkali metals . Most caesium compounds contain the element as the cation Cs , which binds ionically to a wide variety of anions . One noteworthy exception is the caeside anion ( Cs ), and others are the several suboxides (see section on oxides below). More recently, caesium is predicted to behave as a p-block element and capable of forming higher fluorides with higher oxidation states (i.e., CsF n with n > 1) under high pressure. This prediction needs to be validated by further experiments. Salts of Cs are usually colourless unless
1728-497: Is also liquid at room temperature (melting at −7.2 °C [19.0 °F]), but it is a halogen and not a metal. Mercury is the only stable elemental metal with a known melting point lower than caesium. In addition, the metal has a rather low boiling point , 641 °C (1,186 °F), the lowest of all stable metals other than mercury. Copernicium and flerovium have been predicted to have lower boiling points than mercury and caesium, but they are extremely radioactive and it
1824-510: Is also used as a source of positive ions in secondary ion mass spectrometry (SIMS). Since 1967, the International System of Measurements has based the primary unit of time, the second, on the properties of caesium. The International System of Units (SI) defines the second as the duration of 9,192,631,770 cycles at the microwave frequency of the spectral line corresponding to the transition between two hyperfine energy levels of
1920-558: Is classified as a hazardous material . It is stored and shipped in dry, saturated hydrocarbons such as mineral oil . It can be handled only under inert gas , such as argon . However, a caesium-water explosion is often less powerful than a sodium -water explosion with a similar amount of sodium. This is because caesium explodes instantly upon contact with water, leaving little time for hydrogen to accumulate. Caesium can be stored in vacuum-sealed borosilicate glass ampoules . In quantities of more than about 100 grams (3.5 oz), caesium
2016-406: Is continuously released from the slab from shallow depths down to 70 to 300 kilometers (43 to 186 mi), and much of the water released at shallow depths produces serpentinization of the overlying mantle wedge. According to one model, only about 18 to 37 percent of the water content is released at sufficient depth to produce arc magmatism. The volcanic arc is then interpreted as the depth at which
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#17328732865442112-434: Is crushed, hand-sorted, but not usually concentrated, and then ground. Caesium is then extracted from pollucite primarily by three methods: acid digestion, alkaline decomposition, and direct reduction. In the acid digestion, the silicate pollucite rock is dissolved with strong acids, such as hydrochloric (HCl), sulfuric ( H 2 SO 4 ), hydrobromic (HBr), or hydrofluoric (HF) acids. With hydrochloric acid,
2208-430: Is formed. Arc volcanism takes place where the slab descends out from under the cool shallow corner, allowing magma to be generated and rise through warmer, less stiff mantle rock. Magma may be generated over a broad area but become focused into a narrow volcanic arc by a permeability barrier at the base of the overriding plate. Numerical simulations suggest that crystallization of rising magma creates this barrier, causing
2304-430: Is found in few minerals. Percentage amounts of caesium may be found in beryl ( Be 3 Al 2 (SiO 3 ) 6 ) and avogadrite ( (K,Cs)BF 4 ), up to 15 wt% Cs 2 O in the closely related mineral pezzottaite ( Cs(Be 2 Li)Al 2 Si 6 O 18 ), up to 8.4 wt% Cs 2 O in the rare mineral londonite ( (Cs,K)Al 4 Be 4 (B,Be) 12 O 28 ), and less in
2400-413: Is lost from the subducted plate when the temperature and pressure become sufficient to break down these minerals and release their water content. The water rises into the wedge of mantle overlying the slab and lowers the melting point of mantle rock to the point where magma is generated. While there is wide agreement on the general mechanism, research continues on the explanation for focused volcanism along
2496-543: Is low in volcanic arc rocks. Because volcanic rock is easily weathered and eroded , older volcanic arcs are seen as plutonic rocks , the rocks that formed underneath the arc (e.g. the Sierra Nevada batholith ), or in the sedimentary record as lithic sandstones . Paired metamorphic belts , in which a belt of high-temperature, low-pressure metamorphism is located parallel to a belt of low-temperature, high-pressure metamorphism, preserve an ancient arc-trench complex in which
2592-472: Is mined for its petalite, but it also contains a significant amount of pollucite. Another notable source of pollucite is in the Karibib Desert , Namibia . At the present rate of world mine production of 5 to 10 metric tons per year, reserves will last for thousands of years. Mining and refining pollucite ore is a selective process and is conducted on a smaller scale than for most other metals. The ore
2688-429: Is not certain if they are metals. Caesium forms alloys with the other alkali metals, gold , and mercury ( amalgams ). At temperatures below 650 °C (1,202 °F), it does not alloy with cobalt , iron , molybdenum , nickel , platinum , tantalum , or tungsten . It forms well-defined intermetallic compounds with antimony , gallium , indium , and thorium , which are photosensitive . It mixes with all
2784-598: Is not linked to a constructive or destructive plate margin, the concept of a hotspot has been used to explain its origin. A review article by Courtillot et al. listing possible hotspots makes a distinction between primary hotspots coming from deep within the mantle and secondary hotspots derived from mantle plumes. The primary hotspots originate from the core/mantle boundary and create large volcanic provinces with linear tracks (Easter Island, Iceland, Hawaii, Afar, Louisville, Reunion, and Tristan confirmed; Galapagos, Kerguelen and Marquersas likely). The secondary hotspots originate at
2880-477: Is now closely linked to the mantle plume hypothesis. The detailed compositional studies now possible on hotspot basalts have allowed linkage of samples over the wider areas often implicate in the later hypothesis, and it's seismic imaging developments. Hotspot volcanoes are considered to have a fundamentally different origin from island arc volcanoes. The latter form over subduction zones, at converging plate boundaries. When one oceanic plate meets another,
2976-549: Is now used to explain such observations. In 2020, Wei et al. used seismic tomography to detect the oceanic plateau, formed about 100 million years ago by the hypothesized mantle plume head of the Hawaii-Emperor seamount chain, now subducted to a depth of 800 km under eastern Siberia. Download coordinates as: Caesium Caesium ( IUPAC spelling; also spelled cesium in American English )
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3072-481: Is one of the " incompatible elements ". During magma crystallization , caesium is concentrated in the liquid phase and crystallizes last. Therefore, the largest deposits of caesium are zone pegmatite ore bodies formed by this enrichment process. Because caesium does not substitute for potassium as readily as rubidium does, the alkali evaporite minerals sylvite (KCl) and carnallite ( KMgCl 3 ·6H 2 O ) may contain only 0.002% caesium. Consequently, caesium
3168-614: Is particularly characteristic of volcanic arcs, though it sometimes also occurs in regions of crustal extension. In the rock record, volcanic arcs can be recognized from their thick sequences of volcaniclastic rock (formed by explosive volcanism) interbedded with greywackes and mudstones and by their calc-alkaline composition. In more ancient rocks that have experienced metamorphism and alteration of their composition ( metasomatism ), calc-alkaline rocks can be distinguished by their content of trace elements that are little affected by alteration, such as chromium or titanium , whose content
3264-448: Is reduced in most reactors because the predecessor, Xe , is a potent neutron poison and frequently transmutes to stable Xe before it can decay to Cs. The beta decay from Cs to Ba results in gamma radiation as the Ba relaxes to ground state Ba, with the emitted photons having an energy of 0.6617 MeV. Cs and Sr are the principal medium-lived products of nuclear fission , and
3360-545: Is shipped in hermetically sealed, stainless steel containers. The chemistry of caesium is similar to that of other alkali metals, in particular rubidium , the element above caesium in the periodic table. As expected for an alkali metal, the only common oxidation state is +1. It differs from this value in caesides, which contain the Cs anion and thus have caesium in the −1 oxidation state. Under conditions of extreme pressure (greater than 30 GPa ), theoretical studies indicate that
3456-626: Is the Tanco Mine at Bernic Lake in Manitoba , Canada, estimated to contain 350,000 metric tons of pollucite ore, representing more than two-thirds of the world's reserve base. Although the stoichiometric content of caesium in pollucite is 42.6%, pure pollucite samples from this deposit contain only about 34% caesium, while the average content is 24 wt%. Commercial pollucite contains more than 19% caesium. The Bikita pegmatite deposit in Zimbabwe
3552-547: Is the least electronegative stable element, with a value of 0.79 on the Pauling scale . It has only one stable isotope , caesium-133 . Caesium is mined mostly from pollucite . Caesium-137 , a fission product , is extracted from waste produced by nuclear reactors . It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometres . The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by
3648-534: Is the primary standard for standards-compliant time and frequency measurements. Caesium clocks regulate the timing of cell phone networks and the Internet. The second, symbol s , is the SI unit of time. The BIPM restated its definition at its 26th conference in 2018: "[The second] is defined by taking the fixed numerical value of the caesium frequency Δ ν Cs , the unperturbed ground-state hyperfine transition frequency of
3744-728: Is used in photoelectric cells because caesium-based cathodes, such as the intermetallic compound K 2 CsSb , have a low threshold voltage for emission of electrons . The range of photoemissive devices using caesium include optical character recognition devices, photomultiplier tubes , and video camera tubes . Nevertheless, germanium , rubidium, selenium, silicon, tellurium, and several other elements can be substituted for caesium in photosensitive materials. Caesium iodide (CsI), bromide (CsBr) and fluoride (CsF) crystals are employed for scintillators in scintillation counters widely used in mineral exploration and particle physics research to detect gamma and X-ray radiation. Being
3840-619: The National Physical Laboratory in the UK. Caesium clocks have improved over the past half-century and are regarded as "the most accurate realization of a unit that mankind has yet achieved." These clocks measure frequency with an error of 2 to 3 parts in 10 , which corresponds to an accuracy of 2 nanoseconds per day, or one second in 1.4 million years. The latest versions are more accurate than 1 part in 10 , about 1 second in 20 million years. The caesium standard
3936-403: The beta decay of originally more neutron-rich fission products, passing through various isotopes of iodine and xenon . Because iodine and xenon are volatile and can diffuse through nuclear fuel or air, radioactive caesium is often created far from the original site of fission. With nuclear weapons testing in the 1950s through the 1980s, Cs was released into the atmosphere and returned to
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4032-400: The electrical conductivity . Caesium was not recognized as a high-performance industrial metal until the 1950s. Applications for nonradioactive caesium included photoelectric cells , photomultiplier tubes, optical components of infrared spectrophotometers , catalysts for several organic reactions, crystals for scintillation counters , and in magnetohydrodynamic power generators . Caesium
4128-415: The extractive oil industry . Aqueous solutions of caesium formate (HCOO Cs )—made by reacting caesium hydroxide with formic acid —were developed in the mid-1990s for use as oil well drilling and completion fluids . The function of a drilling fluid is to lubricate drill bits, to bring rock cuttings to the surface, and to maintain pressure on the formation during drilling of the well. Completion fluids assist
4224-403: The ground state of caesium-133 . The 13th General Conference on Weights and Measures of 1967 defined a second as: "the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of caesium-133 atoms in their ground state undisturbed by external fields". The largest present-day use of nonradioactive caesium is in caesium formate drilling fluids for
4320-496: The ozonide CsO 3 , several brightly coloured suboxides have also been studied. These include Cs 7 O , Cs 4 O , Cs 11 O 3 , Cs 3 O (dark-green ), CsO, Cs 3 O 2 , as well as Cs 7 O 2 . The latter may be heated in a vacuum to generate Cs 2 O . Binary compounds with sulfur , selenium , and tellurium also exist. Caesium has 41 known isotopes , ranging in mass number (i.e. number of nucleons in
4416-404: The superoxide CsO 2 is the main product. The "normal" caesium oxide ( Cs 2 O ) forms yellow-orange hexagonal crystals, and is the only oxide of the anti- CdCl 2 type. It vaporizes at 250 °C (482 °F), and decomposes to caesium metal and the peroxide Cs 2 O 2 at temperatures above 400 °C (752 °F). In addition to the superoxide and
4512-412: The 1990s, the largest application of the element has been as caesium formate for drilling fluids , but it has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology. Nonradioactive caesium compounds are only mildly toxic , but
4608-701: The North Pacific, with the Aleutian Arc consisting of the Aleutian Islands and their extension the Aleutian Range on the Alaska Peninsula , and the Kuril–Kamchatka Arc comprising the Kuril Islands and southern Kamchatka Peninsula . Hotspot (geology) In geology , hotspots (or hot spots ) are volcanic locales thought to be fed by underlying mantle that is anomalously hot compared with
4704-554: The anion itself is coloured. Many of the simple salts are hygroscopic , but less so than the corresponding salts of lighter alkali metals. The phosphate , acetate , carbonate , halides , oxide , nitrate , and sulfate salts are water-soluble. Its double salts are often less soluble, and the low solubility of caesium aluminium sulfate is exploited in refining Cs from ores. The double salts with antimony (such as CsSbCl 4 ), bismuth , cadmium , copper , iron , and lead are also poorly soluble . Caesium hydroxide (CsOH)
4800-582: The basis of the Brønsted–Lowry acid–base theory . A stoichiometric mixture of caesium and gold will react to form yellow caesium auride (Cs Au ) upon heating. The auride anion here behaves as a pseudohalogen . The compound reacts violently with water, yielding caesium hydroxide , metallic gold, and hydrogen gas; in liquid ammonia it can be reacted with a caesium-specific ion exchange resin to produce tetramethylammonium auride . The analogous platinum compound, red caesium platinide ( Cs 2 Pt ), contains
4896-447: The caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz , which is equal to s ." Caesium vapour thermionic generators are low-power devices that convert heat energy to electrical energy. In the two-electrode vacuum tube converter, caesium neutralizes the space charge near the cathode and enhances the current flow. Caesium is also important for its photoemissive properties, converting light to electron flow. It
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#17328732865444992-466: The components of many other heavy liquids, caesium formate is relatively environment-friendly. Caesium formate brine can be blended with potassium and sodium formates to decrease the density of the fluids to that of water (1.0 g/cm , or 8.3 pounds per gallon). Furthermore, it is biodegradable and may be recycled, which is important in view of its high cost (about $ 4,000 per barrel in 2001). Alkali formates are safe to handle and do not damage
5088-482: The core–mantle boundary. The alternative plate theory is that the mantle source beneath a hotspot is not anomalously hot, rather the crust above is unusually weak or thin, so that lithospheric extension permits the passive rising of melt from shallow depths. The origins of the concept of hotspots lie in the work of J. Tuzo Wilson , who postulated in 1963 that the formation of the Hawaiian Islands resulted from
5184-688: The crust and magmatic underplating contribute to thickening of the crust. Volcanic arcs are characterized by explosive eruption of calc-alkaline magma, though young arcs sometimes erupt tholeiitic magma and a few arcs erupt alkaline magma. Calc-alkaline magma can be distinguished from tholeiitic magma, typical of mid-ocean ridges , by its higher aluminium and lower iron content and by its high content of large-ion lithophile elements, such as potassium , rubidium , caesium , strontium , or barium , relative to high-field-strength elements, such as zirconium , niobium , hafnium , rare-earth elements (REE), thorium , uranium , or tantalum . Andesite
5280-498: The cube, while the caesium atoms lie in the holes in the centre of the cubes. This structure is shared with CsBr and CsI , and many other compounds that do not contain Cs. In contrast, most other alkaline halides have the sodium chloride (NaCl) structure. The CsCl structure is preferred because Cs has an ionic radius of 174 pm and Cl 181 pm. More so than the other alkali metals, caesium forms numerous binary compounds with oxygen . When caesium burns in air,
5376-406: The currently accepted one of 132.9). They tried to generate elemental caesium by electrolysis of molten caesium chloride, but instead of a metal, they obtained a blue homogeneous substance which "neither under the naked eye nor under the microscope showed the slightest trace of metallic substance"; as a result, they assigned it as a subchloride ( Cs 2 Cl ). In reality, the product was probably
5472-528: The decreasing frequency of light required to excite electrons of the alkali metals as the group is descended. For lithium through rubidium this frequency is in the ultraviolet, but for caesium it enters the blue–violet end of the spectrum; in other words, the plasmonic frequency of the alkali metals becomes lower from lithium to caesium. Thus caesium transmits and partially absorbs violet light preferentially while other colours (having lower frequency) are reflected; hence it appears yellowish. Its compounds burn with
5568-401: The degree of melting becomes great enough to allow the magma to separate from its source rock. It is now known that the subducting slab may be located anywhere from 60 to 173 kilometers (37 to 107 mi) below the volcanic arc, rather than a single characteristic depth of around 120 kilometers (75 mi), which requires more elaborate models of arc magmatism. For example, water released from
5664-408: The denser plate is forced downward into a deep ocean trench. This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise. It is this that fuels a chain of volcanoes, such as the Aleutian Islands , near Alaska . The joint mantle plume /hotspot hypothesis originally envisaged
5760-450: The developing market, Cabot Corporation built a production plant in 1997 at the Tanco mine near Bernic Lake in Manitoba , with a capacity of 12,000 barrels (1,900 m ) per year of caesium formate solution. The primary smaller-scale commercial compounds of caesium are caesium chloride and nitrate . Alternatively, caesium metal may be obtained from the purified compounds derived from
5856-441: The emplacement of control hardware after drilling but prior to production by maintaining the pressure. The high density of the caesium formate brine (up to 2.3 g/cm , or 19.2 pounds per gallon), coupled with the relatively benign nature of most caesium compounds, reduces the requirement for toxic high-density suspended solids in the drilling fluid—a significant technological, engineering and environmental advantage. Unlike
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#17328732865445952-504: The feeder structures to be fixed relative to one another, with the continents and seafloor drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are developed on the surface. Examples are Yellowstone , which lies at the end of a chain of extinct calderas, which become progressively older to the west. Another example is the Hawaiian archipelago, where islands become progressively older and more deeply eroded to
6048-432: The hexachloroplatinate with hydrogen , caesium and rubidium were separated by the difference in solubility of their carbonates in alcohol. The process yielded 9.2 grams (0.32 oz) of rubidium chloride and 7.3 grams (0.26 oz) of caesium chloride from the initial 44,000 litres of mineral water. From the caesium chloride, the two scientists estimated the atomic weight of the new element at 123.35 (compared to
6144-496: The high-temperature, low-pressure belt corresponds to the volcanic arc. In a subduction zone , loss of water from the subducted slab induces partial melting of the overriding mantle and generates low-density, calc-alkaline magma that buoyantly rises to intrude and be extruded through the lithosphere of the overriding plate. Most of the water carried downwards by the slab is contained in hydrous (water-bearing) minerals, such as mica , amphibole , or serpentinite minerals. Water
6240-452: The inner 5p electrons could form chemical bonds, where caesium would behave as the seventh 5p element, suggesting that higher caesium fluorides with caesium in oxidation states from +2 to +6 could exist under such conditions. Some slight differences arise from the fact that it has a higher atomic mass and is more electropositive than other (nonradioactive) alkali metals. Caesium is the most electropositive chemical element. The caesium ion
6336-508: The insoluble double salt directly as caesium alum ( CsAl(SO 4 ) 2 ·12H 2 O ). The aluminium sulfate component is converted to insoluble aluminium oxide by roasting the alum with carbon , and the resulting product is leached with water to yield a Cs 2 SO 4 solution. Roasting pollucite with calcium carbonate and calcium chloride yields insoluble calcium silicates and soluble caesium chloride. Leaching with water or dilute ammonia ( NH 4 OH ) yields
6432-405: The lowest and highest electronegativities , respectively, among all the known elements. Caesium chloride (CsCl) crystallizes in the simple cubic crystal system . Also called the "caesium chloride structure", this structural motif is composed of a primitive cubic lattice with a two-atom basis, each with an eightfold coordination ; the chloride atoms lie upon the lattice points at the edges of
6528-485: The more widespread rhodizite . The only economically important ore for caesium is pollucite Cs(AlSi 2 O 6 ) , which is found in a few places around the world in zoned pegmatites, associated with the more commercially important lithium minerals, lepidolite and petalite . Within the pegmatites, the large grain size and the strong separation of the minerals results in high-grade ore for mining. The world's most significant and richest known source of caesium
6624-405: The newly developed method of flame spectroscopy . The first small-scale applications for caesium were as a " getter " in vacuum tubes and in photoelectric cells . Caesium is widely used in highly accurate atomic clocks . In 1967, the International System of Units began using a specific hyperfine transition of neutral caesium-133 atoms to define the basic unit of time, the second . Since
6720-534: The northwest. Geologists have tried to use hotspot volcanic chains to track the movement of the Earth's tectonic plates. This effort has been vexed by the lack of very long chains, by the fact that many are not time-progressive (e.g. the Galápagos ) and by the fact that hotspots do not appear to be fixed relative to one another (e.g. Hawaii and Iceland ). That mantle plumes are much more complex than originally hypothesised and move independently of each other and plates
6816-520: The nucleus) from 112 to 152. Several of these are synthesized from lighter elements by the slow neutron capture process ( S-process ) inside old stars and by the R-process in supernova explosions. The only stable caesium isotope is Cs, with 78 neutrons . Although it has a large nuclear spin ( 7 / 2 +), nuclear magnetic resonance studies can use this isotope at a resonating frequency of 11.7 MHz . The radioactive Cs has
6912-776: The ore. Caesium chloride and the other caesium halides can be reduced at 700 to 800 °C (1,292 to 1,472 °F) with calcium or barium , and caesium metal distilled from the result. In the same way, the aluminate, carbonate, or hydroxide may be reduced by magnesium . The metal can also be isolated by electrolysis of fused caesium cyanide (CsCN). Exceptionally pure and gas-free caesium can be produced by 390 °C (734 °F) thermal decomposition of caesium azide CsN 3 , which can be produced from aqueous caesium sulfate and barium azide . In vacuum applications, caesium dichromate can be reacted with zirconium to produce pure caesium metal without other gaseous products. The price of 99.8% pure caesium (metal basis) in 2009
7008-412: The other alkali metals (except lithium); the alloy with a molar distribution of 41% caesium, 47% potassium , and 12% sodium has the lowest melting point of any known metal alloy, at −78 °C (−108 °F). A few amalgams have been studied: CsHg 2 is black with a purple metallic lustre , while CsHg is golden-coloured, also with a metallic lustre. The golden colour of caesium comes from
7104-410: The other isotopes have half-lives from a few seconds to fractions of a second. At least 21 metastable nuclear isomers exist. Other than Cs (with a half-life of just under 3 hours), all are very unstable and decay with half-lives of a few minutes or less. The isotope Cs is one of the long-lived fission products of uranium produced in nuclear reactors . However, this fission product yield
7200-478: The overriding plate coincides with a deep and narrow oceanic trench . This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur within the subducting slab with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Wadati–Benioff zones . The volcanic arc forms on
7296-415: The overriding plate is continental (Andean-type arcs) and those in which the overriding plate is oceanic (intraoceanic or primitive arcs). The crust beneath the arc is up to twice as thick as average continental or oceanic crust: The crust under Andean-type arcs is up to 80 kilometers (50 mi) thick, while the crust under intraoceanic arcs is 20 to 35 kilometers (12 to 22 mi) thick. Both shortening of
7392-431: The overriding plate over the point where the subducting plate reaches a depth of roughly 120 kilometres (75 mi) and is a zone of volcanic activity between 50 and 200 kilometers (31 and 124 mi) in width. The shape of a volcanic arc is typically convex towards the subducting plate. This is a consequence of the spherical geometry of the Earth. The subducting plate behaves like a flexible thin spherical shell, and such
7488-478: The platinide ion that behaves as a pseudo chalcogen . Like all metal cations, Cs forms complexes with Lewis bases in solution. Because of its large size, Cs usually adopts coordination numbers greater than 6, the number typical for the smaller alkali metal cations. This difference is apparent in the 8-coordination of CsCl. This high coordination number and softness (tendency to form covalent bonds) are properties exploited in separating Cs from other cations in
7584-529: The presence of trace amounts of oxygen . When in the presence of mineral oil (where it is best kept during transport), it loses its metallic lustre and takes on a duller, grey appearance. It has a melting point of 28.5 °C (83.3 °F), making it one of the few elemental metals that are liquid near room temperature . The others are rubidium (39 °C [102 °F]), francium (estimated at 27 °C [81 °F]), mercury (−39 °C [−38 °F]), and gallium (30 °C [86 °F]); bromine
7680-507: The prime sources of radioactivity from spent nuclear fuel after several years of cooling, lasting several hundred years. Those two isotopes are the largest source of residual radioactivity in the area of the Chernobyl disaster . Because of the low capture rate, disposing of Cs through neutron capture is not feasible and the only current solution is to allow it to decay over time. Almost all caesium produced from nuclear fission comes from
7776-414: The problems with the chloride. Historically, the most important use for caesium has been in research and development, primarily in chemical and electrical fields. Very few applications existed for caesium until the 1920s, when it came into use in radio vacuum tubes , where it had two functions; as a getter , it removed excess oxygen after manufacture, and as a coating on the heated cathode , it increased
7872-425: The producing formation or downhole metals as corrosive alternative, high-density brines (such as zinc bromide ZnBr 2 solutions) sometimes do; they also require less cleanup and reduce disposal costs. Caesium-based atomic clocks use the electromagnetic transitions in the hyperfine structure of caesium-133 atoms as a reference point. The first accurate caesium clock was built by Louis Essen in 1955 at
7968-508: The pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, and the radioisotopes present a significant health and environmental hazard. Caesium is the spelling recommended by the International Union of Pure and Applied Chemistry (IUPAC). The American Chemical Society (ACS) has used the spelling cesium since 1921, following Webster's New International Dictionary . The element
8064-409: The released water lowers the melting point of the overlying mantle wedge enough for melting. The location of the volcanic arc may be determined by the presence of a cool shallow corner at the tip of the mantle wedge, where the mantle rock is cooled by both the overlying plate and the slab. Not only does the cool shallow corner suppress melting, but its high stiffness hinders the ascent of any magma that
8160-679: The remaining magma to pool in a narrow band at the apex of the barrier. This narrow band corresponds to the overlying volcanic arc. Two classic examples of oceanic island arcs are the Mariana Islands in the western Pacific Ocean and the Lesser Antilles in the western Atlantic Ocean. The Cascade Volcanic Arc in western North America and the Andes along the western edge of South America are examples of continental volcanic arcs. The best examples of volcanic arcs with both sets of characteristics are in
8256-438: The remediation of nuclear wastes, where Cs must be separated from large amounts of nonradioactive K . Caesium fluoride (CsF) is a hygroscopic white solid that is widely used in organofluorine chemistry as a source of fluoride anions. Caesium fluoride has the halite structure, which means that the Cs and F pack in a cubic closest packed array as do Na and Cl in sodium chloride . Notably, caesium and fluorine have
8352-516: The rhyolite is completely erupted, it may be followed by eruptions of basaltic magma rising through the same lithospheric fissures (cracks in the lithosphere). An example of this activity is the Ilgachuz Range in British Columbia, which was created by an early complex series of trachyte and rhyolite eruptions, and late extrusion of a sequence of basaltic lava flows. The hotspot hypothesis
8448-411: The slab at moderate depths might react with amphibole minerals in the lower part of the mantle wedge to produce water-rich chlorite . This chlorite-rich mantle rock is then dragged downwards by the subducting slab, and eventually breaks down to become the source of arc magmatism. The location of the arc depends on the angle and rate of subduction, which determine where hydrous minerals break down and where
8544-442: The slow movement of a tectonic plate across a hot region beneath the surface. It was later postulated that hotspots are fed by streams of hot mantle rising from the Earth's core–mantle boundary in a structure called a mantle plume . Whether or not such mantle plumes exist has been the subject of a major controversy in Earth science, but seismic images consistent with evolving theory now exist. At any place where volcanism
8640-495: The solution. After conversion to the nitrates and extraction with ethanol , a sodium-free mixture was obtained. From this mixture, the lithium was precipitated by ammonium carbonate . Potassium, rubidium, and caesium form insoluble salts with chloroplatinic acid , but these salts show a slight difference in solubility in hot water, and the less-soluble caesium and rubidium hexachloroplatinate ( (Cs,Rb) 2 PtCl 6 ) were obtained by fractional crystallization . After reduction of
8736-410: The southeast end of the chain over the hotspot. Volcanic arcs do not generally exhibit such a simple age-pattern. There are two types of volcanic arcs: In some situations, a single subduction zone may show both aspects along its length, as part of a plate subducts beneath a continent and part beneath adjacent oceanic crust. The Aleutian Islands and adjoining Alaskan Peninsula are an example of such
8832-465: The surface of the earth as a component of radioactive fallout . It is a ready marker of the movement of soil and sediment from those times. Caesium is a relatively rare element, estimated to average 3 parts per million in the Earth's crust . It is the 45th most abundant element and 36th among the metals. Caesium is 30 times less abundant than rubidium , with which it is closely associated, chemically. Due to its large ionic radius , caesium
8928-470: The surrounding mantle. Examples include the Hawaii , Iceland , and Yellowstone hotspots . A hotspot's position on the Earth's surface is independent of tectonic plate boundaries , and so hotspots may create a chain of volcanoes as the plates move above them. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from
9024-526: The upper/lower mantle boundary, and do not form large volcanic provinces, but island chains (Samoa, Tahiti, Cook, Pitcairn, Caroline, MacDonald confirmed, with up to 20 or so more possible). Other potential hotspots are the result of shallow mantle material surfacing in areas of lithospheric break-up caused by tension and are thus a very different type of volcanism. Estimates for the number of hotspots postulated to be fed by mantle plumes have ranged from about 20 to several thousand, with most geologists considering
9120-448: Was about $ 10 per gram ($ 280/oz), but the compounds are significantly cheaper. In 1860, Robert Bunsen and Gustav Kirchhoff discovered caesium in the mineral water from Dürkheim , Germany. Because of the bright blue lines in the emission spectrum , they derived the name from the Latin word caesius , meaning ' bluish grey ' . Caesium was the first element to be discovered with
9216-490: Was named after the Latin word caesius , meaning "bluish grey". In medieval and early modern writings caesius was spelled with the ligature æ as cæsius ; hence, an alternative but now old-fashioned orthography is cæsium . More spelling explanation at ae/oe vs e . Of all elements that are solid at room temperature, caesium is the softest: it has a hardness of 0.2 Mohs . It is a very ductile , pale metal, which darkens in
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