In chemistry, an organic compound is any chemical compound that contains carbon. Due to carbon's ability to catenate, millions of organic compounds are known. Study of the properties and synthesis of organic compounds is the discipline known as organic chemistry. For historical reasons, a few classes of carbon-containing compounds, along with a handful of other exceptions, are not classified as organic compounds and are considered inorganic. No consensus exists among chemists on which carbon-containing compounds are excluded, making the definition of an organic compound elusive. Although organic compounds make up only a small percentage of the Earth's crust, they are of central importance because all known life is based on organic compounds. Living things incorporate inorganic carbon into organic compounds through a network of processes that begins with the conversion of carbon dioxide and a hydrogen source like water into simple sugars and other organic molecules by autotrophic organisms using light or other sources of energy.
Most synthetically produced organic compounds are derived from petrochemicals consisting of hydrocarbons, which are themselves formed from the high pressure and temperature degradation of organic matter underground over geological timescales. This ultimate derivation notwithstanding, organic compounds are no longer defined as compounds originating in living things, as they were historically. In chemical nomenclature, an organyl group represented by the letter R, refers to any monovalent substituent whose open valence is on a carbon atom. For historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, simple oxides of carbon, cyanides are considered inorganic. Allotropes of carbon, such as diamond, graphite and carbon nanotubes are excluded because they are simple substances composed of only a single element and therefore allotropes are not considered to be chemical compounds. For many centuries, Western physicians and chemists believed in vitalism; this was the widespread conception that substances found in organic nature are created from the chemical elements by the action of a "vital force" or "life-force" that only living organisms possess.
Vitalism taught that these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulations. Vitalism survived for a while after the rise of modern ideas about the atomic theory and chemical elements, it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhler's 1828 synthesis of urea from the inorganic salts potassium cyanate and ammonium sulfate. Urea had long been considered an "organic" compound, as it was known to occur only in the urine of living organisms. Wöhler's experiments were followed by many others, in which complex "organic" substances were produced from "inorganic" ones without the involvement of any living organism. Though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds; the modern meaning of organic compound is any compound that contains a significant amount of carbon—even though many of the organic compounds known today have no connection to any substance found in living organisms.
The term carbogenic has been proposed by E. J. Corey as a modern alternative to organic, but this neologism remains obscure; the organic compound L-isoleucine molecule presents some features typical of organic compounds: carbon–carbon bonds, carbon–hydrogen bonds, as well as covalent bonds from carbon to oxygen and to nitrogen. As described in detail below, any definition of organic compound that uses simple, broadly applicable criteria turns out to be unsatisfactory, to varying degrees; the modern accepted definition of organic compound amounts to any carbon containing compound, excluding several classes of substances traditionally considered as'inorganic'. However, the list of substances so excluded varies from author to author. Still, it is agreed upon that there are a few carbon containing compounds that should not be considered organic. For instance all authorities would require the exclusion of alloys that contain carbon, including steel, as well as other metal and semimetal carbides. Other compounds and materials that are considered'inorganic' by most authorities include: metal carbonates, simple oxides, the allotropes of carbon, cyanide derivatives not containing an organic residue, heavier analogs thereof.
Halides of carbon without hydrogen, carboranes, metal carbonyls, mellitic anhydride, other exotic oxocarbons are considered inorganic by some authorities. Nickel carbonyl and other metal carbonyls present an interesting case, they are volatile liquids, like many organic compounds, yet they contain only carbon bonded to a transition metal and to oxygen and are prepared directly from metal and carbon monoxide. Nickel carbonyl is considered to be organometallic. Although many organometalli
Quartz is a mineral composed of silicon and oxygen atoms in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral behind feldspar. Quartz exists in two forms, the normal α-quartz and the high-temperature β-quartz, both of which are chiral; the transformation from α-quartz to β-quartz takes place abruptly at 573 °C. Since the transformation is accompanied by a significant change in volume, it can induce fracturing of ceramics or rocks passing through this temperature threshold. There are many different varieties of quartz. Since antiquity, varieties of quartz have been the most used minerals in the making of jewelry and hardstone carvings in Eurasia; the word "quartz" is derived from the German word "Quarz", which had the same form in the first half of the 14th century in Middle High German in East Central German and which came from the Polish dialect term kwardy, which corresponds to the Czech term tvrdý.
The Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning "icy cold", because some philosophers believed the mineral to be a form of supercooled ice. Today, the term rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the trigonal crystal system; the ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end. In nature quartz crystals are twinned, distorted, or so intergrown with adjacent crystals of quartz or other minerals as to only show part of this shape, or to lack obvious crystal faces altogether and appear massive. Well-formed crystals form in a'bed' that has unconstrained growth into a void. However, doubly terminated crystals do occur where they develop without attachment, for instance within gypsum. A quartz geode is such a situation where the void is spherical in shape, lined with a bed of crystals pointing inward. Α-quartz crystallizes in the trigonal crystal system, space group P3121 or P3221 depending on the chirality.
Β-quartz belongs to space group P6222 and P6422, respectively. These space groups are chiral. Both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks; the transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, without change in the way they are linked. Although many of the varietal names arose from the color of the mineral, current scientific naming schemes refer to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, has been used for hardstone carvings, such as the Lothair Crystal. Common colored varieties include citrine, rose quartz, smoky quartz, milky quartz, others; these color differentiation's arise from chromophores which have been incorporated into the crystal structure of the mineral.
Polymorphs of quartz include: α-quartz, β-quartz, moganite, cristobalite and stishovite. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties; the cryptocrystalline varieties are either translucent or opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a cryptocrystalline form of silica consisting of fine intergrowths of both quartz, its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz including contrasting bands or patterns of color, are agate, carnelian or sard, onyx and jasper. Amethyst is a form of quartz that ranges from a dull purple color; the world's largest deposits of amethysts can be found in Brazil, Uruguay, France and Morocco. Sometimes amethyst and citrine are found growing in the same crystal, it is referred to as ametrine. An amethyst is formed. Blue quartz contains inclusions of fibrous crocidolite. Inclusions of the mineral dumortierite within quartz pieces result in silky-appearing splotches with a blue hue, shades giving off purple and/or grey colors additionally being found.
"Dumortierite quartz" will sometimes feature contrasting light and dark color zones across the material. Interest in the certain quality forms of blue quartz as a collectible gemstone arises in India and in the United States. Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare. However, a heat-treated amethyst will have small lines in the crystal, as opposed to a natural citrine's cloudy or smokey appearance, it is nearly impossible to differentiate between cut citrine and yellow topaz visually, but they differ in hardness. Brazil is the leading producer of citrine, with much
International Standard Book Number
The International Standard Book Number is a numeric commercial book identifier, intended to be unique. Publishers purchase ISBNs from an affiliate of the International ISBN Agency. An ISBN is assigned to each variation of a book. For example, an e-book, a paperback and a hardcover edition of the same book would each have a different ISBN; the ISBN is 13 digits long if assigned on or after 1 January 2007, 10 digits long if assigned before 2007. The method of assigning an ISBN is nation-based and varies from country to country depending on how large the publishing industry is within a country; the initial ISBN identification format was devised in 1967, based upon the 9-digit Standard Book Numbering created in 1966. The 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO 2108. Published books sometimes appear without an ISBN; the International ISBN agency sometimes assigns such books ISBNs on its own initiative.
Another identifier, the International Standard Serial Number, identifies periodical publications such as magazines and newspapers. The International Standard Music Number covers musical scores; the Standard Book Numbering code is a 9-digit commercial book identifier system created by Gordon Foster, Emeritus Professor of Statistics at Trinity College, for the booksellers and stationers WHSmith and others in 1965. The ISBN identification format was conceived in 1967 in the United Kingdom by David Whitaker and in 1968 in the United States by Emery Koltay; the 10-digit ISBN format was developed by the International Organization for Standardization and was published in 1970 as international standard ISO 2108. The United Kingdom continued to use the 9-digit SBN code until 1974. ISO has appointed the International ISBN Agency as the registration authority for ISBN worldwide and the ISBN Standard is developed under the control of ISO Technical Committee 46/Subcommittee 9 TC 46/SC 9; the ISO on-line facility only refers back to 1978.
An SBN may be converted to an ISBN by prefixing the digit "0". For example, the second edition of Mr. J. G. Reeder Returns, published by Hodder in 1965, has "SBN 340 01381 8" – 340 indicating the publisher, 01381 their serial number, 8 being the check digit; this can be converted to ISBN 0-340-01381-8. Since 1 January 2007, ISBNs have contained 13 digits, a format, compatible with "Bookland" European Article Number EAN-13s. An ISBN is assigned to each variation of a book. For example, an ebook, a paperback, a hardcover edition of the same book would each have a different ISBN; the ISBN is 13 digits long if assigned on or after 1 January 2007, 10 digits long if assigned before 2007. An International Standard Book Number consists of 4 parts or 5 parts: for a 13-digit ISBN, a prefix element – a GS1 prefix: so far 978 or 979 have been made available by GS1, the registration group element, the registrant element, the publication element, a checksum character or check digit. A 13-digit ISBN can be separated into its parts, when this is done it is customary to separate the parts with hyphens or spaces.
Separating the parts of a 10-digit ISBN is done with either hyphens or spaces. Figuring out how to separate a given ISBN is complicated, because most of the parts do not use a fixed number of digits. ISBN is most used among others special identifiers to describe references in Wikipedia and can help to find the same sources with different description in various language versions. ISBN issuance is country-specific, in that ISBNs are issued by the ISBN registration agency, responsible for that country or territory regardless of the publication language; the ranges of ISBNs assigned to any particular country are based on the publishing profile of the country concerned, so the ranges will vary depending on the number of books and the number and size of publishers that are active. Some ISBN registration agencies are based in national libraries or within ministries of culture and thus may receive direct funding from government to support their services. In other cases, the ISBN registration service is provided by organisations such as bibliographic data providers that are not government funded.
A full directory of ISBN agencies is available on the International ISBN Agency website. Partial listing: Australia: the commercial library services agency Thorpe-Bowker.
In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure in a rock formation or a vein of ore, deposited or embedded between layers of rock. The current meaning dates from the 17th century, being an expansion of an earlier sense of a "channel, watercourse" in late Middle English, which in turn is from the 11th-century meaning of lode as a ‘course, way’; the accepted hydrothermal model of lode deposition posits that metals dissolved in hydrothermal solutions deposit the gold or other metallic minerals inside the fissures in the pre-existing rocks. Lode deposits are distinguished from placer deposits, where the ore has been eroded out from its original depositional environment and redeposited by sedimentation. A third process for ore deposition is as an evaporite. A stringer lode is one in which the rock is so permeated by small veinlets that rather than mining the veins, the entire mass of ore and the enveined country rock is mined, it is so named because of the irregular branching of the veins into many anastomosing stringers, so that the ore is not separable from the country rock.
One of largest silver lodes was the Comstock Lode in Nevada, although it is overshadowed by the more discovered Cannington Lode in Queensland, Australia. The largest gold lode in the United States was the Homestake Lode; the Broken Hill Lode in South Australia is the largest lead-zinc lode discovered. Lodestone, known just as lode in the 16th and 17th centuries. Mother lode, the principal vein Ore genesis Thickness
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, vaterite is less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime, calx with the suffix -ite used to name minerals, it is thus etymologically related to chalk. When applied by archaeologists and stone trade professionals, the term alabaster is used not just as in geology and mineralogy, where it is reserved for a variety of gypsum. In publications, two different sets of Miller indices are used to describe directions in calcite crystals - the hexagonal system with three indices h, k, l and the rhombohedral system with four indices h, k, l, i. To add to the complications, there are two definitions of unit cell for calcite.
One, an older "morphological" unit cell, was inferred by measuring angles between faces of crystals and looking for the smallest numbers that fit. A "structural" unit cell was determined using X-ray crystallography; the morphological unit cell has approximate dimensions a = 10 Å and c = 8.5 Å, while for the structural unit cell they are a = 5 Å and c = 17 Å. For the same orientation, c must be multiplied by 4 to convert from morphological to structural units; as an example, the cleavage is given as "perfect on " in morphological coordinates and "perfect on " in structural units. Twinning and crystal forms are always given in morphological units. Over 800 forms of calcite crystals have been identified. Most common are scalenohedra, with faces in the hexagonal directions or directions. Habits include acute to tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms, it may occur as fibrous, lamellar, or compact. A fibrous, efflorescent form is known as lublinite.
Cleavage is in three directions parallel to the rhombohedron form. Its fracture is difficult to obtain. Scalenohedral faces are chiral and come in pairs with mirror-image symmetry. Rhombohedral faces are achiral, it has a defining Mohs hardness of 3, a specific gravity of 2.71, its luster is vitreous in crystallized varieties. Color is white or none, though shades of gray, orange, green, violet, brown, or black can occur when the mineral is charged with impurities. Calcite is transparent to opaque and may show phosphorescence or fluorescence. A transparent variety called. Acute scalenohedral crystals are sometimes referred to as "dogtooth spar" while the rhombohedral form is sometimes referred to as "nailhead spar". Single calcite crystals display; this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669. At a wavelength of ≈590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively.
Between 190 and 1700 nm, the ordinary refractive index varies between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, dissolved ion concentrations. Although calcite is insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite. Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. When conditions are right for dissolution, the removal of calcite can increase the porosity and permeability of the rock, if it continues for a long period of time may result in the formation of caves.
On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, resulting in various forms of karst topography. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. Many other cultures have used the material for similar carved applications. High-grade optical calcite was used in World War II for gun sights in bomb sights and anti-aircraft weaponry. Experiments have been conducted to use calcite for a cloak of invisibility. Microbiologically precipitated calcite has a wide range of applications, such as soil remediation, soil stabilization and concrete repair. Calcite, obtained from an 80 kg sample of Carrara marble, is used as the IAEA-603 isotopic standard in mass spectrometry for the calibration of δ18O and δ13C. Calcite is a common constituent