A cave or cavern is a natural void in the ground a space large enough for a human to enter. Caves form by the weathering of rock and extend deep underground; the word cave can refer to much smaller openings such as sea caves, rock shelters, grottos, though speaking a cave is exogene, meaning it is deeper than its opening is wide, a rock shelter is endogene. Speleology is the science of study of all aspects of caves and the cave environment. Visiting or exploring caves for recreation may be called caving, potholing, or spelunking; the formation and development of caves is known as speleogenesis. Caves can range in size, are formed by various geological processes; these may involve a combination of chemical processes, erosion by water, tectonic forces, microorganisms and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, to determine the timescale of the geological events which formed and shaped present-day caves, it is estimated that a cave cannot exceed 3,000 metres in depth due to the pressure of overlying rocks.
For karst caves the maximum depth is determined on the basis of the lower limit of karst forming processes, coinciding with the base of the soluble carbonate rocks. Most caves are formed in limestone by dissolution. Caves can be classified in various other ways as well, including a contrast between active and relict: active caves have water flowing through them. Types of active caves include inflow caves, outflow caves, through caves. Solutional caves or karst caves are the most occurring caves; such caves form in rock, soluble. Rock is dissolved by natural acid in groundwater that seeps through bedding planes, faults and comparable features. Over time cracks enlarge to become caves and cave systems; the largest and most abundant solutional caves are located in limestone. Limestone dissolves under the action of rainwater and groundwater charged with H2CO3 and occurring organic acids; the dissolution process produces a distinctive landform known as karst, characterized by sinkholes and underground drainage.
Limestone caves are adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalagmites, soda straws and columns; these secondary mineral deposits in caves are called speleothems. The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded. Lechuguilla Cave in New Mexico and nearby Carlsbad Cavern are now believed to be examples of another type of solutional cave, they were formed by H2S gas rising from below. This gas mixes with groundwater and forms H2SO4; the acid dissolves the limestone from below, rather than from above, by acidic water percolating from the surface. Caves formed at the same time. Lava tubes are the most common primary caves; as lava flows downhill, its surface solidifies. Hot liquid lava continues to flow under that crust, if most of it flows out, a hollow tube remains; such caves can be found in the Canary Islands, Jeju-do, the basaltic plains of Eastern Idaho, in other places.
Kazumura Cave near Hilo, Hawaii is a remarkably deep lava tube. Lava caves are not limited to lava tubes. Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, blisters, among others. Sea caves are found along coasts around the world. A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs; these weaknesses are faults, but they may be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of uplift. Elsewhere, in places such as Thailand's Phang Nga Bay, solutional caves have been flooded by the sea and are now subject to littoral erosion. Sea caves are around 5 to 50 metres in length, but may exceed 300 metres. Corrasional or erosional caves are those that form by erosion by flowing streams carrying rocks and other sediments; these can form in any type including hard rocks such as granite. There must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the aeolian cave, carved by wind-born sediments.
Many caves formed by solutional processes undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them. Glacier caves are formed by flowing water within and under glaciers; the cavities are influenced by the slow flow of the ice, which tends to collapse the caves again. Glacier caves are sometimes misidentified as "ice caves", though this latter term is properly reserved for bedrock caves that contain year-round ice formations. Fracture caves are formed when layers of more soluble minerals, such as gypsum, dissolve out from between layers of less soluble rock; these rocks fracture and collapse in blocks of stone. Talus caves are formed by the openings among large boulders that have fallen down into a random heap at the bases of cliffs; these unstable deposits are called talus or scree, may be subject to frequent rockfalls and landslides. Anchialine ca
Hard water is water that has high mineral content. Hard water is formed when water percolates through deposits of limestone and chalk which are made up of calcium and magnesium carbonates. Hard drinking water may have moderate health benefits, but can pose critical problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling towers, other equipment that handles water. In domestic settings, hard water is indicated by a lack of foam formation when soap is agitated in water, by the formation of limescale in kettles and water heaters. Wherever water hardness is a concern, water softening is used to reduce hard water's adverse effects. Water's hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are positively charged metal complexes with a charge greater than 1+; the cations have the charge of 2+. Common cations found in hard water include Ca2+ and Mg2+; these ions enter a water supply by leaching from minerals within an aquifer.
Common calcium-containing minerals are gypsum. A common magnesium mineral is dolomite. Rainwater and distilled water are soft; the following equilibrium reaction describes the dissolving and formation of calcium carbonate and calcium bicarbonate: CaCO3 + CO2 + H2O ⇋ Ca2+ + 2HCO3− The reaction can go in either direction. Rain containing dissolved carbon dioxide can react with calcium carbonate and carry calcium ions away with it; the calcium carbonate may be re-deposited as calcite as the carbon dioxide is lost to atmosphere, sometimes forming stalactites and stalagmites. Calcium and magnesium ions can sometimes be removed by water softeners. Temporary hardness is a type of water hardness caused by the presence of dissolved bicarbonate minerals; when dissolved, these minerals yield calcium and magnesium cations and carbonate and bicarbonate anions. The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulfate and chloride compounds, this "temporary" hardness can be reduced either by boiling the water, or by the addition of lime through the process of lime softening.
Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water, softer upon cooling. Permanent hardness is hardness; when this is the case, it is caused by the presence of calcium sulfate/calcium chloride and/or magnesium sulfate/magnesium chloride in the water, which do not precipitate out as the temperature increases. Ions causing permanent hardness of water can be removed using a water softener, or ion exchange column. Total Permanent Hardness = Permanent Calcium Hardness + Permanent Magnesium Hardness With hard water, soap solutions form a white precipitate instead of producing lather, because the 2+ ions destroy the surfactant properties of the soap by forming a solid precipitate. A major component of such scum is calcium stearate, which arises from sodium stearate, the main component of soap: 2 C17H35COO− + Ca2+ → 2Ca Hardness can thus be defined as the soap-consuming capacity of a water sample, or the capacity of precipitation of soap as a characteristic property of water that prevents the lathering of soap.
Synthetic detergents do not form such scums. Hard water forms deposits that clog plumbing; these deposits, called "scale", are composed of calcium carbonate, magnesium hydroxide, calcium sulfate. Calcium and magnesium carbonates tend to be deposited as off-white solids on the inside surfaces of pipes and heat exchangers; this precipitation is principally caused by thermal decomposition of bicarbonate ions but happens in cases where the carbonate ion is at saturation concentration. The resulting build-up of scale restricts the flow of water in pipes. In boilers, the deposits impair the flow of heat into water, reducing the heating efficiency and allowing the metal boiler components to overheat. In a pressurized system, this overheating can lead to failure of the boiler; the damage caused by calcium carbonate deposits varies on the crystalline form, for example, calcite or aragonite. The presence of ions in an electrolyte, in this case, hard water, can lead to galvanic corrosion, in which one metal will preferentially corrode when in contact with another type of metal, when both are in contact with an electrolyte.
The softening of hard water by ion exchange does not increase its corrosivity per se. Where lead plumbing is in use, softened water does not increase plumbo-solvency. In swimming pools, hard water is manifested by a cloudy, appearance to the water. Calcium and magnesium hydroxides are both soluble in water; the solubility of the hydroxides of the alkaline-earth metals to which calcium and magnesium belong increases moving down the column. Aqueous solutions of these metal hydroxides absorb carbon dioxide from the air, forming the insoluble carbonates, giving rise to the turbidity; this results from the pH being excessively high. Hence, a common solution to the problem is, while maintaining the chlorine concentration at the proper level, to lower the pH by the addition of hydrochloric acid, the optimum value being in the range of 7.2 to 7.6. It is desirable to soften hard water. Most detergents contain ingredients. For this reason, water soften
Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air, its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium; the most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life. The name derives from Latin calx "lime", obtained from heating limestone; some calcium compounds were known to the ancients, though their chemistry was unknown until the seventeenth century. Pure calcium was isolated in 1808 via electrolysis of its oxide by Humphry Davy, who named the element. Calcium compounds are used in many industries: in foods and pharmaceuticals for calcium supplementation, in the paper industry as bleaches, as components in cement and electrical insulators, in the manufacture of soaps.
On the other hand, the metal in pure form has few applications due to its high reactivity. Calcium is the fifth-most abundant element in the human body; as electrolytes, calcium ions play a vital role in the physiological and biochemical processes of organisms and cells: in signal transduction pathways where they act as a second messenger. Calcium ions outside cells are important for maintaining the potential difference across excitable cell membranes as well as proper bone formation. Calcium is a ductile silvery metal whose properties are similar to the heavier elements in its group, strontium and radium. A calcium atom has twenty electrons, arranged in the electron configuration 4s2. Like the other elements placed in group 2 of the periodic table, calcium has two valence electrons in the outermost s-orbital, which are easily lost in chemical reactions to form a dipositive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is always divalent in its compounds, which are ionic.
Hypothetical univalent salts of calcium would be stable with respect to their elements, but not to disproportionation to the divalent salts and calcium metal, because the enthalpy of formation of MX2 is much higher than those of the hypothetical MX. This occurs because of the much greater lattice energy afforded by the more charged Ca2+ cation compared to the hypothetical Ca+ cation. Calcium, strontium and radium are always considered to be alkaline earth metals. Beryllium and magnesium are different from the other members of the group in their physical and chemical behaviour: they behave more like aluminium and zinc and have some of the weaker metallic character of the post-transition metals, why the traditional definition of the term "alkaline earth metal" excludes them; this classification is obsolete in English-language sources, but is still used in other countries such as Japan. As a result, comparisons with strontium and barium are more germane to calcium chemistry than comparisons with magnesium.
Calcium metal melts at 842 °C and boils at 1494 °C. It crystallises in the face-centered cubic arrangement like strontium, its density of 1.55 g/cm3 is the lowest in its group. Calcium can be cut with a knife with effort. While calcium is a poorer conductor of electricity than copper or aluminium by volume, it is a better conductor by mass than both due to its low density. While calcium is infeasible as a conductor for most terrestrial applications as it reacts with atmospheric oxygen, its use as such in space has been considered; the chemistry of calcium is that of a typical heavy alkaline earth metal. For example, calcium spontaneously reacts with water more than magnesium and less than strontium to produce calcium hydroxide and hydrogen gas, it reacts with the oxygen and nitrogen in the air to form a mixture of calcium oxide and calcium nitride. When finely divided, it spontaneously burns in air to produce the nitride. In bulk, calcium is less reactive: it forms a hydration coating in moist air, but below 30% relative humidity it may be stored indefinitely at room temperature.
Besides the simple oxide CaO, the peroxide CaO2 can be made by direct oxidation of calcium metal under a high pressure of oxygen, there is some evidence for a yellow superoxide Ca2. Calcium hydroxide, Ca2, is a strong base, though it is not as strong as the hydroxides of strontium, barium or the alkali metals. All four dihalides of calcium are known. Calcium carbonate and calcium sulfate are abundant minerals. Like strontium and barium, as well as the alkali metals and the divalent lanthanides europium and ytterbium, calcium metal dissolves directly in liquid ammonia to give a dark blue solution. Due to the large size of the Ca2+ ion, high coordination numbers are common, up to 24 in some intermetallic compounds such as CaZn13. Calcium is complexed by oxygen chelates such as EDTA and polyphosphates, which are useful in an
The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite and is the main component of pearls and the shells of marine organisms and eggs. Calcium carbonate is the active ingredient in agricultural lime and is created when calcium ions in hard water react with carbonate ions to create limescale, it is medicinally used as a calcium supplement or as an antacid, but excessive consumption can be hazardous. Calcium carbonate shares the typical properties of other carbonates. Notably it reacts with acids, releasing carbon dioxide:CaCO3 + 2 H+ → Ca2+ + CO2 + H2Oreleases carbon dioxide upon heating, called a thermal decomposition reaction, or calcination, to form calcium oxide called quicklime, with reaction enthalpy 178 kJ/mol:CaCO3 → CaO + CO2Calcium carbonate will react with water, saturated with carbon dioxide to form the soluble calcium bicarbonate. CaCO3 + CO2 + H2O → Ca2This reaction is important in the erosion of carbonate rock, forming caverns, leads to hard water in many regions.
An unusual form of calcium carbonate is the hexahydrate, ikaite, CaCO3·6H2O. Ikaite is stable only below 8 °C; the vast majority of calcium carbonate used in industry is extracted by quarrying. Pure calcium carbonate, can be produced from a pure quarried source. Alternatively, calcium carbonate is prepared from calcium oxide. Water is added to give calcium hydroxide carbon dioxide is passed through this solution to precipitate the desired calcium carbonate, referred to in the industry as precipitated calcium carbonate: CaO + H2O → Ca2 Ca2 + CO2 → CaCO3↓ + H2O The thermodynamically stable form of CaCO3 under normal conditions is hexagonal β-CaCO3. Other forms can be prepared, the denser orthorhombic λ-CaCO3 and μ-CaCO3, occurring as the mineral vaterite; the aragonite form can be prepared by precipitation at temperatures above 85 °C, the vaterite form can be prepared by precipitation at 60 °C. Calcite contains calcium atoms coordinated by six oxygen atoms, in aragonite they are coordinated by nine oxygen atoms.
The vaterite structure is not understood. Magnesium carbonate has the calcite structure, whereas strontium carbonate and barium carbonate adopt the aragonite structure, reflecting their larger ionic radii. Calcite and vaterite are pure calcium carbonate minerals. Industrially important source rocks which are predominantly calcium carbonate include limestone, chalk and travertine. Eggshells, snail shells and most seashells are predominantly calcium carbonate and can be used as industrial sources of that chemical. Oyster shells have enjoyed recent recognition as a source of dietary calcium, but are a practical industrial source. Dark green vegetables such as broccoli and kale contain dietarily significant amounts of calcium carbonate, they are not practical as an industrial source. Beyond Earth, strong evidence suggests the presence of calcium carbonate on Mars. Signs of calcium carbonate have been detected at more than one location; this provides some evidence for the past presence of liquid water.
Carbonate, is found in geologic settings and constitutes an enormous carbon reservoir. Calcium carbonate occurs as aragonite and dolomite as significant constituents of the calcium cycle; the carbonate minerals form the rock types: limestone, marble, travertine and others. In warm, clear tropical waters corals are more abundant than towards the poles where the waters are cold. Calcium carbonate contributors, including plankton, coralline algae, brachiopods, echinoderms and mollusks, are found in shallow water environments where sunlight and filterable food are more abundant. Cold-water carbonates do exist at higher latitudes but have a slow growth rate; the calcification processes are changed by ocean acidification. Where the oceanic crust is subducted under a continental plate sediments will be carried down to warmer zones in the asthenosphere and lithosphere. Under these conditions calcium carbonate decomposes to produce carbon dioxide which, along with other gases, give rise to explosive volcanic eruptions.
The carbonate compensation depth is the point in the ocean where the rate of precipitation of calcium carbonate is balanced by the rate of dissolution due to the conditions present. Deep in the ocean, the temperature pressure increases. Calcium carbonate is unusual in. Increasing pressure increases the solubility of calcium carbonate; the carbonate compensation depth can range from 4,000 to 6,000 meters below sea level. Calcium carbonate can preserve fossils through permineralization. Most of the vertebrate fossils of the Two Medicine Formation—a geologic formation known for its duck-billed dinosaur eggs—are preserved by CaCO3 permineralization; this type of preservation conserves high levels of detail down to the microscopic level. However, it leaves specimens vulnerable to weathering when exposed to the surface. Trilobite populations were once thought to have composed the majority of aquatic life during the Cambrian, due to the fact that their calcium carbonate-rich shells were more preserved than those of other species, which had purely chitinous shells.
The main use of calcium ca
Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid, it occurs as the mineral fluorite, deeply coloured owing to impurities. The compound crystallizes in a cubic motif called the fluorite structure. Ca2 + centres are eight-coordinate; each F− centre is coordinated to four Ca2+ centres. Although packed crystalline samples are colorless, the mineral is deeply colored due to the presence of F-centers; the same crystal structure is found in numerous ionic compounds with formula AB2, such as CeO2, cubic ZrO2, UO2, ThO2, PuO2. A related structure is the antifluorite structure, where the anions and cations are swapped, such as Be2C; the mineral fluorite is abundant, of interest as a precursor to HF. Thus, little motivation exists for the industrial production of CaF2. High purity CaF2 is produced by treating calcium carbonate with hydrofluoric acid: CaCO3 + 2 HF → CaF2 + CO2 + H2O Naturally occurring CaF2 is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials.
Calcium fluoride in the fluorite state is of significant commercial importance as a fluoride source. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid: CaF2 + H2SO4 → CaSO4 + 2 HF Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy and excimer lasers, it is transparent over a broad range from ultraviolet to infrared frequencies. Its low refractive index reduces the need for anti-reflection coatings, its insolubility in water is convenient as well. Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces toxic hydrofluoric acid. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air. List of laser types Photolithography Skeletal fluorosis NIST webbook thermochemistry data Charles Townes on the history of lasers National Pollutant Inventory - Fluoride and compounds fact sheet Crystran Material Data MSDS
Calcium carbide known as calcium acetylide, is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of calcium cyanamide; the pure material is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2. In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic. Applications of calcium carbide include manufacture of acetylene gas, for generation of acetylene in carbide lamps. Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at 2,200 °C; this method has not changed since its invention in 1892: CaO + 3 C → CaC2 + COThe high temperature required for this reaction is not achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The carbide product produced contains around 80% calcium carbide by weight; the carbide is crushed to produce small lumps.
The impurities are concentrated in the finer fractions. The CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis; as an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively. Impurities present in the carbide include phosphide; this reaction was an important part of the industrial revolution in chemistry, was made possible in the United States as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century. The method for the production in an electric arc furnace was discovered in 1892 by T. L Willson and independently by H. Moissan in the same year. In Bosnia and Herzegovina town of Jajce Austrian industrialist, Dr. Josef Kranz and his "Bosnische-Elektrizitäts AG" company, whose successor became "Elektro-Bosna", opened the largest chemical factory for production of calcium-carbide at the time in Europe in 1899. Hydroelectric power station on the Pliva river with installed capacity of 8 MW was constructed to supply electricity for the factory.
It was the first power station of its kind in Southeast Europe, which became operational on 24. March 1899. Pure calcium carbide is a colourless solid; the common crystalline form at room temperature is a distorted rock-salt structure with the C22− units lying parallel. The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862. CaC2 + 2H2O → C2H2 + Ca2This reaction was the basis of the industrial manufacture of acetylene, is the major industrial use of calcium carbide. Today acetylene is manufactured by the partial combustion of methane or appears as a side product in the ethylene stream from cracking of hydrocarbons. 400,000 tonnes are produced this way annually. In China, acetylene derived from calcium carbide remains a raw material for the chemical industry, in particular for the production of polyvinyl chloride. Locally produced acetylene is more economical than using imported oil. Production of calcium carbide in China has been increasing.
In 2005 output was 8.94 million tons, with the capacity to produce 17 million tons. In the United States and Japan, consumption of calcium carbide is declining. Production levels in the US during the 1990s were 236,000 tons per year. Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide: CaC2 + N2 → CaCN2 + CCommonly known as nitrolime, calcium cyanamide is used as fertilizer, it is hydrolysed to cyanamide, H2NCN. Calcium carbide is used: in the desulfurisation of iron as a fuel in steelmaking to extend the scrap ratio to liquid iron, depending on economics; as a powerful deoxidizer at ladle treatment facilities. Calcium carbide is used in carbide lamps. Water dripping on carbide produces acetylene gas, which produces light. While these lamps gave steadier and brighter light than candles, they were dangerous in coal mines, where flammable methane gas made them a serious hazard; the presence of flammable gases in coal mines led to miner safety lamps such as the Davy lamp, in which a wire gauze reduces the risk of methane ignition.
Carbide lamps were still used extensively in slate and tin mines where methane is not a serious hazard. Most miners' lamps have now been replaced by electric lamps. Carbide lamps are still used for mining in some less wealthy countries, for example in the silver mines near Potosí, Bolivia. Carbide lamps are still used by some cavers exploring caves and other underground areas, although they are being replaced in this use by LED lights. Carbide lamps were used extensively as headlights in early automobiles and bicycles, but have been replaced by electric lamps. Calcium carbide is sometimes used as source of acetylene gas, a ripening agent similar to ethylene. However, this is illegal in some countries as, in the production of acetylene from calcium carbide, contamination leads to trace production of phosphine and arsine; these impurities can be removed by passing the acetylene gas through acidified copper sulfate solution, but, in developing countries, this precaution is neglected. Calcium carbide is used in toy cannons such as the Big-Bang Cannon, as well as in bamboo cannons.
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