Bismuth is a chemical element with symbol Bi and atomic number 83. It is a pentavalent post-transition metal and one of the pnictogens with chemical properties resembling its lighter homologs arsenic and antimony. Elemental bismuth may occur although its sulfide and oxide form important commercial ores; the free element is 86% as dense as lead. It is a brittle metal with a silvery white color when freshly produced, but surface oxidation can give it a pink tinge. Bismuth is the most diamagnetic element, has one of the lowest values of thermal conductivity among metals. Bismuth was long considered the element with the highest atomic mass, stable, but in 2003 it was discovered to be weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe; because of its tremendously long half-life, bismuth may still be considered stable for all purposes. Bismuth metal has been known since ancient times, although it was confused with lead and tin, which share some physical properties.
The etymology is uncertain, but comes from Arabic bi ismid, meaning having the properties of antimony or the German words weiße Masse or Wismuth, translated in the mid-sixteenth century to New Latin bisemutum. Bismuth compounds account for about half the production of bismuth, they are used in cosmetics, a few pharmaceuticals, notably bismuth subsalicylate, used to treat diarrhea. Bismuth's unusual propensity to expand as it solidifies is responsible for some of its uses, such as in casting of printing type. Bismuth has unusually low toxicity for a heavy metal; as the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys as a replacement for lead. The name bismuth dates from around the 1660s, is of uncertain etymology, it is one of the first 10 metals to have been discovered. Bismuth appears in the 1660s, from obsolete German Bismuth, Wissmuth; the New Latin bisemutum is from the German Wismuth from weiße Masse, "white mass". The element was confused in early times with tin and lead because of its resemblance to those elements.
Bismuth has been known since ancient times, so no one person is credited with its discovery. Agricola, in De Natura Fossilium states that bismuth is a distinct metal in a family of metals including tin and lead; this was based on observation of their physical properties. Miners in the age of alchemy gave bismuth the name tectum argenti, or "silver being made," in the sense of silver still in the process of being formed within the Earth. Beginning with Johann Heinrich Pott in 1738, Carl Wilhelm Scheele and Torbern Olof Bergman, the distinctness of lead and bismuth became clear, Claude François Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin. Bismuth was known to the Incas and used in a special bronze alloy for knives. Bismuth is a brittle metal with a white, silver-pink hue with an iridescent oxide tarnish showing many colors from yellow to blue; the spiral, stair-stepped structure of bismuth crystals is the result of a higher growth rate around the outside edges than on the inside edges.
The variations in the thickness of the oxide layer that forms on the surface of the crystal cause different wavelengths of light to interfere upon reflection, thus displaying a rainbow of colors. When burned in oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes, its toxicity is much lower than that of its neighbors in the periodic table, such as lead and polonium. No other metal is verified to be more diamagnetic than bismuth. Of any metal, it has one of the lowest values of thermal conductivity and the highest Hall coefficient, it has a high electrical resistivity. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal. Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with germanium, silicon and water. Bismuth expands 3.32% on solidification. Though unseen in nature, high-purity bismuth can form distinctive, colorful hopper crystals, it is nontoxic and has a low melting point just above 271 °C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.
At ambient conditions bismuth shares the same layered structure as the metallic forms of arsenic and antimony, crystallizing in the rhombohedral lattice, classed into trigonal or hexagonal crystal systems. When compressed at room temperature, this Bi-I structure changes first to the monoclinic Bi-II at 2.55 GPa to the tetragonal Bi-III at 2.7 GPa, to the body-centered cubic Bi-IV at 7.7 GPa. The corresponding transitions can be monitored via changes in electrical conductivity. Bismuth is stable to both moist air at ordinary temperatures; when red-hot, it reacts with water to make bismuth oxide. 2 Bi + 3 H2O → Bi2O3 + 3 H2It reacts with fluorine to
Tellurium is a chemical element with symbol Te and atomic number 52. It is a brittle, mildly toxic, silver-white metalloid. Tellurium is chemically related to all three of which are chalcogens, it is found in native form as elemental crystals. Tellurium is far more common in the Universe as a whole than on Earth, its extreme rarity in the Earth's crust, comparable to that of platinum, is due its formation of a volatile hydride that caused tellurium to be lost to space as a gas during the hot nebular formation of Earth, to tellurium’s low affinity for oxygen that causes it to bind preferentially to other chalcophiles in dense minerals that sink into the core. Tellurium-bearing compounds were first discovered in 1782 in a gold mine in Kleinschlatten, Transylvania by Austrian mineralogist Franz-Joseph Müller von Reichenstein, although it was Martin Heinrich Klaproth who named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals are the most notable natural gold compounds.
However, they are not a commercially significant source of tellurium itself, extracted as a by-product of copper and lead production. Commercially, the primary use of tellurium is copper and steel alloys, where it improves machinability. Applications in CdTe solar panels and semiconductors consume a considerable portion of tellurium production. Tellurium is considered a technology-critical element. Tellurium has no biological function, although fungi can use it in place of sulfur and selenium in amino acids such as tellurocysteine and telluromethionine. In humans, tellurium is metabolized into dimethyl telluride, 2Te, a gas with a garlic-like odor exhaled in the breath of victims of tellurium exposure or poisoning. Tellurium has two allotropes and amorphous; when crystalline, tellurium is silvery-white with a metallic luster. It is a brittle and pulverized metalloid. Amorphous tellurium is a black-brown powder prepared by precipitating it from a solution of tellurous acid or telluric acid. Tellurium is a semiconductor that shows a greater electrical conductivity in certain directions depending on atomic alignment.
When molten, tellurium is corrosive to copper and stainless steel. Of the chalcogens, tellurium has the highest melting and boiling points, at 722.66 K and 1,261 K, respectively. Tellurium adopts a polymeric structure consisting of zig-zag chains of Te atoms; this gray material is not volatile. Occurring tellurium has eight isotopes. Six of those isotopes, 120Te, 122Te, 123Te, 124Te, 125Te, 126Te, are stable; the other two, 128Te and 130Te, have been found to be radioactive, with long half-lives, including 2.2 × 1024 years for 128Te. This is the longest known half-life among all radionuclides and is about 160 trillion times the age of the known universe. Stable isotopes comprise only 33.2% of occurring tellurium. A further 30 artificial radioisotopes of tellurium are known, with atomic masses ranging from 105 to 142 and with half-lives of 19 days or less. 17 nuclear isomers are known, with half-lives up to 154 days. Tellurium are among the lightest elements known to undergo alpha decay; the atomic mass of tellurium exceeds that of the next element in the periodic table.
With an abundance in the Earth's crust comparable to that of platinum, tellurium is one of the rarest stable solid elements. In comparison the rarest of the stable lanthanides have crustal abundances of 500 µg/kg; this rarity of tellurium in the Earth's crust is not a reflection of its cosmic abundance. Tellurium is more abundant than rubidium in the cosmos, though rubidium is 10,000 times more abundant in the Earth's crust; the rarity of tellurium on Earth is thought to be caused by conditions during preaccretional sorting in the solar nebula, when the stable form of certain elements, in the absence of oxygen and water, was controlled by the reductive power of free hydrogen. Under this scenario, certain elements that form volatile hydrides, such as tellurium, were depleted through evaporation of these hydrides. Tellurium and selenium are the heavy elements most depleted by this process. Tellurium is sometimes found in its native form, but is more found as the tellurides of gold such as calaverite and krennerite, petzite, Ag3AuTe2, sylvanite, AgAuTe4.
The city of Telluride, was named in hope of a strike of gold telluride. Gold itself is found uncombined, but when found as a chemical compound, it is most combined with tellurium. Although tellurium is found with gold more than in uncombined form, it is found more combined as tellurides of more common metals. Natural tellurite and tellurate minerals occur, formed by oxidation of tellurides near the Earth's surface. In contrast to selenium, tellurium does not replace sulfur in minerals because of the great difference in ion radii. Thus, many common sulfide minerals contain substantial quantities of selenium and only traces of tellurium. In the gold rush of 1893, miners in Kalgoorlie discarded a pyritic material as they searched for pure gold, it was used to fill in potholes and build sidewalks. In 1896, that tailing was discovered to be calaverite, a telluride of gold, it sparked a second gold rush that included mining the streets. Tellurium w
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
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
Halite known as rock salt, is a type of salt, the mineral form of sodium chloride. Halite forms isometric crystals; the mineral is colorless or white, but may be light blue, dark blue, pink, orange, yellow or gray depending on inclusion of other materials and structural or isotopic abnormalities in the crystals. It occurs with other evaporite deposit minerals such as several of the sulfates and borates; the name halite is derived from the Ancient Greek word for salt, ἅλς. Halite occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes and seas. Salt beds may underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan Basin. Other deposits are in Ohio, New Mexico, Nova Scotia and Saskatchewan; the Khewra salt mine is a massive deposit of halite near Pakistan. Salt domes are vertical diapirs or pipe-like masses of salt that have been "squeezed up" from underlying salt beds by mobilization due to the weight of overlying rock.
Salt domes contain anhydrite and native sulfur, in addition to halite and sylvite. They are common along the Gulf coasts of Texas and Louisiana and are associated with petroleum deposits. Germany, the Netherlands and Iran have salt domes. Salt glaciers exist in arid Iran where the salt has broken through the surface at high elevation and flows downhill. In all of these cases, halite is said to be behaving in the manner of a rheid. Unusual, fibrous vein filling halite is found in France and a few other localities. Halite crystals termed hopper crystals appear to be "skeletons" of the typical cubes, with the edges present and stairstep depressions on, or rather in, each crystal face. In a crystallizing environment, the edges of the cubes grow faster than the centers. Halite crystals form quickly in some evaporating lakes resulting in modern artifacts with a coating or encrustation of halite crystals. Halite flowers are rare stalactites of curling fibers of halite that are found in certain arid caves of Australia's Nullarbor Plain.
Halite stalactites and encrustations are reported in the Quincy native copper mine of Hancock, Michigan. The worlds largest underground salt mine is the Sifto Salt Mine, it uses the Room and Pillar Mining Method. It is located half a kilometre under Lake Huron in Canada. In the United Kingdom there are three mines. Salt is used extensively in cooking as a flavor enhancer, to cure a wide variety of foods such as bacon and fish, it is used in food preservation methods across various cultures. Larger pieces dusted over food from a shaker as finishing salt. Halite is often used both residentially and municipally for managing ice; because brine has a lower freezing point than pure water, putting salt or saltwater on ice, below 0 °C will cause it to melt. It is common for homeowners in cold climates to spread salt on their sidewalks and driveways after a snow storm to melt the ice, it is not necessary to use so much salt that the ice is melted. Many cities will spread a mixture of sand and salt on roads during and after a snowstorm to improve traction.
Using Salt Brine is more effective than spreading dry salt because moisture is necessary for the freezing-point depression to work and wet salt sticks to the roads better. Otherwise the salt can be wiped away by traffic. In addition to de-icing, rock salt is used in agriculture. An example of this would be inducing salt stress to suppress the growth of annual meadow grass in turf production. Other examples involve exposing weeds to salt water to dehydrate and kill them preventing them from affecting other plants. Salt is used as a household cleaning product, its coarse nature allows for its use in various cleaning scenarios including grease/oil removal, stain removal, dries out and hardens sticky spills for an easier clean. Some cultures in Africa and Brazil, prefer a wide variety of different rock salts for different dishes. Pure salt is avoided. Many recipes call for particular kinds of rock salt, imported pure salt has impurities added to adapt to local tastes. Salt was used as a form of currency in barter systems and was exlcusively controlled by authorities and their appointees.
In some ancient civilizations the practice of Salting The Earth was done to make conquered land of an enemy infertile and inhospitable as an act of domination. This act is known as Salting The Earth. We see biblical reference to this practice in Judges 9:45: “he killed the people in it, pulled the wall down and sowed the site with salt.”. Salt Coarse salt Salt tectonics
Rubidium is a chemical element with symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with a standard atomic weight of 85.4678. Elemental rubidium is reactive, with properties similar to those of other alkali metals, including rapid oxidation in air. On Earth, natural rubidium comprises two isotopes: 72% is the stable isotope, 85Rb. German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed technique, flame spectroscopy; the name comes from the Latin word rubidus, meaning the color of its emission spectrum. Rubidium's compounds have various chemical and electronic applications. Rubidium metal is vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms. Rubidium is not a known nutrient for any living organisms. However, rubidium ions have the same charge as potassium ions, are taken up and treated by animal cells in similar ways. Rubidium is a soft, silvery-white metal.
It is the second most electropositive of the stable alkali metals and melts at a temperature of 39.3 °C. Like other alkali metals, rubidium metal reacts violently with water; as with potassium and caesium, this reaction is vigorous enough to ignite the hydrogen gas it produces. Rubidium has been reported to ignite spontaneously in air, it forms amalgams with mercury and alloys with gold, caesium and potassium, but not lithium. Rubidium has a low ionization energy of only 406 kJ/mol. Rubidium and potassium show a similar purple color in the flame test, distinguishing the two elements requires more sophisticated analysis, such as spectroscopy. Rubidium chloride is the most used rubidium compound: among several other chlorides, it is used to induce living cells to take up DNA. Other common rubidium compounds are the corrosive rubidium hydroxide, the starting material for most rubidium-based chemical processes. Rubidium silver iodide has the highest room temperature conductivity of any known ionic crystal, a property exploited in thin film batteries and other applications.
Rubidium forms a number of oxides when exposed to air, including rubidium monoxide, Rb6O, Rb9O2. Rubidium forms salts with halides, producing rubidium fluoride, rubidium chloride, rubidium bromide, rubidium iodide. Although rubidium is monoisotopic, rubidium in the Earth's crust is composed of two isotopes: the stable 85Rb and the radioactive 87Rb. Natural rubidium is radioactive, with specific activity of about 670 Bq/g, enough to expose a photographic film in 110 days. Twenty four additional rubidium isotopes have been synthesized with half-lives of less than 3 months. Rubidium-87 has a half-life of 48.8×109 years, more than three times the age of the universe of ×109 years, making it a primordial nuclide. It substitutes for potassium in minerals, is therefore widespread. Rb has been used extensively in dating rocks. During fractional crystallization, Sr tends to concentrate in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, the progressing differentiation results in rocks with elevated Rb/Sr ratios.
The highest ratios occur in pegmatites. If the initial amount of Sr is known or can be extrapolated the age can be determined by measurement of the Rb and Sr concentrations and of the 87Sr/86Sr ratio; the dates indicate the true age of the minerals only if the rocks have not been subsequently altered. Rubidium-82, one of the element's non-natural isotopes, is produced by electron-capture decay of strontium-82 with a half-life of 25.36 days. With a half-life of 76 seconds, rubidium-82 decays by positron emission to stable krypton-82. Rubidium is the twenty-third most abundant element in the Earth's crust as abundant as zinc and rather more common than copper, it occurs in the minerals leucite, pollucite and zinnwaldite, which contain as much as 1% rubidium oxide. Lepidolite contains between 0.3% and 3.5% rubidium, is the commercial source of the element. Some potassium minerals and potassium chlorides contain the element in commercially significant quantities. Seawater contains an average of 125 µg/L of rubidium compared to the much higher value for potassium of 408 mg/L and the much lower value of 0.3 µg/L for caesium.
Because of its large ionic radius, rubidium is one of the "incompatible elements." During magma crystallization, rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last. Therefore, the largest deposits of rubidium and caesium are zone pegmatite ore bodies formed by this enrichment process; because rubidium substitutes for potassium in the crystallization of magma, the enrichment is far less effective than that of caesium. Zone pegmatite ore bodies containing mineable quantities of caesium as pollucite or the lithium minerals lepidolite are a source for rubidium as a by-product. Two notable sources of rubidium are th