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Igneous Rock

Igneous rock

Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. The word "igneous" is derived from the Latin ignis, meaning "fire".

Magma origination

The Earth's crust is about 500 kilometers (22 miles) thick under the continents, but averages only some 7 kilometers (4.3 miles) beneath the oceans. It is made up of rocks which have a relatively low density, and beneath the crust there is the denser rock of the mantle, which extends to a depth of nearly 3,000 kilometers (1,860 miles). Most of the magma which forms igneous rocks is generated within the upper parts of the mantle at temperatures estimated between 600 to 1600 °C. This magma, when burned will create diamonds, and possibly pearls! Oysters eat this magma, and get pearls! As magma cools, minerals crystallize from the melt at different temperatures (fractional crystallization). There are relatively few minerals which are important in the formation of igneous rocks. This is because the magma from which the minerals crystallize is rich in only certain elements: silicon, oxygen, aluminium, sodium, potassium, calcium, iron, and magnesium. These are the elements which combine to form the silicate minerals, which account for over ninety percent of all igneous rocks. Igneous rocks make up approximately ninety five percent of the upper part of the Earth's crust, but their great abundance is hidden on the Earth's surface by a relatively thin but widespread layer of sedimentary and metamorphic rocks. Igneous rock are geologically important because:
- their minerals and global chemistry gives information about the composition of the mantle, from where some igneous rocks are extracted, and the temperature and pressure conditions that allowed this extraction, and/or of other pre-existing rock that melted;
- their absolute ages can be obtained from various forms of radiometric dating and thus can be compared to adjacent geological strata, allowing a time sequence of events;
- their features are usually characteristic of a specific tectonic environment, allowing tectonic reconstitutions (see plate tectonics);
- in some special circumstances they host important mineral deposits (ores): for example, tungsten, tin, and uranium, are commonly associated with granites.

Classification

Igneous rocks are classified according to mode of occurrence, texture, chemical composition, and the geometry of the igneous body.

Mode of occurrence

In terms of modes of occurrence, igneous rocks can be either intrusive (plutonic) or extrusive (volcanic). Intrusive igneous rocks crystallize within the crust interior. Intrusive igneous rocks (also called plutonic rocks, named after Pluto, the Roman god of the underworld) are formed from magma that cools and hardens within the earth. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. The mineral grains in such rocks can generally be identified with the naked eye. The central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores (called batholiths) may occupy huge areas of the surface. Coarse grained intrusive igneous rocks which form at depth within the earth are termed as abyssal; intrusive igneous rocks which form near the surface are termed hypabyssal. Extrusive igneous rocks are the result of volcanic eruptions and, therefore, solidify in atmospheric conditions. Extrusive igneous rocks (also called volcanic rocks, named after Vulcan, the Roman name for the god of fire) are formed at the Earth's surface as a result of volcanic activity. The temperatures only a few kilometers beneath the surface of the earth are higher than the temperatures at which most rocks would melt at the surface. These rocks remain solid, however, due to the pressure exerted by the overlying rocks. If the rocks fracture the pressure may be released and a sizeable volume of rock will melt. The resulting magma will be forced up through the fractures to the surface, forming a volcano. Molten or partly molten rock (called lava) will flow from the volcano and spread out. Because lava cools and crystallizes rapidly, it is fine grained. If the cooling has been so rapid as to prevent the formation of even small crystals the resulting rock may be a glass (such as the rock obsidian). Because of this fine grained texture it is much more difficult to distinguish between the different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a microscope, so only an approximate classification can usually be made in the field. Material may be violently forced out of the volcano during igneous activity as blocks of rock, pellets, and ash. This material is called pyroclastic rock (also called fragmented igneous rock) and may fall nearby, forming part of the volcano itself, or may be spread over great distances by the wind. The classification of the many types of different igneous rocks can provide us with important information about the conditions under which they formed. Two important variables used for the classification of igneous rocks are particle size, which largely depends upon the cooling history, and the mineral composition of the rock. Feldspars, quartz, olivines, pyroxenes, amphiboles, and micas are all important minerals in the formation of igneous rocks, and they are basic to the classification of these rocks. All other minerals present are regarded as nonessential (called accessory minerals). In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of quartz, and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present. Igneous rocks which have crystals large enough to be seen by the naked eye are called phaneritic; those with crystals too small to be seen are called aphanitic. Generally speaking, phaneritic implies an intrusive origin; aphanitic an extrusive one. The crystals embedded in fine grained igneous rocks are termed porphyritic. The porphyritic texture develops when some of the crystals grow to considerable size before the main mass of the magma consolidates into the finer grained uniform material.

Texture

The most important distinction in igneous rocks is texture, which is the physical character of the rock, including the size, shape, orientation, and distribution of grains and the intergrain relationships.

Grain size

According to the size of the grains, igneous rocks may be classified as pegmatic (very large grains), phaneritic (only large grains), porphyritic (some large grains and some small grains), aphanitic (only small grains), vesicular (voids caused by trapped gas while cooling), glassy (no grains), or pyroclastic (fragments ejected in a volcanic eruption).
- Phaneritic rocks contain minerals with grains (crystals) visible to the unaided eye and are commonly intrusive (as the slower cooling rates allow the formation of large crystals). In the extreme, such rocks may contain extremely large crystals, in which case they are termed pegmatitic.
- In extrusive rocks, where cooling is much more rapid, the individual mineral crystals are usually not visible and these rocks are termed aphanitic.
- Porphyritic textures are an intermediate situation between the previous two: the groundmass of the rock has an aphanitic texture, but crystals (termed in this particular occurrence as phenocrysts) are visible to the unaided eye.
- If a molten magma cools at extremely high rates, allowing no crystallization, the result is a volcanic glass called obsidian.

Crystal shapes

Crystal shape is also an important factor in the texture of an igneous rock. Crystals may be euhedral, subeuhedral or anhedral:
- Euhedral, if the crystallographic shape is preserved.
- Subeuhedral, if only part is preserved.
- Anhedral, if the crystal presents no recognizable crystallographic direction.

Chemical - mineralogical composition

Igneous rocks can be subdivided according to two main chemical/mineralogical parameters: Chemical - Total alkali - silica content (TAS diagram) for volcanic rock classification used when modal or mineralogic data is unavailable:
- acid igneous rocks containing a high silica content, greater than 63% SiO₂ (examples rhyolite and dacite)
- intermediate igneous rocks containing between 52 - 63% SiO₂ (example andesite)
- basic igneous rocks have low silica 45 - 52% and typically high iron - magnesium content (example basalt)
- ultrabasic igneous rocks with less than 45% silica. (examples picrite and komatiite)
- alkalic igneous rocks with 5 - 15% alkali (K₂O + Na₂O) content (examples phonolite and trachyte) :Note: the acid-basic terminology is used more broadly in older geological literature. Mineralogic contents - felsic versus mafic:
- felsic rock, with predominance of quartz, alkali feldspar and/or feldspathoids: the felsic minerals; these rocks (e.g., granite) are usually light coloured, and have low density.
- mafic rock, with predominance of mafic minerals pyroxenes, olivines and calcic plagioclase; these rocks (example, basalt) are usually dark coloured, and have higher density than felsic rocks.
- ultramafic rock, with more than 90% of mafic minerals (e.g., dunite) The following table is a simple subdivision of igneous rocks according both to their composition and mode of occurrence. For a more detailed classification see QAPF diagram.

Geometry of the igneous body

Igneous rocks can also classified according to the shape and size of the intrusive body and its relation to the other formations into which it intrudes. Typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. The extrusive types usually are called lavas.

Example of classification

Granite is an igneous, intrusive rock (crystallized at depth), with felsic composition (rich in silica and with more than 10% of felsic minerals) and phaneritic, subeuedral texture (minerals are visible for the unaided eye and some of them retain original crystallographic shapes). Granite is the most abundant intrusive rock that can be found in the continents.

Reference

- Le Maitre, L.E., ed., (2002) Igneous Rocks: A Classification and Glossary of Terms 2nd edition, Cambridge.

External links

- [http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Notes/igneous_rocks.html USGS Igneous Rocks] Category:Petrology Category:Igneous rocks Category:Volcanology ko:화성암 ja:火成岩 th:หินอัคนี

Rock (geology)

, plutonic, metamorphic rock types of North America. ]] Rock is a naturally occurring aggregate of minerals and/or mineraloids. Rocks are classified by mineral and chemical composition; the texture of the constituent particles; and also by the processes that formed them. These indicators separate rocks into igneous, sedimentary, and metamorphic. Igneous rocks are formed from molten magma, and are divided into two main categories: Plutonic rock and Volcanic rock. Plutonic rocks result when the magma cools and crystallises slowly within the Earth's crust, while Volcanic rocks result from the magma reaching the surface either as lava or fragmental ejecta. Sedimentary rocks are formed by deposition of either detrital or organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation. The latter can occur at or near the earth's surface, especially in the case of carbonate-rich sediments. Metamorphic rocks are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the earth's surface, and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation). The transformation of one rock type to another is described by the geological model called the rock cycle. The Earth's crust (including the lithosphere) and mantle are formed of rock.

External links

- [http://www.geol.lsu.edu/henry/Geology3041/2IgneousClassify/IgneousClassFlow.htm Classification of Igneous Rocks] Category:Geology Category:Rocks ja:岩石 ms:Batu th:หิน

Magma

:This article is about the type of molten rock. For other meanings of magma, see Magma (disambiguation). Magma is molten rock often located inside a magma chamber beneath the surface of the Earth. Magma is a complex high-temperature silicate solution that is ancestral to all igneous rocks. It is capable of intrusion into adjacent crustal rocks or extrusion onto the surface. Magma exists between 650 and 1200 °C. Magma is under high pressure and sometimes emerges through volcanic vents in the form of flowing lava (melt as it exists above the Earth's surface) and pyroclastic ejecta. These products of a volcanic eruption usually contain liquids, crystals and dissolved gases which have never before reached the planet's surface. Magma collects in many separate magma chambers within the Earth's crust, and will have slightly different compositions in different places, which can occur at either a subduction zone, a rift zone or mid-oceanic ridge, or above a mantle plume hotspot. Magma's formation only takes place under specific conditions in the Earth's asthenosphere.

Formation

A sudden decrease in pressure can cause what is known as decompression melting. This may occur due to tectonic adjustments or as molten rock displaces and fractures adjacent rock during its rise to a shallow depth in the Earth's crust. The geothermal gradient averages about 25°C/km with a wide range from a low of 5-10°C/km within oceanic trenches and subduction zones to 30-50°C/km under mid-ocean ridges and volcanic arc environments. A combination of high temperature and low pressure near surface environments are most conducive to melting due to pressure reduction. Magma can also be formed due to the addition of volatiles to heated rock. Volatiles (water and gases) are released from a descending slab of oceanic crust as it is subducted, these volatiles move into the overlying crustal material and initiate melting. Volatiles can break up the mineral bonds within the melting rock and cause its melting point to decrease, allowing for magma formation. Magma formation also results due to the melting of crustal rock by pre-existing magma whose temperature is so great that it melts the crust as it rises, creating even more magma. Magma rises primarily because a melt is less dense than its source rock, it is propelled upward through the lithosphere by the buoyancy that its lower density creates (the way less dense wood is pushed up and floats in denser water). This results in the formation of magma chambers and eventually volcanoes, magma being pushed all the way to the Earth's surface results in a volcanic eruption.

Composition

The composition of magma will change depending on the make-up of the overlying rocks that it melts as it penetrates the Earth's crust to erupt in the form of lava. There are three basic types of magma: mafic, andesitic (or intermediate), and felsic. Magma is composed mainly of silica; alkalis (sodium, potassium, calcium, magnesium) and iron. Generally speaking, the more mafic the magma is, the gentler the eruption will be. This is because high levels of silica cause volatiles to build-up and can create an explosive eruption which is seen in composite volcanoes. Characteristics of different magmas are as follows: :Mafic (basaltic) ::SiO₂ < 50% ::Fe-Mg ~ 4% ::Temperature: up to 1500°C ::Viscosity: Low ::Eruptive behavior: gentle ::Distribution: divergent plate boundaries, hot spots, convergent plate boundaries; basaltic magma is typically found in areas where oceanic crust is being melted, oceanic crust contains high levels of iron. :Intermediate (andesitic) ::SiO₂ ~ 60% ::Fe-Mg: ~ 3% ::Temperature: ~1000°C ::Viscosity: Intermediate ::Eruptive behavior: explosive ::Distribution: convergent plate boundaries :Felsic (rhyolitic) ::SiO₂ >70% ::Fe-Mg: ~ 2% ::Temp: 700°C ::Viscosity: High ::Eruptive behavior: explosive ::Distribution: hot spots in continental crust (Yellowstone National Park); this type of magma occurs mainly where continental crust, which contains large amounts of silica, is being melted, causing the explosive behavior. Category:Petrology Category:Volcanology ko:마그마 ms:Magma ja:マグマ th:หินหนืด

Intrusion

:Pluton redirects here. For the ancient Roman god, see Pluto. For the French nuclear missile system, see Pluton missile. For the physical act of trespass with a possible intent to steal, see intruder. intruder In geology an intrusion is usually a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Intrusive rocks include all varieties of igneous rocks from coarse-grained, phaneritic granites of large batholiths to very fine grained, aphanitic, rhyolites in volcanic necks or feeder pipes. In composition, intrusive rocks also include the entire sequence of igneous rock types from the dense and dark ultramafic peridotites to the very light-colored and low-density alkali granites and syenites. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto, the Roman god of the underworld. A well-known example of an igneous intrusion is Devil's Tower in Wyoming, USA. USA.]] Intrusive rocks also exist in a wide range of forms from mountain range sized batholiths to thin vein-like fracture fillings of aplite. Structural types include:
- batholith: large irregular intrusions.
- stock: smaller irregular disordant intrusions.
- dike: a relatively narrow tabular discordant body with near vertical attitude.
- sill: a relatively thin tabular concordant body intruded along bedding planes, horizontal attitude.
- pipe or volcanic neck: circular or tube shaped nearly vertical body which may have been a feeder vent for a volcano.
- laccolith: concorant body with essentially flat base and dome shaped upper surface, usually has a feeder pipe below.

Volcanic rock

.]] ).]] Volcanic rock is an igneous rock of volcanic origin. Volcanic rocks are usually fine-grained or aphanitic to glassy in texture. They often contain clasts of other rocks and phenocrysts. Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. They were created during fractional crystallization of magma before extrusion. Rhomb porphyry is an example with large rhomb shaped phenocrysts enbedded in a very fine grained matrix. Volcanic rocks are named according to their chemical composition. Basalt is a very common volcanic rock with low silica content. Rhyolite is a volcanic rock with high silica content. Rhyolite has the same chemical composition as granite and basalt is compositionally equal to gabbro. Intermediate volcanic rocks include andesite, dacite, trachyte and latite. Volcanic rocks often have a vesicular texture, which is the result voids left by volatiles escaping from the molten lava. Pumice is a rock, which is an example of explosive volcanic eruption. It is so vesicular that it floats in water. Pyroclastic rocks are the product of explosive volcanism. They are usually felsic (high in silica). Examples of pyroclastic rocks are tuff and ignimbrite. Shallow intrusions, which possess structure similar to volcanic rather than plutonic rocks are also considered to be volcanic.

Mantle (geology)

to exosphere. Partially to scale.]] exosphere waves.]] The Earth's mantle is the layer in the structure of the Earth that lies directly under the Earth's crust and above the Earth's outer core. The term is also applied to the structure of other planets. Earth's mantle lies roughly between 30 and 2,900 km below the surface. The boundary between the crust and the mantle is the Mohorovičić discontinuity, named for its discoverer, and is usually called the Moho. The Moho is a boundary at which there is a sudden change in the speed of seismic waves. At one time some thought that the Moho was the structure at which the earth's rigid crust moved relative to the mantle. Current research places this zone of movement within the mantle, from 70 km (43 mi) below the ocean crust to 150 km (93 mi) below the continental crust. The mantle just below the crust is composed of cold and therefore rigid mantle fused to the crust but at the same time separated from it by the Moho. This rigid layer of crust and the upper mantle forms the lithosphere. The mantle differs substantially from the crust in its mechanical characteristics and its chemical composition. It is chiefly the difference of chemistry on which the distinction between crust and mantle is based. Mantle rock consists of olivines, different pyroxenes and other mafic minerals. Typified by peridotite, dunite, and eclogite, mantle rocks also possesses a higher portion of iron and magnesium and a smaller portion of silicon and aluminium than the crust. In the mantle, temperatures range between 100°C at the upper boundary to over 3,500°C at the boundary with the core. Although these temperatures far exceed the melting points of the mantle rocks at the surface, particularly in deeper ranges, they are almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents them from melting. The subregion of the mantle extending about 250 km (155 mi) below the lithosphere is called the asthenosphere. It some regions of the earth, this subregion of the mantle is associated with a region of the mantle that passes seismic waves more slowly. This region is called the low-velocity zone. The cause of this low velocity zone is still debated. Currently theories include the influence of temperature and pressure or the existence of a small amount of partial melt. Due to the temperature difference between the Earth's crust and outer core there is a convective material circulation in the mantle. Hot material ascends as a plutonic diapir from the border with the outer core, while cooler (and heavier) material sinks downward. This is often in the form of large-scale lithospheric downwellings at plate boundaries called subduction zones. During the ascent the material of the mantle cools down adiabatically. The temperature of the material falls with the pressure relief connected with the ascent, and its heat distributes itself over a larger volume. Near the lithosphere the pressure relief can lead to partial melting of the diapir, leading to volcanism and plutonism. The convection of the Earth's mantle is a chaotic process (in the sense of fluid dynamics), which is thought to drive the motion of plates. Plate motion should not be confused with the older term continental drift which applies purely to the movement of the crustal components of the continents. The movements of the lithosphere and the underlying mantle are thereby partially decoupled, since due to the rigidity of the lithosphere, a tectonic plate can only move as a whole. Continental drift is therefore only a diffuse image of the movements at the upper limit of the Earth's mantle. The convection of the mantle is not yet clarified in detail. There are different theories, according to which the Earth's mantle is divided into different floors of separate convection. Although there is a tendency to larger viscosity at greater depth, this relation is far from linear, and shows layers with dramatically decreased viscosity, in particular in the upper mantle and at the boundary with the core [http://www2.uni-jena.de/chemie/geowiss/geodyn/poster2.html]. Due to the low viscosity in the upper mantle one could reason that there should be no earthquakes below approximately 300 km depth. However, in subduction zones, the geothermal gradient can be lowered, increasing the strength of the surrounding mantle, and allowing earthquakes to occur down to a depth of 400 km and 670 km. The pressure at the bottom of the mantle is ~140 GPa (1.4 Matm). There exists increasing pressure as one travels deeper into the mantle, the entire mantle, however, is still thought to deform like a fluid on long timescales. The viscosity of the upper mantle ranges between 10²¹ and 10²⁴ Pa·s, depending on depth [http://www2.uni-jena.de/chemie/geowiss/geodyn/poster2.html]. Thus, the upper mantle can only flow very slowly. Why is the inner core thought solid, the outer core thought liquid, and the mantle solid/plastic? The melting points of iron rich substances are higher than pure iron. The core is composed almost entirely of pure iron, while iron rich substances are more common outside the core. So, surface iron-substances are solid, upper mantle iron-substances are semi-molten (as it is hot and they are under relatively little pressure), lower mantle iron-substances are solid (as they are under tremendous pressure), outer core pure iron is liquid as it has a very low melting point (despite enormous pressure), and the inner core is solid due to the overwhelming pressure found at the centre of the planet. Category:Geology Category:Geophysics Category:Planetary science ja:マントル th:เนื้อโลก

Latin

Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. It gained great importance as the formal language of the Roman Empire. All Romance languages, those being most notably Spanish, French, Portuguese, Italian, and Romanian, are descended from Latin, and many words based on Latin are found in other modern languages such as English. The Latin alphabet, derived from the Greek, remains the most widely-used alphabet in the world. It is said that 80 percent of scholarly English words are derived from Latin (in a large number of cases by way of French). Moreover, in the Western world, Latin was a lingua franca, the learned language for scientific and political affairs, for more than a thousand years, being eventually replaced by French in the 18th century and English in the late 19th. Ecclesiastical Latin remains the formal language of the Roman Catholic Church to this day, and thus the official national language of the Vatican. The Church used Latin as its primary liturgical language until the Second Vatican Council in the 1960s. Latin is also still used (drawing heavily on Greek roots) to furnish the names used in the scientific classification of living things. The modern study of Latin, along with Greek, is known as Classics.

Main features

Latin is a synthetic inflectional language: affixes (which usually encode more than one grammatical category) are attached to fixed stems to express gender, number, and case in adjectives, nouns, and pronouns, which is called declension; and person, number, tense, voice, mood, and aspect in verbs, which is called conjugation. There are five declensions (declinationes) of nouns and four conjugations of verbs. There are six noun cases: #nominative (used as the subject of the verb or the predicate nominative), #genitive (used to indicate relation or possession, often represented by the English of or the addition of s to a noun), #dative (used of the indirect object of the verb, often represented by the English to or for), #accusative (used of the direct object of the verb, or object of the preposition in some cases), #ablative (separation, source, cause, or instrument, often represented by the English by, with, from), #vocative (used of the person or thing being addressed). In addition, some nouns have a locative case used to express location (otherwise expressed by the ablative with a preposition such as in), but this survival from Proto-Indo-European is found only in the names of lakes, cities, towns, small islands, and a few other words related to locations, such as "house", "ground", and "countryside". Latin itself, being a very old language, is far closer to Proto-Indo-European than are most modern Western European languages; it has, in fact, about the same relationship with PIE as modern Italian or French has to Latin. There are six general tenses in Latin (technically they are tense/aspect/mood complexes). The indicative mood can be used with all of them. The subjunctive mood, however, has only present, imperfect, perfect, and pluperfect tenses. These tenses in the subjunctive mood do not completely correlate in meaning to the tenses in the indicative. The following examples are of the first conjugation verb "laudare" ("to praise") in the indicative mood and the active voice:
Primary sequence tenses
# present (laudo, "I praise") # imperfect (laudabam, "I was praising") # future (laudabo, "I shall praise," "I will praise")
Secondary sequence tenses
# perfect (laudavi, "I praised", "I have praised") # pluperfect (laudaveram, "I had praised") # future perfect (laudavero, "I shall have praised," "I will have praised") The future perfect tense can also imply a normal future idea (like in "When I will have run...") and so may also sometimes be included in the primary sequence.
Latin and Romance
After the collapse of the Roman Empire, Latin evolved into the various Romance languages. These were for many centuries only spoken languages, Latin still being used for writing. For example, Latin was the official language of Portugal until 1296 when it was replaced by Portuguese. The Romance languages evolved from Vulgar Latin, the spoken language of common usage, which in turn evolved from an older speech which also produced the formal classical standard. Latin and Romance differ (for example) in that Romance had distinctive stress, whereas Latin had distinctive length of vowels. In Italian and Sardo logudorese, there is distinctive length of consonants and stress, in Spanish only distinctive stress, and in French even stress is no longer distinctive. Another major distinction between Romance and Latin is that all Romance languages, excluding Romanian, have lost their case endings in most words except for some pronouns. Romanian retains a direct case (nominative/accusative), an indirect case (dative/genitive), and vocative. In Italy, Latin is still compulsory in secondary schools as Liceo Classico and Liceo Scientifico which are usually attended by people who aim to the highest level of education. In Liceo Classico Ancient Greek is a compulsory subject.
Latin and English
See Latin influence in English for a more complete exposition. English grammar is independent of Latin grammar, though prescriptive grammarians in English have been heavily influenced by Latin. Attempts to make English grammar follow Latin rules — such as the prohibition against the split infinitive — have not worked successfully in regular usage. However, as many as half the words in English were derived from Latin, including many words of Greek origin first adopted by the Romans, not to mention the thousands of French, hundreds of Spanish, Portuguese and Italian words of Latin origin that have also enriched English. During the 16th and on through the 18th century English writers created huge numbers of new words from Latin and Greek roots. These words were dubbed "inkhorn" or "inkpot" words (as if they had spilled from a pot of ink). Many of these words were used once by the author and then forgotten, but some remain. Imbibe, extrapolate, dormant and inebriation are all inkhorn terms carved from Latin words. In fact, the word etymology is derived from the Greek word etymologia, meaning "true sense of the word." Latin was once taught in many of the schools in Britain with academic leanings - perhaps 25% of the total [http://www.channel4.com/history/microsites/T/teachem2/thennow/]. However, the requirement for it was gradually abandoned in the professions such as the law and medicine, and then, from around the late 1960s, for admission to university. After the introduction of the Modern Language GCSE in the 1980s, it was gradually replaced by other languages, although it is now being taught by more schools along with other classical languages.
Latin education
The linguistic element of Latin courses offered in high schools or secondary schools, and in universities, is primarily geared toward an ability to translate Latin texts into modern languages, rather than using it in oral communication. As such, the skill of reading is heavily emphasized, whereas speaking and listening skills are barely touched upon. However, there is a growing movement, sometimes known as the Living Latin movement, whose supporters believe that Latin can, or should, be taught in the same way that modern "living" languages are taught, that is, as a means of both spoken and written communication. One of the most interesting aspects of such an approach is that it assists speculative insight into how many of the ancient authors spoke and incorporated sounds of the language stylistically; without understanding how the language is meant to be heard it is very difficult to identify patterns in Latin poetry. Institutions offering Living Latin instruction include the Vatican and the University of Kentucky. In Britain the Classical Association encourages this approach, and there has been something of a vogue for books describing the adventures of a mouse called Minimus. In the United States there is a thriving competitive organization for high school Latin students, the National Junior Classical League (the second-largest youth organization in the world after the Boy Scouts), backed up by the Senior Classical League for college students. Many would-be international auxiliary languages have been heavily influenced by Latin, and the moderately successful Interlingua considers itself to be the modernized and simplified version of the language (le latino moderne international e simplificate). Latin translations of modern literature such as Paddington Bear, Winnie the Pooh, Harry Potter and the Philosopher's Stone, Le Petit Prince, Max und Moritz, and The Cat in the Hat have also helped boost interest in the language.
See also

About the Latin language

- Latin grammar
- Latin spelling and pronunciation
- Latin declension
- Latin conjugation
- Latin alphabet
- List of Latin words with English derivatives
- Latin verbs with English derivatives
- Latin nouns with English derivatives
- ablative absolute
- Word order in Latin
About the Latin literary heritage

- Latin literature
- Romance languages
- Loeb Classical Library
- List of Latin phrases
- List of Latin proverbs
- Brocard
- List of Latin and Greek words commonly used in systematic names
- List of Latin place names in Europe
- Carmen Possum
Other related topics

- Roman Empire
- Internationalism
References

- Bennett, Charles E. Latin Grammar (Allyn and Bacon, Chicago, 1908)
- N. Vincent: "Latin", in The Romance Languages, M. Harris and N. Vincent, eds., (Oxford Univ. Press. 1990), ISBN 0195208293
- Waquet, Françoise, Latin, or the Empire of a Sign: From the Sixteenth to the Twentieth Centuries (Verso, 2003) ISBN 1859844022; translated from the French by John Howe.
- Wheelock, Frederic. Latin: An Introduction (Collins, 6th ed., 2005) ISBN 0060784237
External links

- [http://www.jambell.com/latin.html Latin Phrases for after dinner conversation (Thanks to Elaine Poole)]
- [http://www.ethnologue.com/show_language.asp?code=lat Ethnologue report for Latin]
- [http://forumromanum.org/literature/index.html Corpus Scriptorum Latinorum] is a comprehensive webography of Latin texts and their translations.
- [http://www.perseus.tufts.edu/ The Perseus Project] has many useful pages for the study of classical languages and literatures, including [http://www.perseus.tufts.edu/cgi-bin/resolveform?lang=Latin an interactive Latin dictionary].
- [http://lysy2.archives.nd.edu/cgi-bin/words.exe words by William whitaker] is a dictionary program online capable of looking up various word forms.
- [http://retiarius.org/ Retiarius.Org] includes a Latin text search engine.
- [http://www.nd.edu/~archives/latgramm.htm Latin-English dictionary and Latin grammar from U of Notre Dame]
- [http://latin-language.co.uk/ Latin language] History of Latin language, Latin texts with English translation and a collection of dictionaries.
- [http://augustinus.eresmas.net/scl/ Societas Circulorum Latinorum] gathers together Latin Circles all over the world.
- [http://www.learnlatin.tk LearnLatin.tk] - Free online course in Latin
- [http://www.latintests.net/ LatinTests.net] - Lets Latin learners test their grammar and vocabulary with self-checking quizzes.
- [http://thelatinlibrary.com/ The Latin Library] contains many Latin etexts
- [http://www.textkit.com/ Textkit] has Latin textbooks and etexts.
- [http://www.websters-online-dictionary.org/definition/Latin-english/ Latin–English Dictionary]: from Webster's Rosetta Edition.
- [http://www.language-reference.com/ Language reference] Cross-foreign-language lexicon powered by its own search engine. All cross combinations between Latin and French, German, Italian, Spanish.
- [http://comp.uark.edu/~mreynold/rhetor.html Rhetor by Gabriel Harvey] was originally published in 1577 and never again reprinted.
- [http://freewebs.com/omniamundamundis omniamundamundis] Latin hypertexts from fourteen ancient Roman authors.
- [http://www.saltspring.com/capewest/pron.htm Pronunciation of Biological Latin, Including Taxonomic Names of Plants and Animals]
- [http://www.yleradio1.fi/nuntii Nuntii Latini (News in Latin)], written and spoken (RealAudio) news in latin. Weekly review of world news in Classical Latin, the only international broadcast of its kind in the world, produced by YLE, the Finnish Broadcasting Company.
- [http://www.tranexp.com:2000/InterTran?url=http%3A%2F%2F&type=text&text=Replace%20Me&from=eng&to=ltt InterTran Latin], Translate from Latin to ENGLISH or vice versa.
- [http://www.latinvulgate.com Latin Vulgate] The Latin and English of the Old & New Testaments in parallel, along with the Complete Sayings of Jesus in parallel Latin and English. Category:Classical languages Category:Ancient languages Category:Fusional languages Category:Languages of Italy Category:Languages of Vatican City als:Latein zh-min-nan:Latin-gí ko:라틴어 ja:ラテン語 simple:Latin language th:ภาษาละติน

Continental crust

The continental crust is the layer of granitic and sedimentary rock which forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. It is less dense and more rigid than the material of the Earth's mantle and thus "floats" on top of it. Continental crust is also less dense than oceanic crust, though it is considerably thicker, averaging 20 to 80 km versus the average oceanic thickness of around 5-10 km. As a consequence, when active margins of continental crust meet oceanic crust in subduction zones, the oceanic crust is subducted. Its relative low density keeps the continental crust from being subducted or re-cycled back into the mantle. For this reason the oldest rocks on Earth are within the "cratons" or cores of the continents, rather than in repeatedly recycled oceanic crust. Continental crust is thickest beneath mountain ranges with a deep root. This fact results from the isostatic uplift associated with orogeny (mountain formation). As it is still being formed today, the amount of continental crust has been increasing over geological time. About 40% of the Earth's surface is now underlain by continental crust.

External link

- [http://www.geo.cornell.edu/geology/classes/geochemdata/CrustalAbundances.html Average composition of Continental Crust]
- [http://earth.leeds.ac.uk/assyntgeology/extra_info/ehistory.htm Making new continents] Category:Plate tectonics ko:대륙 지각

Mineral

This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). Minerals are natural compounds formed through geological processes. The term "mineral" encompasses not only the material's chemical composition but also the mineral structures. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms (organic compounds are usually excluded). The study of minerals is called mineralogy. mineralogy]

Mineral definition and classification

To be classified as a "true" mineral, a substance must be a solid and have a crystal structure. It must also be an inorganic, naturally-occurring, homogenous substance with a defined chemical composition. The chemical composition may vary between end members of a mineral system. For example the plagioclase feldspars comprise a continuous series from sodium-rich albite (NaAlSi₃O₈) to calcium-rich anorthite (CaAl₂Si₂O₈) with four recognized intermediate compositions between. Mineral-like substances that don't strictly meet the definition are sometimes classified as mineraloids. Other natural-occurring substances are Nonminerals. Industrial minerals is a commercial term and refers to commercially valuable mined materials (see also Minerals and Rocks section below). A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic lattice arrangements of atoms in three dimensions in the six crystal systems, and all crystal structures currently recognized fit in one of these 14 arrangements. This crystal structure is based on regular internal atomic or ionic arrangement that is often visible as the mineral form. Even when the mineral grains are too small to see or are irregularly shaped the crystal structure can be determined by x-ray analysis and/or optical microscopy. Chemistry and crystal structure define together a mineral. In fact, two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure. Crystal structure greatly influences a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure carbon), graphite is very soft, while diamond is the hardest of all known minerals. There are currently just over 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval of and naming of new mineral species found in nature.

Minerals and rocks

A mineral is a naturally occurring, inorganic substance with a definite chemical composition and a crystalline structure. A rock is an aggregate of one or more minerals. (A rock may also include organic remains.) The specific minerals in a rock can vary a lot. Some minerals, like quartz, mica or feldspar are common, while others have been found in only one or two locations worldwide. Over half of the mineral species known are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains. Commercially valuable minerals and rocks are refered to as industrial minerals.

Physical properties of minerals

Classifying minerals can range from simple to very difficult. A mineral can be identified by several physical properties, some of them being sufficient for full identification without equivocation. In other cases, minerals can only be classified by more complex chemical or X-ray diffraction analysis; these methods, however, can be costly, time-consuming, and even risk damaging the sample. Physical properties commonly used are :
- Crystal structure and habit: See the above discussion of crystal structure. A mineral may show good crystal habit or form, or it may be massive, granular or compact with only microscopically visible crystals.
- Hardness: the physical hardness of a mineral is usually measured according to the Mohs scale of mineral hardness.
- Luster indicates the way a mineral's surface interacts with light and can range from dull to glassy (vitreous).
- Color indicates the appearance of the mineral in reflected light or transmitted light for translucent minerals (i.e. what it looks like to the naked eye).
- Streak refers to the color of the powder a mineral leaves after rubbing it on an unglazed porcelain streak plate.
- Cleavage describes the way a mineral may come apart or cleave in different ways. In thin section, cleavage is visible as thin parallel lines across a mineral.
- Fracture describes how a mineral breaks when broken contrary to its natural cleavage planes.
- Specific gravity relates the mineral mass to the mass of an equal volume of water, namely the density of the material.
- Other properties: fluorescence (response to ultraviolet light), magnetism, radioactivity, tenacity (response to mechanical induced changes of shape or form), and reactivity to dilute acids.

Chemical properties of minerals

Minerals may be classified according to chemical composition. They are here categorized by anion group. The list below is in approximate order of their abundance in the Earth's crust. The list follows the Dana classification system.

Silicate class

The largest group of minerals by far are the silicates, which are composed largely of silicon and oxygen, with the addition of ions such as aluminium, magnesium, iron, and calcium. Some important rock-forming silicates include the feldspars, quartz, olivines, pyroxenes, amphiboles, garnets, and micas.

Carbonate class

The carbonate minerals consist of those minerals containing the anion (CO₃)^2- and include calcite and aragonite (both calcium carbonate), dolomite (magnesium/calcium carbonate) and siderite (iron carbonate). Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor. Carbonates are also found in evaporitic settings (e.g. the Great Salt Lake, Utah) and also in karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites. The carbonate class also includes the nitrate and borate minerals.

Sulfate class

Sulfates all contain the sulfate anion, in the form SO₄^2-. Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface. Sulfates also occur in hydrothermal vein systems as gangue minerals along with sulfide ore minerals. Another occurrence is as secondary oxidation products of original sulfide minerals. Common sulfates include anhydrite (calcium sulfate), celestite (strontium sulfate), barite (barium sulfate), and gypsum (hydrated calcium sulfate). The sulfate class also includes the chromate, molybdate, selenate, sulfite, tellurate, and tungstate minerals.

Halide class

The halides are the group of minerals forming the natural salts and include fluorite (calcium fluoride), halite (sodium chloride), sylvite (potassium chloride), and sal ammoniac (ammonium chloride). Halides, like sulfates, are commonly found in evaporitic settings such as playa lakes and landlocked seas such as the Dead Sea and Great Salt Lake. The halide class includes the fluoride, chloride, and iodide minerals.

Oxide class

Oxides are extremely important in mining as they form many of the ores from which valuable metals can be extracted. They commonly occur as precipitates close to the Earth's surface, oxidation products of other minerals in the near surface weathering zone, and as accessory minerals in igneous rocks of the crust and mantle. Common oxides include hematite (iron oxide), magnetite (iron oxide), chromite (chromium oxide), spinel (magnesium aluminium oxide - a common component of the mantle), rutile (titanium dioxide), and ice (hydrogen oxide). The oxide class includes the oxide and the hydroxide minerals.

Sulfide class

Many sulfides are economically important as metal ores. Common sulfides include pyrite (iron sulfide - commonly known as fools' gold), chalcopyrite (copper iron sulfide) and galena (lead sulfide). The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).

Phosphate class

The phosphate mineral group actually includes any mineral with a tetrahedral unit AO₄ where A can be phosphorus, antimony, arsenic or vanadium. By far the most common phosphate is apatite which is an important biological mineral found in teeth and bones of many animals. The phosphate class includes the phosphate, arsenate, vanadate, and antimonate minerals.

Element class

The Elemental group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulfur). This group also includes natural alloys, such as electrum (a natural alloy of gold and silver), phosphides, silicides, nitrides and carbides (which are usually only found naturally in a few rare meteorites).

External links

- [http://mineral.galleries.com/minerals/by_name.htm Mineral gallery]
- [http://www.minerals.net/index.htm Minerals.net]
- [http://www.mindat.org/index.php mindat.org mineral database]
- [http://webmineral.com Webmineral.com]
- [http://www.minerant.org/databases.html a directory of on-line databases related to mineralogy and crystallography]

References

- [http://volcanoes.usgs.gov/Products/Pglossary/mineral.html Photo glossary of volcano terms from the USGS Volcano Hazards Program] Category:Geology Category:Mineralogy
- ja:鉱物 simple:Mineral th:แร่

Crystallize

:This article is about the form of solid matter. For other uses of this word, see Crystal (disambiguation). Crystal (disambiguation) A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. Generally, fluid substances form crystals when they undergo a process of solidification. Under ideal conditions, the result may be a single crystal, where all of the atoms in the solid fit into the same lattice or crystal structure but, generally, many crystals form simultaneously during solidification, leading to a polycrystalline solid. For example, most metals encountered in everyday life are polycrystals. Crystals are often symmetrically intergrown to form crystal twins. Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. The process of forming a crystalline structure is often referred to as crystallization. pressure While the process of cooling usually results in the generation of a crystalline material, under certain conditions the fluid may be frozen in a noncrystalline state. In most cases, this involves cooling the fluid so rapidly that atoms cannot travel to their lattice sites before they lose mobility. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. It is also often referred to as an amorphous solid, although there are distinct differences between solids and glasses: most notably, the process of forming a glass does not release the latent heat of fusion. For this reason, many scientists consider glassy materials to be viscous liquids rather than solids, although this is a controversial topic; see the entry on glass for more details. glass Crystalline structures occur in all classes of materials, with all types of chemical bonds. Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bonded crystals can form upon solidification of salts, either from a molten fluid or when it condenses from a solution. Covalently bonded crystals are also very common, notable examples being diamond, silica, and graphite. Polymer materials generally will form crystalline regions, but the lengths of the molecules usually prevents complete crystallization. Weak Van der Waals forces can also play a role in a crystal structure; for example, this type of bonding loosely holds together the hexagonal-patterned sheets in graphite. Most crystalline materials have a variety of crystallographic defects. The types and structures of these defects can have a profound effect on the properties of the materials. crystallographic defect crystallographic defect.]] While the term "crystal" has a precise meaning within materials science and solid-state physics, colloquially "crystal" refers to solid objects that exhibit well-defined and often pleasing geometric shapes. Various shapes of such crystals are found in nature. The shape of these crystals is dependent on the types of molecular bonds between the atoms to determine the structure, as well as on the conditions under which they formed. Snowflakes, diamonds, and common salt are common examples of crystals. Some crystalline materials may exhibit special electrical properties such as the ferroelectric effect or the piezoelectric effect. The behaviour of light in crystals is described by crystal optics. In periodic dielectric structures a range of unique optical properties can be expected as described in photonic crystals. Crystallography is the scientific study of crystals and crystal formation.

External links

- [http://www.rockhounds.com/rockshop/xtal/index.html Introduction to Crystallography and Mineral Crystal Systems]
- [http://www.iucr.ac.uk/iucr-top/comm/cteach/pamphlets.html Crystallographic Teaching Pamphlets]
- [http://cst-www.nrl.navy.mil/lattice/spcgrp/ Crystal Lattice Structures] ja:結晶

Fractional crystallization

In chemistry, Fractional Crystallization is a method of refining substances based on differences in solubility. If two or more substances are dissolved in a solvent, they will crystallize out of solution (precipitate) at different rates. Crystallization can be induced by changes in concentration, temperature or other means. Fractional crystallization can be used for purification or analysis. Example: If sugar is dissolved in water and the solution partially frozen, the liquid portion will taste sweeter than the frozen portion because the sugar will be more soluble in the liquid. A more interesting case occurs in geochemistry where elements can become separated during the slow cooling of magma as some remain dissolved while other elements separate out.

Silicon

Silicon (Latin: silicium) is the chemical element in the periodic table that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. It is the second most abundant element in the Earth's crust, making up 25.7% of it by weight. It occurs in clay, feldspar, granite, quartz and sand, mainly in the form of silicon dioxide (also known as silica) and silicates (compounds containing silicon, oxygen and metals). Silicon is the principal component of glass, cement, ceramics, most semiconductor devices, and silicones, the latter a plastic substance often confused with silicon. Silicon is widely used in semiconductors because the semiconductor Germanium has a problem with reverse leakage current flow, and because its native oxide forms better semiconductor/dielectric interfaces than almost all other material combinations.

Notable characteristics

In its crystalline form, silicon has a dark gray color and a metallic luster. Even though it is a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids (except for a combination of nitric acid and hydrofluoric acid) do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared light. Pure silicon crystals are rarely found in nature, as natural silicon is usually found as silica (SiO₂). Pure silicon crystals can be found as inclusions in gold, or in volcanic exhalations. Pure silicon has a negative temperature co-efficient of resistance, since the number of free charge carriers increases with temperature.

Applications

Silicon is a very useful element that is vital to many human industries. Silicon dioxide in the form of sand and clay is an important ingredient of concrete and brick and is also used to produce Portland cement. Silicon is a very important element for plant and animal life. Diatoms extract silica from water to build their protective cell walls. Other uses:
- Pottery/Enamel - It is a refractory material used in high-temperature material production and its silicates are used in making enamels and pottery.
- Steel - Silicon is an important constituent of some steels.
- Glass - Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and with a many different physical properties. Silica is used as a base material to make window glass, containers, and insulators, and many other useful objects.
- Abrasives - Silicon carbide is one of the most important abrasives.
- Semiconductor - Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers. Such control is necessary for transistors, solar cells, semiconductor detectors and other semiconductor devices which are used in electronics and other high-tech applications.
- Photonics - Silicon can be used as a continuous wave raman laser to produce coherent light with a wavelength of 1,698 nm.
- Medical materials - Silicones are flexible compounds containing silicon-oxygen and silicon-carbon bonds; they are widely used in applications such as artificial breast implants and contact lenses.
- LCDs and solar cells - Hydrogenated amorphous silicon has shown promise in the production of low-cost, large-area electronics in applications such as LCDs. It has also shown promise for large-area, low-cost solar cells.
- Construction - Silica is a major ingredient in bricks because of its low chemical activity.

History

Silicon (Latin silex, silicis meaning flint) was first identified by Antoine Lavoisier in 1787, and was later mistaken by Humphry Davy, in 1800, for a compound. In 1811 Gay Lussac and Thénard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. In 1824 Berzelius prepared amorphous silicon using approximately the same method of Lussac. Berzelius also purified the product by repeatedly washing it. Because silicon is an important element in semiconductor and high-tech devices, the high-tech region of Silicon Valley, California, is named after this element.

Occurrence

Silicon is a principal component of aerolites which are a class of meteoroids and also of tektites which is a natural form of glass. Measured by weight, silicon makes up 25.7% of the earth's crust and after oxygen is also the second most abundant element. Elemental silicon is not found in nature. It occurs most often as oxides and as silicates. Sand, amethyst, agate, quartz, rock crystal, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.

Production

Silicon is commercially prepared by the heating of high-purity silica in an electric arc furnace using carbon electrodes. At temperatures over 1900 °C, the carbon reduces the silica to silicon according to the chemical equation :SiO₂ + C → Si + CO₂ Liquid silicon collects in the bottom of the furnace, and is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 99% pure. Using this method, silicon carbide, SiC, can form. However, provided the amount of SiO₂ is kept high, silicon carbide may be eliminated, as explained by this equation: :2SiC + SiO₂ → 3Si + 2CO In 2000, metallurgical grade silicon cost about $ 0.56 per pound ($1.23/kg).[http://minerals.usgs.gov/minerals/pubs/commodity/silicon/760301.pdf]. $

Purification

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Historically, a number of methods have been used to produce high-purity silicon.

Physical methods

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product. In zone melting, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and resolidifies behind it. Since most impurities tend to remain in the molten region rather than resolidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity was desired.

Chemical methods

Today, silicon is instead purified by converting it to a silicon compound that can be more easily purified than silicon itself, and then converting that silicon compound back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity silicon. In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them according to chemical reactions like :2 HSiCl₃ → Si + 2 HCl + SiCl₄ Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of 1 part per billion or less. At one time, DuPont produced ultrapure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon according to the chemical equation :SiCl₄ + 2 Zn → Si + 2 ZnCl₂ However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process.

Crystallization

The majority of silicon crystals grown for device production are produced by the Czochralski process, since it is the cheapest method available. However, silicon single-crystals grown by the Czochralski method contain impurities since the crucible which contains the melt dissolves. For certain electronic devices, particularly those required for high power applications, silicon grown by the Czochralski method is not pure enough. For these applications, float-zone silicon (FZ-Si) can be used instead.

Isotopes

Silicon has nine isotopes, with mass numbers from 25-33. Si-28 (the most abundant isotope, at 92.23%), Si-29 (4.67%), and Si-30 (3.1%) are stable; Si-32 is a radioactive isotope produced by argon decay. Its half-life, has been determined to be approximately 132 years, and it decays by beta emission to P-32 (which has a 14.28 day half-life [http://www.sciencegateway.org/isotope/phosp32.html]) and then to S-32.

Precautions

A serious lung disease known as silicosis often occurred in miners, stonecutters, and others who were engaged in work where siliceous dust was inhaled in great quantities.

Silicon is not silicone

Casual speakers often make the mistake of interchanging the words silicon and silicone; they are not the same. The first, of course, is the element. The second is a class of chemical compounds (in particular, inorganic polymers) that contain the element silicon, the most notable members of the class being silicone rubbers and silicone gels.

Silicon-based life

Since Silicon is analogous to Carbon, some scientists have proposed the possibility of Silicon-based life. This concept is especially popular in science-fiction.

Compounds

For Silicates see category Silicate. See also Silane (SiH₄), silicic acid (H₄SiO₄), Silicon carbide (SiC), Silicon dioxide (SiO₂), Silicon tetrachloride (SiCl₄), Silicon tetrafluoride (SiF₄), Trichlorosilane (HSiCl₃)

References

- [http://periodic.lanl.gov/elements/14.html Los Alamos National Laboratory – Silicon]

External links

- [http://www.webelements.com/webelements/elements/text/Si/key.html WebElements.com – Silicon]
- [http://mineral.galleries.com/minerals/elements/silicon/silicon.htm Mineral.Galleries.com – Silicon]
- [http://www.processpecialties.com/siliconp.htm Silicon wafer processing information by Process Specialties Inc] Category:Metalloids Category:Semiconductor materials ko:규소 ja:ケイ素 th:ซิลิคอน

Oxygen

Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually covalently bonded with other elements. Unbound oxygen (usually called molecular oxygen, O₂, a diatomic molecule) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago) and as a product of the metabolic action of early anaerobes (archaea and bacteria). The presence of free oxygen drove most of the organisms then living to extinction. The atmospheric abundance of free oxygen in later geological epochs and up to the present has been largely driven by photosynthetic organisms, roughly three quarters by phytoplankton and algae in the oceans and one quarter from terrestrial plants.

Characteristics

At standard temperature and pressure, oxygen is mostly found as a gas consisting of a diatomic molecule with the chemical formula O₂. O₂ has two energetic forms:
- The low-energy predominant single-bonded diradical triplet oxygen. This native diradical quality of oxygen contributes to its destructive chemical nature. This form is stabilized by the degeneracy effect.
- The high-energy double-bonded molecule singlet oxygen. Oxygen is a major component of air, produced by plants during photosynthesis, and is necessary for aerobic respiration in animals. The word oxygen derives from two words in Greek, οξυς (oxys) (acid, sharp) and γεινομαι (geinomai) (engender). The name "oxygen" was chosen because, at the time it was discovered in the late 18th century, it was believed that all acids contained oxygen. The definition of acid has since been revised to not require oxygen in the molecular structure. Liquid O₂ and solid O₂ have a light blue color and both are highly paramagnetic. Liquid O₂ is usually obtained by the fractional distillation of liquid air. Liquid and solid O₃ (ozone) have a deeper color of blue. A recently discovered allotrope of oxygen, tetraoxygen (O₄), is a deep red solid that is created by pressurizing O₂ to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O₂ or O₃.

Applications

Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine (as oxygen therapy). People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding (such as the oxyacetylene torch), and in the making of steel and methanol. Oxygen presents two absorption bands centered in the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform. This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as possibility to monitor the carbon cycle from satellite, thus in a global scale. Oxygen, as a mild euphoric, has a history of recreational use that extends into modern times. Oxygen bars can be seen at parties to this day. In the 19th century, oxygen was often mixed with nitrous oxide to promote an analgesic effect; indeed, such a mixture (Entonox) is commonly used in medicine today.

History

Oxygen was first discovered by Michał Sędziwój, Polish alchemist and philosopher in late 16th century. Sędziwój assumed the existence of oxygen by warming nitre (saltpeter). He thought of the gas given off as "the elixir of life". Oxygen was again discovered by the Swedish pharmacist Carl Wilhelm Scheele sometime before 1773, but the discovery was not published until after the independent discovery by Joseph Priestley on August 1, 1774, who called the gas dephlogisticated air (see phlogiston theory). Priestley published his discoveries in 1775 and Scheele in 1777; consequently Priestley is usually given the credit. It was named by Antoine Laurent Lavoisier after Priestley's publication in 1775.

Occurrence

Oxygen is the second most common component of the earth's atmosphere (20.947% by volume).

Compounds

Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (which is the origin of the original definition of oxidation). The only elements to escape the possibility of oxidation are a few of the noble gases. The most famous of these oxides is dihydrogen monoxide, or water (H₂O). Other well known examples include compounds of carbon and oxygen, such as carbon dioxide (CO₂), alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO₃⁻), perchlorates (ClO₄⁻), chromates (CrO₄²⁻), dichromates (Cr₂O₇²⁻), permanganates (MnO₄⁻), and nitrates (NO₃⁻) are strong oxidizing agents in and of themselves. Many metals such as iron bond with oxygen atoms, iron (III) oxide (Fe₂O₃). Ozone (O₃) is formed by electrostatic discharge in the presence of molecular oxygen. A double oxygen molecule (O₂)₂ is known and is found as a minor component of liquid oxygen. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.

Isotopes

Oxygen has fifteen known isotopes with atomic masses ranging from 12 to 26. Three of them are stable and twelve are radioactive. The radioisotopes all have half lives of less than three minutes. The stable isotopes have mass numbers of 16, 17 and 18, of which oxygen-16 is the most common (over 99%).

Precautions

Oxygen can be toxic at elevated partial pressures (i.e. high relative concentrations). This is important in some forms of scuba diving, such as with a rebreather. Certain derivatives of oxygen, such as ozone (O₃), singlet oxygen, hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns. The fire that killed the Apollo 1 crew on a test launchpad spread so rapidly because the pure oxygen atmosphere was at normal atmospheric pressure instead of the one third pressure that would be used during an actual launch. (See partial pressure.) Oxygen derivatives are prone to form free radicals, especially in metabolic processes. Because they can cause severe damage to cells and their DNA, they are thought to be related to cancer and aging.

References

- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://physics.nist.gov/cgi-bin/AtData/main_asd Nist atomic spectra database]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes Fourteenth Edition]: Chart of the Nuclides, General Electric Company, 1989

External links

- [http://www.priestleysociety.net Priestley Society, Dedicated to Joseph Priestley the man who discovered oxygen]
- [http://www.best-home-remedies.com/minerals/oxygen.htm Oxygen - Benefits, Deficiency Symptoms And Food Sources]
- [http://www.josephpriestley.info Joseph Priestley Information Website, about the man who discovered oxygen]
- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://www.webelements.com/webelements/elements/text/O/index.html WebElements.com – Oxygen]
- [http://education.jlab.org/itselemental/ele008.html It's Elemental – Oxygen]
- [http://members.tripod.com/tjaartdb0/html/oxygen_toxicity.html Oxygen Toxicity]
- [http://www.uigi.com/oxygen.html Oxygen (O2) Properties, Uses, Applications]
- [http://www.compchemwiki.org/index.php?title=Oxygen Computational Chemistry Wiki]
- [http://koti.mbnet.fi/antitz/dime/en Tests with liquid oxygen :-)] Category:Nonmetals Category:Chalcogens als:Sauerstoff