Abraham Gottlob Werner
Abraham Gottlob Werner was a German geologist who set out an early theory about the stratification of the Earth's crust and propounded a history of the Earth that came to be known as Neptunism. While most tenets of Neptunism were set aside, Werner is remembered for his demonstration of chronological succession in rocks, he has been called the "father of German geology". Werner was born in a village in Prussian Silesia, his family had been involved in the mining industry for many years. His father, Abraham David Werner, was a foreman at a foundry in Wehrau. Werner was educated at Freiberg and Leipzig, where he studied law and mining, was appointed as Inspector and Teacher of Mining and Mineralogy at the small, but influential, Freiberg Mining Academy in 1775. While in Leipzig, Werner became interested in the systematic identification and classification of minerals. Within a year he published the first modern textbook on descriptive mineralogy, Von den äusserlichen Kennzeichen der Fossilien. During his career, Werner published little, but his fame as a teacher spread throughout Europe, attracting students, who became virtual disciples, spread his interpretations throughout their homelands, e.g. Robert Jameson who became professor at Edinburgh and Andrés Manuel del Río who discovered vanadium.
Socratic in his lecturing style, Werner developed an appreciation for the broader implications and interrelations of geology within his students, who provided an enthusiastic and attentive audience. Werner's students Friedrich Mohs, Robert Jameson and G. Mitchell had plans to establish an institute analogous to Freiberg Mining Academy in Dublin, which were due to the death of some people involved never carried out. Werner was plagued by frail health his entire life, passed a quiet existence in the immediate environs of Freiberg. An avid mineral collector in his youth, he abandoned field work altogether in his life. There is no evidence that he had traveled beyond Saxony in his entire adult life, he died at Dresden from internal complications said to have been caused by his consternation over the misfortunes that had befallen Saxony during the Napoleonic Wars. He is buried in the Neuen Annenfriedhof in south-west Dresden; the grave is marked by a simple boulder inscribed with his name. He was elected a foreign member of the Royal Swedish Academy of Sciences in 1810.
Starting from the pre-existing traditions of stratigraphy and cosmogony in Europe, Werner applied superposition in a classification similar to that of Johann Gottlob Lehmann. He believed that the Earth could be divided into five formations: Primitive Series: intrusive igneous rocks and high rank metasediments considered to be the first precipitates from the ocean before the emergence of land. Transition Series: more indurated limestones, dikes and thick sequences of greywackes that were the first orderly deposits from the ocean; these were "universal" formations extending without interruption around the world. Secondary or Stratified Series: the remaining stratified fossiliferous rocks and certain associated "trap" rocks; these were thought to represent the emergence of mountains from beneath the ocean and were formed from the resulting products of erosion deposited on their flanks. Alluvial or Tertiary Series: poorly consolidated sands and clays formed by the withdrawal of the oceans from the continents.
Volcanic Series: younger lava flows demonstrably associated with volcanic vents. Werner believed; the basic concept of Wernerian geology was the belief in an all encompassing ocean that receded to its present location while precipitating or depositing all the rocks and minerals in the Earth's crust. The emphasis on this universal ocean spawned the term "Neptunism" that became applied to the concept and it became synonymous with Wernerian teaching, although Jean-Étienne Guettard in France originated the view. A universal ocean led directly to the idea of universal formations, which Werner believed could be recognized on the basis of lithology and superposition, he coined the term "geognosy" to define a science based on the recognition of the order and relation of the layers forming the Earth. Werner believed not theory, his followers resisted speculation, as a result Wernerian geognosy and Neptunism became dogma and ceased to contribute to further understanding of the history of the Earth. His former student Robert Jameson, who became Regius Professor at the University of Edinburgh, founded the Wernerian Natural History Society in 1808 honour of Werner, while debating many aspects of natural history, was a bastion of the Wernerian view of the Earth.
A principal focus of Neptunism that provoked immediate controversy involved the origin of basalt. Basalts formed as sills, were differentiated from surface lava flows, the two were not recognized as the same rock type by Werner and his students during this period. Lavas and volcanoes of igneous origin were treated as recent phenomena unrelated to the universal ocean that formed the layers of the Earth. Werner believed. Burning melted overlying basalts and wackes, producing basalts and lavas at low elevations. Basalt
Basalt
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows. By definition, basalt is an aphanitic igneous rock with 45–53% silica and less than 10% feldspathoid by volume, where at least 65% of the rock is feldspar in the form of plagioclase; this is as per definition of the International Union of Geological Sciences classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaiʻi. Basalt features a fine-grained or glassy matrix interspersed with visible mineral grains.
The average density is 3.0 g/cm3. Basalt is defined by its mineral content and texture, physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is grey to black in colour, but weathers to brown or rust-red due to oxidation of its mafic minerals into hematite and other iron oxides and hydroxides. Although characterized as "dark", basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured, superficially resembling andesite to untrained eyes. Basalt has a fine-grained mineral texture due to the molten rock cooling too for large mineral crystals to grow; these phenocrysts are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a vesicular texture is called vesicular basalt, when the bulk of the rock is solid; this texture forms when dissolved gases come out of solution and form bubbles as the magma decompresses as it reaches the surface, yet are trapped as the erupted lava hardens before the gases can escape.
The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic groundmass are referred to as diabase or, when more coarse-grained, as gabbro. Gabbro is marketed commercially as "black granite." In the Hadean and early Proterozoic eras of Earth's history, the chemistry of erupted magmas was different from today's, due to immature crustal and asthenosphere differentiation. These ultramafic volcanic rocks, with silica contents below 45% are classified as komatiites; the word "basalt" is derived from Late Latin basaltes, a misspelling of Latin basanites "very hard stone", imported from Ancient Greek βασανίτης, from βάσανος and originated in Egyptian bauhun "slate". The modern petrological term basalt describing a particular composition of lava-derived rock originates from its use by Georgius Agricola in 1556 in his famous work of mining and mineralogy De re metallica, libri XII. Agricola applied "basalt" to the volcanic black rock of the Schloßberg at Stolpen, believing it to be the same as the "very hard stone" described by Pliny the Elder in Naturalis Historiae.
Tholeiitic basalt is rich in silica and poor in sodium. Included in this category are most basalts of the ocean floor, most large oceanic islands, continental flood basalts such as the Columbia River Plateau. High and low titanium basalts. Basalt rocks are in some cases classified after their titanium content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and the Emeishan Traps. Mid-ocean ridge basalt is a tholeiitic basalt erupted only at ocean ridges and is characteristically low in incompatible elements. E-MORB, enriched MORB N-MORB, normal MORB D-MORB, depleted MORB High-alumina basalt may be silica-undersaturated or -oversaturated, it has greater than 17% alumina and is intermediate in composition between tholeiitic basalt and alkali basalt. Alkali basalt is poor in silica and rich in sodium, it may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a high-magnesium form of basalt, erupted in back-arc basins, distinguished by its low titanium content and trace-element composition.
Ocean island basalt Lunar basalt The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene. Olivine can be a significant constituent. Accessory minerals present in minor amounts include iron oxides and iron-titanium oxides, such as magnetite and ilmenite; because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, paleomagnetic studies have made extensive use of basalt. In tholeiitic basalt and calcium-rich plagioclase are common phenocryst minerals. Olivine may be a phenocryst, when
Ancient Rome
In historiography, ancient Rome is Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom, Roman Republic and Roman Empire until the fall of the western empire. The civilization began as an Italic settlement in the Italian Peninsula, conventionally founded in 753 BC, that grew into the city of Rome and which subsequently gave its name to the empire over which it ruled and to the widespread civilisation the empire developed; the Roman Empire expanded to become one of the largest empires in the ancient world, though still ruled from the city, with an estimated 50 to 90 million inhabitants and covering 5.0 million square kilometres at its height in AD 117. In its many centuries of existence, the Roman state evolved from a monarchy to a classical republic and to an autocratic semi-elective empire. Through conquest and assimilation, it dominated the North African coast and most of Western Europe, the Balkans and much of the Middle East.
It is grouped into classical antiquity together with ancient Greece, their similar cultures and societies are known as the Greco-Roman world. Ancient Roman civilisation has contributed to modern language, society, law, government, art, literature and engineering. Rome professionalised and expanded its military and created a system of government called res publica, the inspiration for modern republics such as the United States and France, it achieved impressive technological and architectural feats, such as the construction of an extensive system of aqueducts and roads, as well as the construction of large monuments and public facilities. The Punic Wars with Carthage were decisive in establishing Rome as a world power. In this series of wars Rome gained control of the strategic islands of Corsica and Sicily. By the end of the Republic, Rome had conquered the lands around the Mediterranean and beyond: its domain extended from the Atlantic to Arabia and from the mouth of the Rhine to North Africa.
The Roman Empire emerged with the dictatorship of Augustus Caesar. 721 years of Roman–Persian Wars started in 92 BC with their first war against Parthia. It would become the longest conflict in human history, have major lasting effects and consequences for both empires. Under Trajan, the Empire reached its territorial peak, it stretched from the entire Mediterranean Basin to the beaches of the North Sea in the north, to the shores of the Red and Caspian Seas in the East. Republican mores and traditions started to decline during the imperial period, with civil wars becoming a prelude common to the rise of a new emperor. Splinter states, such as the Palmyrene Empire, would temporarily divide the Empire during the crisis of the 3rd century. Plagued by internal instability and attacked by various migrating peoples, the western part of the empire broke up into independent "barbarian" kingdoms in the 5th century; this splintering is a landmark historians use to divide the ancient period of universal history from the pre-medieval "Dark Ages" of Europe.
The eastern part of the empire endured through the 5th century and remained a power throughout the "Dark Ages" and medieval times until its fall in 1453 AD. Although the citizens of the empire made no distinction, the empire is most referred to as the "Byzantine Empire" by modern historians during the Middle Ages to differentiate between the state of antiquity and the nation it grew into. According to the founding myth of Rome, the city was founded on 21 April 753 BC on the banks of the river Tiber in central Italy, by the twin brothers Romulus and Remus, who descended from the Trojan prince Aeneas, who were grandsons of the Latin King Numitor of Alba Longa. King Numitor was deposed by his brother, while Numitor's daughter, Rhea Silvia, gave birth to the twins. Since Rhea Silvia had been raped and impregnated by Mars, the Roman god of war, the twins were considered half-divine; the new king, feared Romulus and Remus would take back the throne, so he ordered them to be drowned. A she-wolf saved and raised them, when they were old enough, they returned the throne of Alba Longa to Numitor.
The twins founded their own city, but Romulus killed Remus in a quarrel over the location of the Roman Kingdom, though some sources state the quarrel was about, going to rule or give his name to the city. Romulus became the source of the city's name. In order to attract people to the city, Rome became a sanctuary for the indigent and unwanted; this caused a problem, in that Rome was bereft of women. Romulus visited neighboring towns and tribes and attempted to secure marriage rights, but as Rome was so full of undesirables he was refused. Legend says that the Latins invited the Sabines to a festival and stole their unmarried maidens, leading to the integration of the Latins with the Sabines. Another legend, recorded by Greek historian Dionysius of Halicarnassus, says that Prince Aeneas led a group of Trojans on a sea voyage to found a new Troy, since the original was destroyed at the end of the Trojan War. After a long time in rough seas, they landed on the banks of the Tiber River. Not long after they landed, the men wanted to take to the sea again, but the women who were traveling with them did not want to leave.
One woman, named Roma, suggested that the women burn the ships out at sea to prevent their leaving
Precipitation (chemistry)
Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the'precipitate'; the chemical that causes the solid to form is called the'precipitant'. Without sufficient force of gravity to bring the solid particles together, the precipitate remains in suspension. After sedimentation when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a'pellet'. Precipitation can be used as a medium; the precipitate-free liquid remaining above the solid is called the'supernate' or'supernatant'. Powders derived from precipitation have historically been known as'flowers'; when the solid appears in the form of cellulose fibers which have been through chemical processing, the process is referred to as regeneration. Sometimes the formation of a precipitate indicates the occurrence of a chemical reaction. If silver nitrate solution is poured into a solution of sodium chloride, a chemical reaction occurs forming a white precipitate of silver chloride.
When potassium iodide solution reacts with lead nitrate solution, a yellow precipitate of lead iodide is formed. Precipitation may occur. Precipitation may occur from a supersaturated solution. In solids, precipitation occurs if the concentration of one solid is above the solubility limit in the host solid, due to e.g. rapid quenching or ion implantation, the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is used to synthesize nanoclusters. An important stage of the precipitation process is the onset of nucleation; the creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative surface energy of the solid and the solution. If this energy is not available, no suitable nucleation surface is available, supersaturation occurs. Precipitation reactions can be used for making pigments, removing salts from water in water treatment, in classical qualitative inorganic analysis.
Precipitation is useful to isolate the products of a reaction during workup. Ideally, the product of the reaction is insoluble in the reaction solvent. Thus, it precipitates. An example of this would be the synthesis of porphyrins in refluxing propionic acid. By cooling the reaction mixture to room temperature, crystals of the porphyrin precipitate, are collected by filtration: Precipitation may occur when an antisolvent is added, drastically reducing the solubility of the desired product. Thereafter, the precipitate may be separated by filtration, decanting, or centrifugation. An example would be the synthesis of chromic tetraphenylporphyrin chloride: water is added to the DMF reaction solution, the product precipitates. Precipitation is useful in purifying products: crude bmim-Cl is taken up in acetonitrile, dropped into ethyl acetate, where it precipitates. Another important application of an antisolvent is in ethanol precipitation of DNA. In metallurgy, precipitation from a solid solution is a useful way to strengthen alloys.
An example of a precipitation reaction: Aqueous silver nitrate is added to a solution containing potassium chloride, the precipitation of a white solid, silver chloride, is observed. AgNO 3 + KCl ⟶ AgCl ↓ + KNO 3 The silver chloride has formed a solid, observed as a precipitate; this reaction can be written emphasizing the dissociated ions in a combined solution. This is known as the ionic equation. Ag + + NO 3 − + K + + Cl − ⟶ AgCl ↓ + K + + NO 3 − A final way to represent a precipitate reaction is known as a net ionic reaction. Many compounds containing metal ions produce precipitates with distinctive colors; the following are typical colors for various metals. However, many of these compounds can produce colors different from those listed. Other compounds form white precipitates. Precipitate formation is useful in the detection of the type of cation in a salt. To do this, an alkali first reacts with the unknown salt to produce a precipitate, the hydroxide of the unknown salt. To identify the cation, the color of the precipitate and its solubility in excess are noted.
Similar processes are used in sequence – for example, a barium nitrate solution will react with sulfate ions to form a solid barium sulfate precipitate, indicating that it is that sulfate ions are present. Digestion, or precipitate ageing, happens when a freshly formed precipitate is left at a higher temperature, in the solution from which it precipitates, it results in bigger particles. The physico-chemical process underlying digestion is called Ostwald ripening. Coprecipitation Salting in Salting out Effervescence Zumdahl, Steven S.. Chemical Principles. New York: Houghton Mifflin. ISBN 0-618-37206-7. Precipitation reactions of certain cations Digestion Instruments A Thesis on pattern formation in precipitation reactions
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
Charles Lyell
Sir Charles Lyell, 1st Baronet, was a Scottish geologist who popularised the revolutionary work of James Hutton. He is best known as the author of Principles of Geology, which presented uniformitarianism–the idea that the Earth was shaped by the same scientific processes still in operation today–to the broad general public. Principles of Geology challenged theories popularised by Georges Cuvier, which were the most accepted and circulated ideas about geology in Europe at the time, his scientific contributions included an explanation of earthquakes, the theory of gradual "backed up-building" of volcanoes, in stratigraphy the division of the Tertiary period into the Pliocene and Eocene. He coined the currently-used names for geological eras, Palaeozoic and Cenozoic, he incorrectly conjectured that icebergs may be the emphasis behind the transport of glacial erratics, that silty loess deposits might have settled out of flood waters. Lyell, following deistic traditions, favoured an indefinitely long age for the earth, despite geological evidence suggesting an old but finite age.
He was a close friend of Charles Darwin, contributed to Darwin's thinking on the processes involved in evolution. He helped to arrange the simultaneous publication in 1858 of papers by Darwin and Alfred Russel Wallace on natural selection, despite his personal religious qualms about the theory, he published evidence from geology of the time man had existed on Earth. Lyell was born into a wealthy family, on 14 November 1797, at the family's estate house, Kinnordy House, near Kirriemuir in Forfarshire, he was the eldest of ten children. Lyell's father named Charles Lyell, was noted as a translator and scholar of Dante. An accomplished botanist, it was he who first exposed his son to the study of nature. Lyell's grandfather Charles Lyell, had made the family fortune supplying the Royal Navy at Montrose, enabling him to buy Kinnordy House; the family seat is located near the Highland Boundary Fault. Round the house, in the strath, is good farmland, but within a short distance to the north-west, on the other side of the fault, are the Grampian Mountains in the Highlands.
His family's second country home was in a different geological and ecological area: he spent much of his childhood at Bartley Lodge in the New Forest, in Hampshire in southern England. Lyell entered Exeter College, Oxford, in 1816, attended William Buckland's lectures, he graduated with a BA Hons. Second class degree in classics, in December 1819, gained his M. A. 1821. After graduation he took up law as a profession, entering Lincoln's Inn in 1820, he completed a circuit through rural England. In 1821 he attended Robert Jameson's lectures in Edinburgh, visited Gideon Mantell at Lewes, in Sussex. In 1823 he was elected joint secretary of the Geological Society; as his eyesight began to deteriorate, he turned to geology as a full-time profession. His first paper, "On a recent formation of freshwater limestone in Forfarshire", was presented in 1822. By 1827, he had abandoned law and embarked on a geological career that would result in fame and the general acceptance of uniformitarianism, a working out of the ideas proposed by James Hutton a few decades earlier.
In 1832, Lyell married Mary Horner in Bonn, daughter of Leonard Horner associated with the Geological Society of London. The new couple spent their honeymoon in Italy on a geological tour of the area. During the 1840s, Lyell travelled to the United States and Canada, wrote two popular travel-and-geology books: Travels in North America and A Second Visit to the United States. After the Great Chicago Fire, Lyell was one of the first to donate books to help found the Chicago Public Library. In 1866, he was elected a foreign member of the Royal Swedish Academy of Sciences. Lyell's wife died in 1873, two years Lyell himself died as he was revising the twelfth edition of Principles, he is buried in Westminster Abbey. Lyell was knighted in 1848, in 1864, made a baronet, an hereditary honour, he was awarded the Copley Medal of the Royal Society in 1858 and the Wollaston Medal of the Geological Society in 1866. Mount Lyell, the highest peak in Yosemite National Park, is named after him. In Southwest Nelson in the South Island of New Zealand, the Lyell Range, Lyell River and the gold mining town of Lyell were all named after Lyell.
The jawless fish Cephalaspis lyelli, from the Old Red Sandstone of southern Scotland, was named by Louis Agassiz in honour of Lyell. Lyell had private means, earned further income as an author, he came from a prosperous family, worked as a lawyer in the 1820s, held the post of Professor of Geology at King's College London in the 1830s. From 1830 onward his books provided both fame; each of his three major books was a work continually in progress. All three went through multiple editions during his lifetime, although many of his friends thought the first edition of the Principles was the best written. Lyell used each edition to incorporate additional material, rearrange existing material, revisit old conclusions in light of new evidence. Principles of Geology, Lyell's first book, was his most famous, most influential, most important. First published in three volumes in 1830–33, it established Lyell's credentials as an important geological theorist and pr
Mineral
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
