Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more properly known as the plagioclase feldspar series; this was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826. The series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the mineral's crystal lattice structure. Plagioclase in hand samples is identified by its polysynthetic crystal twinning or'record-groove' effect. Plagioclase is a major constituent mineral in the Earth's crust, is an important diagnostic tool in petrology for identifying the composition and evolution of igneous rocks. Plagioclase is a major constituent of rock in the highlands of the Earth's moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars.
The composition of a plagioclase feldspar is denoted by its overall fraction of anorthite or albite, determined by measuring the plagioclase crystal's refractive index in crushed grain mounts, or its extinction angle in thin section under a polarizing microscope. The extinction angle varies with the albite fraction. There are several named plagioclase feldspars that fall between anorthite in the series; the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, referring to its triclinic crystallization. Anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its unusually pure white color, it is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes with rarer minerals like tourmaline and beryl. The intermediate members of the plagioclase group are similar to each other and cannot be distinguished except by their optical properties.
The specific gravity in each member increases 0.02 per 10% increase in anorthite. Bytownite, named after the former name for Ottawa, Canada, is a rare mineral found in more basic rocks. Labradorite is the characteristic feldspar of the more basic rock types such as diorite, andesite, or basalt and is associated with one of the pyroxenes or amphiboles. Labradorite shows an iridescent display of colors due to light refracting within the lamellae of the crystal, it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite, composed entirely of plagioclase. A variety of labradorite known as spectrolite is found in Finland. Andesine is a characteristic mineral of rocks such as diorite which contain a moderate amount of silica and related volcanics such as andesite. Oligoclase is common in granite, syenite and gneiss, it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, in reference to the fact that its cleavage angle differs from 90°.
Sunstone is oligoclase with flakes of hematite. Hypersolvus List of minerals Subsolvus
Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz, metal oxides and organic matter. Geologic clay deposits are composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, become hard and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red. Although many occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. There is, some overlap in particle size and other physical properties; the distinction between silt and clay varies by discipline. Geologists and soil scientists consider the separation to occur at a particle size of 2 µm, sedimentologists use 4–5 μm, colloid chemists use 1 μm.
Geotechnical engineers distinguish between silts and clays based on the plasticity properties of the soil, as measured by the soils' Atterberg limits. ISO 14688 grades clay particles as being smaller than 2 silt particles as being larger. Mixtures of sand and less than 40% clay are called loam. Loam is used as a building material. Clay minerals form over long periods of time as a result of the gradual chemical weathering of rocks silicate-bearing, by low concentrations of carbonic acid and other diluted solvents; these solvents acidic, migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed through hydrothermal activity. There are two types of clay deposits: secondary. Primary clays remain at the site of formation. Secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit. Clay deposits are associated with low energy depositional environments such as large lakes and marine basins.
Depending on the academic source, there are three or four main groups of clays: kaolinite, montmorillonite-smectite and chlorite. Chlorites are not always considered to be a clay, sometimes being classified as a separate group within the phyllosilicates. There are 30 different types of "pure" clays in these categories, but most "natural" clay deposits are mixtures of these different types, along with other weathered minerals. Varve is clay with visible annual layers, which are formed by seasonal deposition of those layers and are marked by differences in erosion and organic content; this type of deposit is common in former glacial lakes. When fine sediments are delivered into the calm waters of these glacial lake basins away from the shoreline, they settle to the lake bed; the resulting seasonal layering is preserved in an distribution of clay sediment banding. Quick clay is a unique type of marine clay indigenous to the glaciated terrains of Norway, Northern Ireland, Sweden, it is a sensitive clay, prone to liquefaction, involved in several deadly landslides.
Powder X-ray diffraction can be used to identify clays. The physical and reactive chemical properties can be used to help elucidate the composition of clays. Clays exhibit plasticity. However, when dry, clay becomes firm and when fired in a kiln, permanent physical and chemical changes occur; these changes convert the clay into a ceramic material. Because of these properties, clay is used for making pottery, both utilitarian and decorative, construction products, such as bricks and floor tiles. Different types of clay, when used with different minerals and firing conditions, are used to produce earthenware and porcelain. Prehistoric humans discovered the useful properties of clay; some of the earliest pottery shards recovered are from Japan. They are associated with the Jōmon culture and deposits they were recovered from have been dated to around 14,000 BC. Clay tablets were the first known writing medium. Scribes wrote by inscribing them with cuneiform script using a blunt reed called a stylus. Purpose-made clay balls were used as sling ammunition.
Clays sintered in fire were the first form of ceramic. Bricks, cooking pots, art objects, smoking pipes, musical instruments such as the ocarina can all be shaped from clay before being fired. Clay is used in many industrial processes, such as paper making, cement production, chemical filtering; until the late 20th century, bentonite clay was used as a mold binder in the manufacture of sand castings. Clay, being impermeable to water, is used where natural seals are needed, such as in the cores of dams, or as a barrier in landfills against toxic seepage. Studies in the early 21st century have investigated clay's absorption capacities in various applications, such as the removal of heavy metals from waste water and air purification. Traditional uses of clay as medicine goes back to prehistoric times. An example is Armenian bole, used to soothe an upset stomach; some animals such as parrots and pigs ingest clay for similar reasons. Kaolin clay and attapulgite have been used as anti-diarrheal medicines.
Clay as the defining ingredient of loam is one of the oldest building materials on Earth, among other
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light propagates through the material. It is defined as n = c v, where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times as fast in vacuum as in water. The refractive index determines how much the path of light is bent, or refracted, when entering a material; this is described by Snell's law of refraction, n1 sinθ1 = n2 sinθ2, where θ1 and θ2 are the angles of incidence and refraction of a ray crossing the interface between two media with refractive indices n1 and n2. The refractive indices determine the amount of light, reflected when reaching the interface, as well as the critical angle for total internal reflection and Brewster's angle; the refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, the wavelength in that medium is λ = λ0/n, where λ0 is the wavelength of that light in vacuum.
This implies that vacuum has a refractive index of 1, that the frequency of the wave is not affected by the refractive index. As a result, the energy of the photon, therefore the perceived color of the refracted light to a human eye which depends on photon energy, is not affected by the refraction or the refractive index of the medium. While the refractive index affects wavelength, it depends on photon frequency and energy so the resulting difference in the bending angle causes white light to split into its constituent colors; this is called dispersion. It can be observed in prisms and rainbows, chromatic aberration in lenses. Light propagation in absorbing materials can be described using a complex-valued refractive index; the imaginary part handles the attenuation, while the real part accounts for refraction. The concept of refractive index applies within the full electromagnetic spectrum, from X-rays to radio waves, it can be applied to wave phenomena such as sound. In this case the speed of sound is used instead of that of light, a reference medium other than vacuum must be chosen.
The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, the phase velocity v of light in the medium, n = c v. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves; the definition above is sometimes referred to as the absolute refractive index or the absolute index of refraction to distinguish it from definitions where the speed of light in other reference media than vacuum is used. Air at a standardized pressure and temperature has been common as a reference medium. Thomas Young was the person who first used, invented, the name "index of refraction", in 1807. At the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers; the ratio had the disadvantage of different appearances. Newton, who called it the "proportion of the sines of incidence and refraction", wrote it as a ratio of two numbers, like "529 to 396".
Hauksbee, who called it the "ratio of refraction", wrote it as a ratio with a fixed numerator, like "10000 to 7451.9". Hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in 1807. In the next years, others started using different symbols: n, m, µ; the symbol n prevailed. For visible light most transparent media have refractive indices between 1 and 2. A few examples are given in the adjacent table; these values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, as is conventionally done. Gases at atmospheric pressure have refractive indices close to 1 because of their low density. All solids and liquids have refractive indices above 1.3, with aerogel as the clear exception. Aerogel is a low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the other end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, but some high-refractive-index polymers can have values as high as 1.76.
For infrared light refractive indices can be higher. Germanium is transparent in the wavelength region from 2 to 14 µm and has a refractive index of about 4. A type of new materials, called topological insulator, was found holding higher refractive index of up to 6 in near to mid infrared frequency range. Moreover, topological insulator material are transparent; these excellent properties make them a type of significant materials for infrared optics. According to the theory of relativity, no information can travel faster than the speed of light in vacuum, but this does not mean that the refractive index cannot be lower than 1; the refractive index measures the phase velocity of light. The phase velocity is the speed at which the crests of the wave move and can be faster than the speed of light in vacuum, thereby give a refractive index below 1; this can occur close to resonance frequencies, for absorbing media, in plasmas, for X-rays. In the X-ray regime the refractive indices are
Perthite is used to describe an intergrowth of two feldspars: a host grain of potassium-rich alkali feldspar includes exsolved lamellae or irregular intergrowths of sodic alkali feldspar. The host grain is orthoclase or microcline, the lamellae are albite. If sodic feldspar is the dominant phase, the result is an antiperthite and where the feldspars are in equal proportions the result is a mesoperthite; the intergrowth forms by exsolution due to cooling of a grain of alkali feldspar with a composition intermediate between K-feldspar and albite. There is complete solid solution between albite and K-feldspar at temperatures near 700 °C and pressures like those within the crust of the Earth, but a miscibility gap is present at lower temperatures. If an alkali feldspar grain with an intermediate composition cools enough, K-rich and more Na-rich feldspar domains separate from one another. In the presence of water, the process occurs quickly; when megascopically developed, the texture may consist of distinct pink and white lamellae representing exsolved white albite in pink microcline.
The intergrowths in perthite have a great variety of shapes. If cooling is sufficiently slow, the alkali feldspar may exsolve to form separate grains with near-endmember albite and K-feldspar compositions; the largest documented single crystal of perthite was found in Hugo Mine in South Dakota and measured about 10.7 m x 4.6 m x 1.8 m. The gem varieties of potassium feldspar and moonstone are variant colored perthites. R. V. Dietrich - Perthite
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. It is the volcanic equivalent of syenite; the mineral assemblage consists of essential alkali feldspar. Biotite and olivine are common accessory minerals. Chemically, trachyte contains 60 to 65% silica content; these chemical differences are consistent with the position of trachyte in the TAS classification, they account for the feldspar-rich mineralogy of the rock type. Trachytes consist of sanidine feldspar, they have minute irregular steam cavities which make the broken surfaces of specimens of these rocks rough and irregular, from this character they have derived their name. It was first given to certain rocks of this class from Auvergne, was long used in a much wider sense than that defined above; the trachytes are described as being the volcanic equivalents of the plutonic syenites. Their dominant mineral, sanidine feldspar commonly occurs in two generations, i.e. both as large well-shaped porphyritic crystals and in smaller imperfect rods or laths forming a finely crystalline groundmass.
With this there is always a smaller amount of plagioclase oligoclase. Rhomb porphyry is an example with large porphyritic rhomb shaped phenocrysts embedded in a fine-grained matrix. Quartz is rare in trachyte, but tridymite is by no means uncommon, it is in crystals large enough to be visible without the aid of the microscope, but in thin sections it may appear as small hexagonal plates, which overlap and form dense aggregates, like a mosaic or like the tiles on a roof. They cover the surfaces of the larger feldspars or line the steam cavities of the rock, where they may be mingled with amorphous opal or fibrous chalcedony. In the older trachytes, secondary quartz is not rare, sometimes results from the recrystallization of tridymite. Of the mafic minerals present, augite is the most common, it is of pale green color, its small crystals are very perfect in form. Brown hornblende and biotite occur and are surrounded by black corrosion borders composed of magnetite and pyroxene. Olivine is unusual, though found like those of the Arso in Ischia.
Basic varieties of plagioclase, such as labradorite, are known as phenocrysts in some Italian trachytes. Dark brown varieties of augite and rhombic pyroxene are not common. Apatite and magnetite are always present as accessory minerals. Trachytes, being rich in potassium feldspar contain considerable amounts of alkali. Minerals of the feldspathoid group, such as nepheline and leucite, rocks of this kind are known as phonolitic trachytes; the sodium-bearing amphiboles and pyroxenes so characteristic of the phonolites may be found in some trachytes. Trachytic rocks are porphyritic, some of the best known examples, such as the trachyte of Drachenfels on the Rhine, show this character excellently, having large sanidine crystals of tabular form an inch or two in length scattered through their fine-grained groundmass. In many trachytes, the phenocrysts are few and small, the groundmass comparatively coarse; the ferromagnesian minerals occur in large crystals, are not conspicuous in hand specimens of these rocks.
Two types of groundmass are recognized: the trachytic, composed of long, subparallel rods of sanidine, the orthophyric, consisting of small squarish or rectangular prisms of the same mineral. Sometimes granular augite or spongy riebeckite occurs in the groundmass, but as a rule this part of the rock is feldspathic. Glassy forms of trachyte occur, as in Iceland, pumiceous varieties are known, but these rocks as contrasted with the rhyolites have a remarkably strong tendency to crystallize, are to any considerable extent vitreous. Trachytes are well represented among the Cenozoic volcanic rocks of Europe. In Britain they occur in Skye as lava flows and as dikes or intrusions, but they are much more common on the continent of Europe, as in the Rhine district and the Eifel in Auvergne and the Euganean Hills. In the neighborhood of Rome and the island of Ischia trachytic lavas and tuffs are of common occurrence. Trachytes are found on the island of Pantelleria. In the United States, trachytes crop out extensively in the Davis Mountains, Chisos Mountains, Big Bend Ranch State Park in the Big Bend region, as well as southern Nevada and South Dakota.
There is one known voluminous flow from Pu'u Wa'awa'a on the north flank of Hualalai in Hawaii. In Iceland, the Azores, Tenerife an
The mineral pyrite, or iron pyrite known as fool's gold, is an iron sulfide with the chemical formula FeS2. Pyrite is considered the most common of the sulfide minerals. Pyrite's metallic luster and pale brass-yellow hue give it a superficial resemblance to gold, hence the well-known nickname of fool's gold; the color has led to the nicknames brass and Brazil used to refer to pyrite found in coal. The name pyrite is derived from the Greek πυρίτης, "of fire" or "in fire", in turn from πύρ, "fire". In ancient Roman times, this name was applied to several types of stone that would create sparks when struck against steel. By Georgius Agricola's time, c. 1550, the term had become a generic term for all of the sulfide minerals. Pyrite is found associated with other sulfides or oxides in quartz veins, sedimentary rock, metamorphic rock, as well as in coal beds and as a replacement mineral in fossils, but has been identified in the sclerites of scaly-foot gastropods. Despite being nicknamed fool's gold, pyrite is sometimes found in association with small quantities of gold.
Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37% gold by weight. Pyrite enjoyed brief popularity in the 16th and 17th centuries as a source of ignition in early firearms, most notably the wheellock, where a sample of pyrite was placed against a circular file to strike the sparks needed to fire the gun. Pyrite has been used since classical times to manufacture copperas. Iron pyrite was allowed to weather; the acidic runoff from the heap was boiled with iron to produce iron sulfate. In the 15th century, new methods of such leaching began to replace the burning of sulfur as a source of sulfuric acid. By the 19th century, it had become the dominant method. Pyrite remains in commercial use for the production of sulfur dioxide, for use in such applications as the paper industry, in the manufacture of sulfuric acid. Thermal decomposition of pyrite into FeS and elemental sulfur starts at 540 °C. A newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium batteries.
Pyrite is a semiconductor material with a band gap of 0.95 eV. Pure pyrite is n-type, in both crystal and thin-film forms due to sulfur vacancies in the pyrite crystal structure acting as n-dopants. During the early years of the 20th century, pyrite was used as a mineral detector in radio receivers, is still used by crystal radio hobbyists; until the vacuum tube matured, the crystal detector was the most sensitive and dependable detector available – with considerable variation between mineral types and individual samples within a particular type of mineral. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs. Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector. Pyrite has been proposed as an abundant, non-toxic, inexpensive material in low-cost photovoltaic solar panels. Synthetic iron sulfide was used with copper sulfide to create the photovoltaic material.. More recent efforts are working toward thin-film solar cells made of pyrite.
Pyrite is used to make marcasite jewelry. Marcasite jewelry, made from small faceted pieces of pyrite set in silver, was known since ancient times and was popular in the Victorian era. At the time when the term became common in jewelry making, "marcasite" referred to all iron sulfides including pyrite, not to the orthorhombic FeS2 mineral marcasite, lighter in color and chemically unstable, thus not suitable for jewelry making. Marcasite jewelry does not contain the mineral marcasite. China represents the main importing country with an import of around 376,000 tonnes, which resulted at 45% of total global imports. China is the fastest growing in terms of the unroasted iron pyrites imports, with a CAGR of +27.8% from 2007 to 2016. In value terms, China constitutes the largest market for imported unroasted iron pyrites worldwide, making up 65% of global imports. From the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is best described as Fe2+S22−.
This formalism recognizes. These persulfide units can be viewed as derived from hydrogen disulfide, H2S2, thus pyrite would be more descriptively, not iron disulfide. In contrast, molybdenite, MoS2, features isolated sulfide centers and the oxidation state of molybdenum is Mo4+; the mineral arsenopyrite has the formula FeAsS. Whereas pyrite has S2 subunits, arsenopyrite has units, formally derived from deprotonation of H2AsSH. Analysis of classical oxidation states would recommend the description of arsenopyrite as Fe3+3−. Iron-pyrite FeS2 represents the prototype compound of the crystallographic pyrite structure; the structure is simple cubic and was among the first crystal structures solved by X-ray diffraction. It belongs to the crystallographic space group Pa3 and is denoted by the Strukturbericht notation C2. Under thermodynamic standard conditions the lattice constant a of stoichiometric iron pyrite FeS2 amounts to 541.87 pm. The unit cell is composed of a Fe face-centered cubic sublattice into.
The pyrite structure is used by other compounds MX2 of trans
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically similar to sodium, the previous element in group 1 of the periodic table, they have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, it is the most common radioisotope in the human body. Potassium ions are vital for the functioning of all living cells; the transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission. Fresh fruits and vegetables are good dietary sources of potassium; the body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s