1.
Rhyolite
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Rhyolite is an igneous, volcanic rock, of felsic composition. It may have any texture from glassy to aphanitic to porphyritic, the mineral assemblage is usually quartz, sanidine and plagioclase. Biotite and hornblende are common accessory minerals and it is the extrusive equivalent to granite. Rhyolite can be considered as the equivalent to the plutonic granite rock. Due to their content of silica and low iron and magnesium contents, rhyolite melts are highly polymerized. They also occur as breccias or in volcanic plugs and dikes, rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian. Slower cooling forms microscopic crystals in the lava and results in such as flow foliations, spherulitic, nodular. Some rhyolite is highly vesicular pumice, many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites. Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas, etsch Valley Vulcanite Group near Bolzano and the surrounding area Gréixer rhyolitic complex at Moixeró range Vosges Iceland, all active and extinct central volcanoes, e. g. g. Wichita Mountains within the Southern Oklahoma Aulacogen St, in North American pre-historic times, rhyolite was quarried extensively in eastern Pennsylvania in the United States. Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County, comendite List of rock types Pantellerite Thunderegg University of North Dakota description of rhyolite Information from rocks-rock. com
2.
Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
3.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
4.
Crystal
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A crystal or crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, the scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification, the word crystal derives from the Ancient Greek word κρύσταλλος, meaning both ice and rock crystal, from κρύος, icy cold, frost. Examples of large crystals include snowflakes, diamonds, and table salt, most inorganic solids are not crystals but polycrystals, i. e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, a third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics, Crystals are often used in pseudoscientific practices such as crystal therapy, and, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements. The scientific definition of a crystal is based on the arrangement of atoms inside it. A crystal is a solid where the form a periodic arrangement. For example, when liquid water starts freezing, the change begins with small ice crystals that grow until they fuse. Most macroscopic inorganic solids are polycrystalline, including almost all metals, ceramics, ice, rocks, solids that are neither crystalline nor polycrystalline, such as glass, are called amorphous solids, also called glassy, vitreous, or noncrystalline. These have no periodic order, even microscopically, there are distinct differences between crystalline solids and amorphous solids, most notably, the process of forming a glass does not release the latent heat of fusion, but forming a crystal does. A crystal structure is characterized by its cell, a small imaginary box containing one or more atoms in a specific spatial arrangement. The unit cells are stacked in three-dimensional space to form the crystal, the symmetry of a crystal is constrained by the requirement that the unit cells stack perfectly with no gaps. There are 219 possible crystal symmetries, called space groups. These are grouped into 7 crystal systems, such as cubic crystal system or hexagonal crystal system, Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. Euhedral crystals are those with obvious, well-formed flat faces, anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid. The flat faces of a crystal are oriented in a specific way relative to the underlying atomic arrangement of the crystal. This occurs because some surface orientations are more stable than others, as a crystal grows, new atoms attach easily to the rougher and less stable parts of the surface, but less easily to the flat, stable surfaces
5.
Feldspar
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Feldspars are a group of rock-forming tectosilicate minerals that make up about 40% of the Earths continental crust. Feldspars crystallize from magma as veins in both intrusive and extrusive rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of plagioclase feldspar is known as anorthosite. Feldspars are also found in types of sedimentary rocks. The name feldspar derives from the German Feldspat, a compound of the words Feld, field, and Spat, the change from Spat to -spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar, the alternate spelling, felspar, has largely fallen out of use. This group of minerals consists of tectosilicates, solid solutions between albite and anorthite are called plagioclase, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar, the alkali feldspars are as follows, orthoclase —KAlSi3O8 sanidine —AlSi3O8 microcline —KAlSi3O8 anorthoclase —AlSi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye, microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are also considered alkali feldspars, barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. The barium feldspars are monoclinic and include the following, celsian—BaAl2Si2O8 hyalophane—4O8 The plagioclase feldspars are triclinic, the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae, chemical weathering of feldspars results in the formation of clay minerals. About 20 million tonnes of feldspar were produced in 2010, mostly by three countries, Italy, Turkey, and China, Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, in ceramics, the alkalis in feldspar act as a flux, lowering the melting temperature of a mixture. Fluxes melt at a stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers, ceramics and other uses, such as fillers, accounted for the remainder
6.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
7.
Silicate
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A silicate is a compound containing an anionic silicon compound. The great majority of the silicates are oxides, but hexafluorosilicate, orthosilicate is the anion SiO4−4 or its compounds. Related to orthosilicate are families of anions with the formula 2n−, important members are the cyclic and single chain silicates n and the sheet-forming silicates n. Silicates constitute the majority of Earths crust, as well as the terrestrial planets, rocky moons. Sand, Portland cement, and thousands of minerals are examples of silicates, silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations, hence this class of compounds is very large. Both minerals and synthetic materials fit in this class, in the vast majority of silicates, including silicate minerals, the Si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. In these structures, the bonds to silicon conform to the octet rule. These tetrahedra sometimes occur as isolated SiO4−4 centres, but most commonly, commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. All these such species have negligible solubility in water at normal conditions, silicates are well characterized as solids, but are less commonly observed in solution. The anion SiO4−4 is the base of silicic acid, Si4. Instead, solutions of silicates are usually observed as mixtures of condensed, the nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites. Although the tetrahedron is the coordination geometry for silicon compounds. A well-known example of such a high number is hexafluorosilicate. Octahedral coordination by 6 oxygen centres is observed, at very high pressure, even SiO2 adopts this geometry in the mineral stishovite, a dense polymorph of silica found in the lower mantle of the Earth. This structure is formed by shock during meteorite impacts. In geology and astronomy, the silicate is used to denote types of rock that consist predominantly of silicate minerals. On Earth, a variety of silicate minerals occur in an even wider range of combinations as a result of the processes that form
8.
Aphanite
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Aphanite, or aphanitic as an adjective, is a name given to certain igneous rocks that are so fine-grained that their component mineral crystals are not detectable by the unaided eye. This geological texture results from rapid cooling in volcanic or hypabyssal environments, as a rule, the texture of these rocks is not the same as that of volcanic glass, with volcanic glass being non-crystalline, and having a glass-like appearance. Aphanites are commonly porphyritic, having large crystals embedded in the fine groundmass or matrix, the large inclusions are called phenocrysts. They consist essentially of very fine-grained minerals, such as feldspar, with hornblende or augite, and may contain also biotite, quartz. Andesite Basalt Basanite Dacite Felsite Phonolite Rhyolite Trachyte This article incorporates text from a now in the public domain, Chisholm, Hugh
9.
Matrix (geology)
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The matrix or groundmass of rock is the finer-grained mass of material wherein larger grains, crystals or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic and this porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix, also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock called yellow ground. The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt and it also used to describe the rock material in which a fossil is embedded. All sediments are at first in an incoherent condition, and in this state they may remain for an indefinite period. Millions of years have elapsed since some of the early Tertiary strata gathered on the floor, yet they are quite friable. The pressure of newer sediments on underlying masses is one cause of this change. More efficiency is generally ascribed to the action of percolating water, the redeposited cementing material is most commonly calcareous or siliceous. Limestones, which were originally a loose accumulation of shells, corals, the change of aragonite to calcite and of calcite to dolomite, by forming new crystalline masses in the interior of the rock, usually also accelerates consolidations. Silica is less soluble in ordinary waters, but even this ingredient of rocks is dissolved and redeposited with great frequency. Others contain fine scales of kaolin or of mica, argillaceous materials may be compacted by mere pressure, like graphite and other scaly minerals
10.
Phenocryst
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A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a difference in the size of the crystals are called porphyries. Phenocrysts often have euhedral forms, either due to growth within a magma. Normally the term phenocryst is not used unless the crystals are directly observable, phenocrysts below this level, but still larger than the groundmass crystals, are termed microphenocrysts. Very large phenocrysts are termed megaphenocrysts, some rocks contain both microphenocrysts and megaphenocrysts. In metamorphic rocks, crystals similar to phenocrysts are called porphyroblasts, phenocrysts are more often found in the lighter igneous rocks such as felsites and andesites, although they occur throughout the igneous spectrum including in the ultramafics. The largest crystals found in some pegmatites are often phenocrysts being significantly larger than the other minerals, rocks can be classified according to the nature, size and abundance of phenocrysts, and the presence or absence of phenocrysts is often noted when a rock name is determined. Porphyritic rocks are named using mineral name modifiers, normally in decreasing order of abundance. Thus when olivine forms the primary phenocrysts in a basalt, the name may be refined from basalt to porphyritic olivine basalt or olivine phyric basalt. Similarly, a basalt with olivine as the dominate phenocrysts, but with lesser amounts of plagioclase phenocrysts, categorizing a rock as aphyric or as sparsely phyric is often a question of whether a significant number of crystals exceed the minimum size. Geologists use phenocrysts to help determine rock origins and transformations, as when and whether crystals form depends on pressure, fumiko Shido first applied this technique to oceanic basalts, further development came from Tsugio Shibata, and from W. B. Plagioclase phenocrysts often exhibit zoning with a more calcic core surrounded by progressively more sodic rinds and this zoning reflects the change in magma composition as crystallization progresses. In rapakivi granites, phenocrysts of orthoclase are enveloped within rinds of sodic plagioclase such as oligoclase, in shallow intrusives or volcanic flows phenocrysts which formed before eruption or shallow emplacement are surrounded by a fine-grained to glassy matrix. These volcanic phenocrysts often show flow banding, an arrangement of lath-shaped crystals. These characteristics provide clues to the rocks origins, similarly, intragranular microfractures and any intergrowth among crystals provide additional clues. Williams, Howel, Turner, Francis J. & Gilbert, Charlse M. Petrography, proceedings of the Ocean Drilling Program, Vol.187 Initial Reports
11.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
12.
Purple
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Purple is a color intermediate between blue and red. It is similar to violet, but unlike violet, which is a color with its own wavelength on the visible spectrum of light, purple is a composite color made by combining red. According to surveys In Europe and the U. S. purple is the color most often associated with royalty, magic, mystery, when combined with pink, it is associated with eroticism, femininity and seduction. Purple was the color worn by Roman magistrates, it became the color worn by the rulers of the Byzantine Empire and the Holy Roman Empire. Similarly in Japan, the color is associated with the Emperor. The complementary color of purple is yellow, the first recorded use of the word purple in the English language was in the year 975 AD. In heraldry, the word purpure is used for purple, in the traditional color wheel used by painters, violet and purple are both placed between red and blue. Purple occupies the space closer to red, between crimson and violet, violet is closer to blue, and is usually less saturated than purple. While the two look similar, from the point of view of optics there are important differences. There is no such thing as the wavelength of purple light, monochromatic violet light cannot be produced by the red-green-blue color system, the method used to create colors on a television screen or computer display. This means that when light strikes the eye, the S-cone should be stimulated strongly. The resulting color has the same hue as pure violet, however, one curious psychophysical difference between purple and violet is their appearance with an increase in luminance. Violet, as it brightens, looks more and more blue, the same effect does not happen with purple. This is the result of what is known as the Bezold–Brücke shift, while the scientific definitions of violet and purple are clear, the cultural definitions are more varied. The color known in antiquity as Tyrian purple ranged from crimson to a deep bluish-purple, in France, purple is defined as a dark red, inclined toward violet. The color called purple by the French, pourpre, contains red and half the amount of blue of the color called purple in the United States. In German, this color is sometimes called Purpurrot to avoid confusion, Purple first appeared in prehistoric art during the Neolithic era. These works have been dated to between 16,000 and 25,000 BC, as early as the 15th century BC the citizens of Sidon and Tyre, two cities on the coast of Ancient Phoenicia, were producing purple dye from a sea snail called the spiny dye-murex
13.
Plagioclase
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Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a mineral with a specific chemical composition, plagioclase is a continuous solid solution series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826, the series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the minerals crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or record-groove effect, plagioclase is a major constituent mineral in the Earths crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a constituent of rock in the highlands of the Earths moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars, the extinction angle is an optical characteristic and varies with the albite fraction. There are several named plagioclase feldspars that fall between albite and anorthite in the series, the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its pure white color. It is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes, often with rarer minerals like tourmaline. The intermediate members of the group are very similar to each other. Bytownite, named after the name for Ottawa, Canada, is a rare mineral occasionally found in more basic rocks. Labradorite is the characteristic feldspar of the basic rock types such as diorite, gabbro, andesite. Labradorite frequently shows an iridescent display of colors due to light refracting within the lamellae of the crystal and it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite which is composed almost entirely of plagioclase. A variety of known as spectrolite is found in Finland. Andesine is a mineral of rocks such as diorite which contain a moderate amount of silica. Oligoclase is common in granite, syenite, diorite, and gneiss and it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, sunstone is mainly oligoclase with flakes of hematite
14.
Roman Empire
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Civil wars and executions continued, culminating in the victory of Octavian, Caesars adopted son, over Mark Antony and Cleopatra at the Battle of Actium in 31 BC and the annexation of Egypt. Octavians power was then unassailable and in 27 BC the Roman Senate formally granted him overarching power, the imperial period of Rome lasted approximately 1,500 years compared to the 500 years of the Republican era. The first two centuries of the empires existence were a period of unprecedented political stability and prosperity known as the Pax Romana, following Octavians victory, the size of the empire was dramatically increased. After the assassination of Caligula in 41, the senate briefly considered restoring the republic, under Claudius, the empire invaded Britannia, its first major expansion since Augustus. Vespasian emerged triumphant in 69, establishing the Flavian dynasty, before being succeeded by his son Titus and his short reign was followed by the long reign of his brother Domitian, who was eventually assassinated. The senate then appointed the first of the Five Good Emperors, the empire reached its greatest extent under Trajan, the second in this line. A period of increasing trouble and decline began with the reign of Commodus, Commodus assassination in 192 triggered the Year of the Five Emperors, of which Septimius Severus emerged victorious. The assassination of Alexander Severus in 235 led to the Crisis of the Third Century in which 26 men were declared emperor by the Roman Senate over a time span. It was not until the reign of Diocletian that the empire was fully stabilized with the introduction of the Tetrarchy, which saw four emperors rule the empire at once. This arrangement was unsuccessful, leading to a civil war that was finally ended by Constantine I. Constantine subsequently shifted the capital to Byzantium, which was renamed Constantinople in his honour and it remained the capital of the east until its demise. Constantine also adopted Christianity which later became the state religion of the empire. However, Augustulus was never recognized by his Eastern colleague, and separate rule in the Western part of the empire ceased to exist upon the death of Julius Nepos. The Eastern Roman Empire endured for another millennium, eventually falling to the Ottoman Turks in 1453, the Roman Empire was among the most powerful economic, cultural, political and military forces in the world of its time. It was one of the largest empires in world history, at its height under Trajan, it covered 5 million square kilometres. It held sway over an estimated 70 million people, at that time 21% of the entire population. Throughout the European medieval period, attempts were made to establish successors to the Roman Empire, including the Empire of Romania, a Crusader state. Rome had begun expanding shortly after the founding of the republic in the 6th century BC, then, it was an empire long before it had an emperor
15.
Basalt
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Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually 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 and these phenocrysts usually 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 texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Mars, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
16.
Granite
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Granite is a common type of felsic intrusive igneous rock that is granular and phaneritic in texture. Granites can be white, pink, or gray in color. The word granite comes from the Latin granum, a grain, in reference to the structure of such a holocrystalline rock. By definition, granite is a rock with at least 20% quartz. The term granitic means granite-like and is applied to granite and a group of igneous rocks with similar textures and slight variations in composition. Occasionally some individual crystals are larger than the groundmass, in case the texture is known as porphyritic. A granitic rock with a texture is known as a granite porphyry. Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks, petrographic examination is required for identification of specific types of granitoids. The extrusive igneous rock equivalent of granite is rhyolite, Granite is nearly always massive, hard and tough, and therefore it has gained widespread use throughout human history, and more recently as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3, its compressive strength usually lies above 200 MPa, and its viscosity near STP is 3–6 •1019 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C, it is reduced in the presence of water. Granite has poor primary permeability, but strong secondary permeability, true granite according to modern petrologic convention contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase, the rock is referred to as alkali feldspar granite, when a granitoid contains less than 10% orthoclase, it is called tonalite, pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite, two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites. A worldwide average of the composition of granite, by weight percent, based on 2485 analyses. Much of it was intruded during the Precambrian age, it is the most abundant basement rock that underlies the relatively thin veneer of the continents. Outcrops of granite tend to form tors and rounded massifs, granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite often occurs as small, less than 100 km² stock masses
17.
Magma
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Besides molten rock, magma may also contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or solidify underground to form an intrusion, magma is capable of intruding into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock. Magma is a complex high-temperature fluid substance, temperatures of most magmas are in the range 700 °C to 1300 °C, but very rare carbonatite magmas may be as cool as 600 °C, and komatiite magmas may have been as hot as 1600 °C. Environments of magma formation and compositions are commonly correlated, environments include subduction zones, continental rift zones, mid-ocean ridges and hotspots. Despite being found in such locales, the bulk of the Earths crust. Except for the outer core, most of the Earth takes the form of a rheid. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earths surface, magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. By definition rock formed of solidified magma is called igneous rock, melting of solid rocks to form magma is controlled by three physical parameters, temperature, pressure, and composition. Mechanisms are discussed in the entry for igneous rock, as a rock melts, its volume changes. When enough rock is melted, the small globules of melt link up, under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source. The degree of melting is critical for determining what type of magma is produced. The degree of partial melting required to form a melt can be estimated by considering the relative enrichment of incompatible elements versus compatible elements, incompatible elements commonly include potassium, barium, cesium, and rubidium. Rock types produced by small degrees of melting in the Earths mantle are typically alkaline. Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts, pegmatite may be produced by low degrees of partial melting of the crust. Some granite-composition magmas are eutectic melts, and they may be produced by low to high degrees of melting of the crust. At high degrees of melting of the crust, granitoids such as tonalite, granodiorite and monzonite can be produced. Being only the time in recorded history that magma had been reached, IDDP decided to invest in the hole. A cemented steel case was constructed in the hole with a perforation at the close to the magma
18.
Volcano
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A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. This type of volcanism falls under the umbrella of plate hypothesis volcanism, Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called hotspots, for example Hawaii, are postulated to arise from upwelling diapirs with magma from the boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology, at the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Most divergent plate boundaries are at the bottom of the oceans, therefore, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire. Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
19.
Porphyry copper
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Porphyry copper deposits are copper orebodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name, in later stages, circulating meteoric fluids may interact with the magmatic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals in often stockwork-forming hairline fractures and veins. Because of their volume, porphyry orebodies can be economic from copper concentrations as low as 0. 15% copper and can have economic amounts of by-products such as molybdenum, silver. In some mines, those metals are the main product, some mines exploit porphyry deposits that contain sufficient gold or molybdenum, but little or no copper. Porphyry copper deposits are currently the largest source of copper ore, only a few are identified in Africa, in Namibia and Zambia, none are known in Antarctica. The greatest concentration of the largest copper porphyrys is in northern Chile, almost all mines exploiting large porphyry deposits produce from open pits. Porphyry copper deposits represent an important resource and the dominant source of copper that is mined today to satisfy global demand, throughout the Phanerozoic an estimated 125,895 porphyry copper deposits were formed, however, 62% of them have been removed by uplift and erosion. Thus, 38% remain in the crust, of which there are 574 known deposits that are at the surface and it is estimated that the Earth’s porphyry copper deposits contain approximately 1. 7×1011 tonnes of copper. Porphyry deposits represent an important resource of copper, however, they are important sources of gold. In general, porphyry deposits are characterized by low grades of ore mineralization, Porphyry deposits are formed in arc-related settings and are associated with subduction zone magmas. Porphyry deposits tend to occur in linear, orogen-parallel belts, there also appears to be discrete time periods in which porphyry deposit formation appears to be concentrated or preferred. For copper-molybdenum porphyry deposits, formation is broadly concentrated in three periods, Palaeocene-Eocene, Eocene-Oligocene, and middle Miocene-Pliocene. For both porphyry and epithermal gold deposits, they are generally from the period ranging from the middle Miocene to the Recent period. Most large-scale porphyry deposits have an age of less than 20 million years, however there are notable exceptions, such as the 438 million year old Cadia-Ridgeway deposit in New South Wales. Numerous world-class porphyry copper-gold deposits are hosted by high-K or shoshonitic intrusions, the magmas responsible for porphyry formation are conventionally thought to be generated by the partial melting of the upper part of post-subduction, stalled slabs that are altered by seawater. Shallow subduction of young, buoyant slabs can result in the production of adakitic lavas via partial melting, mantle melting can also be induced by transitions from convergent to transform margins, as well as the steepening and trenchward retreat of the subducted slab. However, the latest belief is that dehydration that occurs at the blueschist-eclogite transition affects most subducted slabs, after dehydration, solute-rich fluids are released from the slab and metasomatise the overlying mantle wedge of MORB-like asthenosphere, enriching it with volatiles and large ion lithophile elements
20.
Gold
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Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
21.
Copper
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Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with high thermal and electrical conductivity. A freshly exposed surface of copper has a reddish-orange color. Copper is one of the few metals that occur in nature in directly usable metallic form as opposed to needing extraction from an ore and this led to very early human use, from c.8000 BC. Copper used in buildings, usually for roofing, oxidizes to form a green verdigris, Copper is sometimes used in decorative art, both in its elemental metal form and in compounds as pigments. Copper compounds are used as agents, fungicides, and wood preservatives. Copper is essential to all living organisms as a trace dietary mineral because it is a key constituent of the enzyme complex cytochrome c oxidase. In molluscs and crustaceans, copper is a constituent of the blood pigment hemocyanin, replaced by the hemoglobin in fish. In humans, copper is found mainly in the liver, muscle, the adult body contains between 1.4 and 2.1 mg of copper per kilogram of body weight. The filled d-shells in these elements contribute little to interatomic interactions, unlike metals with incomplete d-shells, metallic bonds in copper are lacking a covalent character and are relatively weak. This observation explains the low hardness and high ductility of single crystals of copper, at the macroscopic scale, introduction of extended defects to the crystal lattice, such as grain boundaries, hinders flow of the material under applied stress, thereby increasing its hardness. For this reason, copper is supplied in a fine-grained polycrystalline form. The softness of copper partly explains its high conductivity and high thermal conductivity. The maximum permissible current density of copper in open air is approximately 3. 1×106 A/m2 of cross-sectional area, Copper is one of a few metallic elements with a natural color other than gray or silver. Pure copper is orange-red and acquires a reddish tarnish when exposed to air, as with other metals, if copper is put in contact with another metal, galvanic corrosion will occur. A green layer of verdigris can often be seen on old structures, such as the roofing of many older buildings. Copper tarnishes when exposed to sulfur compounds, with which it reacts to form various copper sulfides. There are 29 isotopes of copper, 63Cu and 65Cu are stable, with 63Cu comprising approximately 69% of naturally occurring copper, both have a spin of 3⁄2
22.
Molybdenum
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Molybdenum is a chemical element with symbol Mo and atomic number 42. The name is from Neo-Latin molybdaenum, from Ancient Greek Μόλυβδος molybdos, meaning lead, molybdenum minerals have been known throughout history, but the element was discovered in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm, molybdenum does not occur naturally as a free metal on Earth, it is found only in various oxidation states in minerals. The free element, a metal with a gray cast, has the sixth-highest melting point of any element. It readily forms hard, stable carbides in alloys, and for this reason most of production of the element is used in steel alloys. Most molybdenum compounds have low solubility in water, but when molybdenum-bearing minerals contact oxygen and water, industrially, molybdenum compounds are used in high-pressure and high-temperature applications as pigments and catalysts. Molybdenum-bearing enzymes are by far the most common catalysts for breaking the chemical bond in atmospheric molecular nitrogen in the process of biological nitrogen fixation. At least 50 molybdenum enzymes are now known in bacteria and animals and these nitrogenases contain molybdenum in a form different from other molybdenum enzymes, which all contain fully oxidized molybdenum in a molybdenum cofactor. These various molybdenum cofactor enzymes are vital to the organisms, and molybdenum is an element for life in all higher eukaryote organisms. In its pure form, molybdenum is a metal with a Mohs hardness of 5.5. It has a point of 2,623 °C, of the naturally occurring elements, only tantalum, osmium, rhenium, tungsten. Weak oxidation of molybdenum starts at 300 °C and it has one of the lowest coefficients of thermal expansion among commercially used metals. The tensile strength of molybdenum wires increases about 3 times, from about 10 to 30 GPa, there are 35 known isotopes of molybdenum, ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with masses of 92,94,95,96,97,98. Of these naturally occurring isotopes, only molybdenum-100 is unstable, molybdenum-98 is the most abundant isotope, comprising 24. 14% of all molybdenum. Molybdenum-100 has a half-life of about 1019 y and undergoes double beta decay into ruthenium-100, molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns. All unstable isotopes of molybdenum decay into isotopes of niobium, technetium, as also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m, in 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of molybdenum-99
23.
Lead
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Lead is a chemical element with atomic number 82 and symbol Pb. When freshly cut, it is bluish-white, it tarnishes to a dull gray upon exposure to air and it is a soft, malleable, and heavy metal with a density exceeding that of most common materials. Lead has the second-highest atomic number of the stable elements. Lead is a relatively unreactive post-transition metal and its weak metallic character is illustrated by its amphoteric nature and tendency to form covalent bonds. Compounds of lead are found in the +2 oxidation state. Exceptions are mostly limited to organolead compounds, like the lighter members of the group, lead exhibits a tendency to bond to itself, it can form chains, rings, and polyhedral structures. Lead is easily extracted from its ores and was known to people in Western Asia. A principal ore of lead, galena, often bears silver, Lead production declined after the fall of Rome and did not reach comparable levels again until the Industrial Revolution. Nowadays, global production of lead is about ten million tonnes annually, Lead has several properties that make it useful, high density, low melting point, ductility, and relative inertness to oxidation. In the late 19th century, lead was recognized as poisonous, Lead is a neurotoxin that accumulates in soft tissues and bones, damaging the nervous system and causing brain disorders and, in mammals, blood disorders. A lead atom has 82 electrons, arranged in a configuration of 4f145d106s26p2. The combined first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, leads upper neighbor in group 14. This is unusual since ionization energies generally fall going down a group as an elements outer electrons become more distant from the nucleus, the similarity is caused by the lanthanide contraction—the decrease in element radii from lanthanum to lutetium, and the relatively small radii of the elements after hafnium. The contraction is due to shielding of the nucleus by the lanthanide 4f electrons. The combined first four ionization energies of lead exceed those of tin, for this reason lead, unlike tin, mostly forms compounds in which it has an oxidation state of +2, rather than +4. Relativistic effects, which become particularly prominent at the bottom of the periodic table, as a result, the 6s electrons of lead become reluctant to participate in bonding, a phenomenon called the inert pair effect. A related outcome is that the distance between nearest atoms in crystalline lead is unusually long, the lighter group 14 elements form stable or metastable allotropes having the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp3 orbitals
24.
Tin
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Tin is a chemical element with symbol Sn and atomic number 50. It is a metal in group 14 of the periodic table. It is obtained chiefly from the mineral cassiterite, which contains tin dioxide, Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, metallic tin is not easily oxidized in air. The first alloy used on a scale was bronze, made of tin and copper. After 600 BC, pure metallic tin was produced, pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony, and lead, was used for flatware from the Bronze Age until the 20th century. In modern times, tin is used in alloys, most notably tin/lead soft solders. Another large application for tin is corrosion-resistant tin plating of steel, inorganic tin compounds are rather non-toxic. Because of its low toxicity, tin-plated metal was used for packaging as tin cans. However, overexposure to tin may cause problems with metabolizing essential trace elements such as copper and zinc, Tin is a soft, malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a sound known as the tin cry can be heard from the twinning of the crystals. Tin melts at the low temperature of about 232 °C, the lowest in group 14, the melting point is further lowered to 177.3 °C for 11 nm particles. β-tin, which is stable at and above room temperature, is malleable, in contrast, α-tin, which is stable below 13.2 °C, is brittle. α-tin has a cubic crystal structure, similar to diamond. α-tin has no properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications and these two allotropes, α-tin and β-tin, are more commonly known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C, in cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as tin pest. Commercial grades of tin resist transformation because of the effect of the small amounts of bismuth, antimony, lead
25.
Zinc
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Zinc is a chemical element with the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table, in some respects zinc is chemically similar to magnesium, both elements exhibit only one normal oxidation state, and the Zn2+ and Mg2+ ions are of similar size. Zinc is the 24th most abundant element in Earths crust and has five stable isotopes, the most common zinc ore is sphalerite, a zinc sulfide mineral. The largest workable lodes are in Australia, Asia, and the United States, Zinc is refined by froth flotation of the ore, roasting, and final extraction using electricity. Zinc metal was not produced on a large scale until the 12th century in India and was unknown to Europe until the end of the 16th century, the mines of Rajasthan have given definite evidence of zinc production going back to the 6th century BC. To date, the oldest evidence of pure zinc comes from Zawar, in Rajasthan, alchemists burned zinc in air to form what they called philosophers wool or white snow. The element was named by the alchemist Paracelsus after the German word Zinke. German chemist Andreas Sigismund Marggraf is credited with discovering pure metallic zinc in 1746, work by Luigi Galvani and Alessandro Volta uncovered the electrochemical properties of zinc by 1800. Corrosion-resistant zinc plating of iron is the application for zinc. Other applications are in batteries, small non-structural castings. A variety of compounds are commonly used, such as zinc carbonate and zinc gluconate, zinc chloride, zinc pyrithione, zinc sulfide. Zinc is an essential mineral perceived by the public today as being of exceptional biologic and public health importance, Zinc deficiency affects about two billion people in the developing world and is associated with many diseases. In children, deficiency causes growth retardation, delayed sexual maturation, infection susceptibility, enzymes with a zinc atom in the reactive center are widespread in biochemistry, such as alcohol dehydrogenase in humans. Consumption of excess zinc can cause ataxia, lethargy and copper deficiency, Zinc is a bluish-white, lustrous, diamagnetic metal, though most common commercial grades of the metal have a dull finish.6 pm. The metal is hard and brittle at most temperatures but becomes malleable between 100 and 150 °C, above 210 °C, the metal becomes brittle again and can be pulverized by beating. Zinc is a conductor of electricity. For a metal, zinc has relatively low melting and boiling points, the melting point is the lowest of all the transition metals aside from mercury and cadmium. Many alloys contain zinc, including brass, Other metals long known to form binary alloys with zinc are aluminium, antimony, bismuth, gold, iron, lead, mercury, silver, tin, magnesium, cobalt, nickel, tellurium, and sodium
26.
Rhenium
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Rhenium is a chemical element with symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table, with an estimated average concentration of 1 part per billion, rhenium is one of the rarest elements in the Earths crust. Rhenium shows in its compounds a variety of oxidation states ranging from −1 to +7. Discovered in 1925, rhenium was the last stable element to be discovered and it was named after the river Rhine in Europe. Nickel-based superalloys of rhenium are used in the chambers, turbine blades. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element, rhenium was the last-discovered of the elements that have a stable isotope. The existence of an element at this position in the periodic table had been first predicted by Dmitri Mendeleev. Other calculated information was obtained by Henry Moseley in 1914 and it is generally considered to have been discovered by Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925 they reported that they had detected the element in platinum ore and they also found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite and it was estimated in 1968 that 75% of the rhenium metal in the United States was used for research and the development of refractory metal alloys. It took several years from that point before the superalloys became widely used, in 1908, Japanese chemist Masataka Ogawa announced that he had discovered the 43rd element and named it nipponium after Japan. However, recent analysis indicated the presence of rhenium, not element 43, the symbol Np was later used for the element neptunium, and the name nihonium, also named after Japan, along with symbol Nh, represents element 113. Rhenium is a metal with one of the highest melting points of all elements, exceeded by only tungsten. It also has one of the highest boiling point of all elements and it is also one of the densest, exceeded only by platinum, iridium and osmium. Rhenium has a hexagonal close-packed crystal structure, with parameters a =276.1 pm. Its usual commercial form is a powder, but this element can be consolidated by pressing and sintering in a vacuum or hydrogen atmosphere and this procedure yields a compact solid having a density above 90% of the density of the metal. When annealed this metal is very ductile and can be bent, coiled, rhenium-molybdenum alloys are superconductive at 10 K, tungsten-rhenium alloys are also superconductive around 4–8 K, depending on the alloy. Rhenium metal superconducts at 1.697 ±0.006 K, in bulk form and at room temperature and atmospheric pressure, the element resists alkalis, sulfuric acid, hydrochloric acid, dilute nitric acid, and aqua regia
27.
Tungsten
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Tungsten, also known as wolfram, is a chemical element with symbol W and atomic number 74. The word tungsten comes from the Swedish language tung sten, which translates to heavy stone. Its name in Swedish is volfram, however, in order to distinguish it from scheelite, a hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth almost exclusively in chemical compounds. It was identified as a new element in 1781, and first isolated as a metal in 1783 and its important ores include wolframite and scheelite. The free element is remarkable for its robustness, especially the fact that it has the highest melting point of all the elements discovered, melting at 3,422 °C,6,192 °F. Its high density is 19.3 times that of water, comparable to that of uranium and gold, polycrystalline tungsten is an intrinsically brittle and hard material, making it difficult to work. However, pure single-crystalline tungsten is more ductile, and can be cut with a hard-steel hacksaw, tungstens many alloys have numerous applications, including incandescent light bulb filaments, X-ray tubes, electrodes in TIG welding, superalloys, and radiation shielding. Tungstens hardness and high density give it military applications in penetrating projectiles, tungsten compounds are also often used as industrial catalysts. Tungsten is the metal from the third transition series that is known to occur in biomolecules. It is the heaviest element known to be essential to any living organism, tungsten interferes with molybdenum and copper metabolism and is somewhat toxic to animal life. In its raw form, tungsten is a hard metal that is often brittle. If made very pure, tungsten retains its hardness, and becomes malleable enough that it can be worked easily and it is worked by forging, drawing, or extruding. Tungsten objects are commonly formed by sintering. Of all metals in pure form, tungsten has the highest melting point, lowest vapor pressure, although carbon remains solid at higher temperatures than tungsten, carbon sublimes, rather than melts, so tungsten is considered to have a higher melting point. Tungsten has the lowest coefficient of expansion of any pure metal. The low thermal expansion and high melting point and tensile strength of tungsten originate from strong covalent bonds formed between tungsten atoms by the 5d electrons, alloying small quantities of tungsten with steel greatly increases its toughness. Tungsten exists in two crystalline forms, α and β. The former has a cubic structure and is the more stable form
28.
Carbonate rock
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Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite. Calcite can be dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH. Calcite exhibits a characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures, karst topography and caves develop in carbonate rocks because of their solubility in dilute acidic groundwater. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation, marble is the metamorphic carbonate rock. Rare igneous carbonate rocks exist as intrusive carbonatites and even rarer volcanic carbonate lava
29.
Skarn
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Skarns or tactites are calcium-bearing calc–silicate rocks. Skarns are most often formed at the zone between intrusions of granitic magma bodies and carbonate sedimentary rocks such as limestone and dolostone. Hot fluids derived from the magma are rich in silica, iron, aluminium. These fluids mix in the zone, dissolve calcium-rich carbonate rocks. The resulting metamorphic rock may consist of a wide variety of minerals dependent largely on the original composition of the magmatic fluids. Skarns are sometimes associated with mineable accumulations of metallic ores of iron, copper, zinc, lead, gold, in such cases these deposits are called skarn deposits. Skarns are, in their broadest sense, formed by mass and chemical transport and they need not be igneous in origin, two adjacent sedimentary layers such as a banded iron formation and a limestone may react to exchange metals and fluids during metamorphism, creating a skarn. However, the widest use of the word is in describing the metasomatised zones of wall adjacent to granites. Skarns which are created by reaction between metamorphic-sedimentary layers are known as chemical skarns or skarnoids. Skarns must also be distinguished from calc-silicate hornfels, usually by field relationships, skarns of igneous origin are classified as exoskarns or endoskarns. Exoskarns occur at and outside the granite which produced them, and are alterations of wall rocks, typical skarn minerals include pyroxene, garnet, idocrase, wollastonite, actinolite, magnetite or hematite, and epidote. Often, feldspathoids and rare calc-silicates such as scapolite are found in marginal areas. Skarns are a class of rocks and are intimately associated with granite intrusions. Skarns are rarely seen with other types of granites, because of the fluid chemistry, s-type granites are more prone to generating late-stage fluid rich in silica, incompatible elements and halides because they are generally more potassic, oxidised and hydrous. Exoskarns are formed when fluids left over from the crystallisation of the granite are ejected from the mass at the stages of emplacement. When these fluids come into contact with rocks, usually carbonates such as limestone or dolostone. Because these fluids carry dissolved silica, iron, metals, halides and sulfur, uncommon types of skarns are formed in contact with sulfidic or carbonaceous rocks such as black shales, graphite shales, banded iron formations and, occasionally, salt or evaporites. Here, fluids react less via chemical exchange of ions, endoskarns are rarer, generally because the fluids created by a granite are usually formed in equilibrium with the minerals of the granite
30.
Volcanic rock
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Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin, for these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term volcanic is often applied to what are strictly metavolcanic rocks, Volcanic rocks are among the most common rock types on Earths surface, particularly in the oceans. On land, they are common at plate boundaries and in flood basalt provinces. It has been estimated that volcanic rocks cover about 8% of the Earths current land surface, lava Tephra Volcanic bomb Lapilli Volcanic ash Volcanic rocks are usually fine-grained or aphanitic to glass 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. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava, pumice is a highly vesicular rock produced in explosive volcanic eruptions. Most modern petrologists classify igneous rocks, including rocks, by their chemistry when dealing with their origin. The fact that different mineralogies and textures may be developed from the same initial magmas has led petrologists to rely heavily on chemistry to look at a volcanic rocks origin. The chemistry of volcanic rocks is dependent on two things, the composition of the primary magma and the subsequent differentiation. Differentiation of most volcanic rocks tends to increase the silica content, the initial composition of most volcanic rocks is basaltic, albeit small differences in initial compositions may result in multiple differentiation series. The most common of these series are tholeiitic, calc-alkaline, most volcanic rocks share a number of common minerals. Differentiation of volcanic rocks tends to increase the silica content mainly by fractional crystallization, thus, more evolved volcanic rocks tend to be richer in minerals with a higher amount if silica such as phyllo and tectosilicates including the feldspars, quartz polymorphs and muscovite. While still dominated by silicates, more volcanic rocks have mineral assemblages with less silica, such as olivine. Bowens reaction series correctly predicts the order of formation of the most common minerals in volcanic rocks, occasionally, a magma may pick up crystals that crystallized from another magma, these crystals are called xenocrysts. Diamonds found in kimberlites are rare but well-known xenocrysts, the kimberlites do not create the diamonds, Volcanic rocks are named according to both their chemical composition and texture. Basalt is a common volcanic rock with low silica content
31.
Rhombus
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In Euclidean geometry, a rhombus is a simple quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length, every rhombus is a parallelogram and a kite. A rhombus with right angles is a square, the word rhombus comes from Greek ῥόμβος, meaning something that spins, which derives from the verb ῥέμβω, meaning to turn round and round. The word was used both by Euclid and Archimedes, who used the term solid rhombus for two right circular cones sharing a common base, the surface we refer to as rhombus today is a cross section of this solid rhombus through the apex of each of the two cones. This is a case of the superellipse, with exponent 1. Every rhombus has two diagonals connecting pairs of vertices, and two pairs of parallel sides. Using congruent triangles, one can prove that the rhombus is symmetric across each of these diagonals and it follows that any rhombus has the following properties, Opposite angles of a rhombus have equal measure. The two diagonals of a rhombus are perpendicular, that is, a rhombus is an orthodiagonal quadrilateral, the first property implies that every rhombus is a parallelogram. Thus denoting the common side as a and the diagonals as p and q, not every parallelogram is a rhombus, though any parallelogram with perpendicular diagonals is a rhombus. In general, any quadrilateral with perpendicular diagonals, one of which is a line of symmetry, is a kite, every rhombus is a kite, and any quadrilateral that is both a kite and parallelogram is a rhombus. A rhombus is a tangential quadrilateral and that is, it has an inscribed circle that is tangent to all four sides. As for all parallelograms, the area K of a rhombus is the product of its base, the base is simply any side length a, K = a ⋅ h. The inradius, denoted by r, can be expressed in terms of the p and q as. The dual polygon of a rhombus is a rectangle, A rhombus has all sides equal, a rhombus has opposite angles equal, while a rectangle has opposite sides equal. A rhombus has a circle, while a rectangle has a circumcircle. A rhombus has an axis of symmetry through each pair of opposite vertex angles, the diagonals of a rhombus intersect at equal angles, while the diagonals of a rectangle are equal in length. The figure formed by joining the midpoints of the sides of a rhombus is a rectangle, a rhombohedron is a three-dimensional figure like a cube, except that its six faces are rhombi instead of squares. The rhombic dodecahedron is a polyhedron with 12 congruent rhombi as its faces
32.
Trachyte
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Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. It is the equivalent of syenite. The mineral assemblage consists of essential alkali feldspar, relatively minor plagioclase, biotite, clinopyroxene and olivine are common accessory minerals. Chemically, trachyte contains 60 to 65% silica content, less SiO2 than rhyolite and these chemical differences are consistent with the position of trachyte in the TAS classification, and they account for the feldspar-rich mineralogy of the rock type. Trachytes usually consist mainly of sanidine feldspar, very often they have minute irregular steam cavities which make the broken surfaces of specimens of these rocks rough and irregular, and from this character they have derived their name. The trachytes are often described as being the equivalents of the plutonic syenites. Rhomb porphyry is an example with usually large porphyritic rhomb shaped phenocrysts embedded in a very fine-grained matrix, quartz is typically rare in trachyte, but tridymite is by no means uncommon. They often cover the surfaces of the larger feldspars or line the cavities of the rock. In the older trachytes, secondary quartz is not rare, of the mafic minerals present, augite is the most common. It is usually of pale color, and its small crystals are often very perfect in form. Olivine is unusual, though found in some trachytes, like those of the Arso in Ischia, basic varieties of plagioclase, such as labradorite, are known also as phenocrysts in some Italian trachytes. Dark brown varieties of augite and rhombic pyroxene have been observed but are not common, apatite, zircon and magnetite are practically always present as accessory minerals. Trachytes, being rich in potassium feldspar, necessarily contain considerable amounts of alkali. Occasionally minerals of the group, such as nepheline, sodalite and leucite, occur. In many trachytes, however, the phenocrysts are few and small, the ferromagnesian minerals rarely occur in large crystals, and are usually not conspicuous in hand specimens of these rocks. Sometimes granular augite or spongy riebeckite occurs in the groundmass, trachytes are well represented among the Cenozoic volcanic rocks of Europe. In the neighborhood of Rome, Naples and the island of Ischia trachytic lavas, trachytes are also found on the island of Pantelleria. In the United States, trachytes crop out extensively in the Davis Mountains, Chisos Mountains, in England there are Permian trachytes in the Exeter district, and Carboniferous trachytes are found in many parts of the central valley of Scotland
33.
Latite
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Latite is an igneous, volcanic rock, with aphanitic-aphyric to aphyric-porphyritic texture. Its mineral assemblage is usually alkali feldspar and plagioclase in approximately equal amounts, quartz is less than five percent and is absent in a feldspathoid-bearing latite, and olivine is absent in a quartz-bearing latite. When quartz content is greater than five percent the rock is classified as quartz latite, biotite, hornblende, pyroxene and scarce olivine or quartz are common accessory minerals. Rhomb porphyries are a variety with gray-white porphyritic rhomb shaped phenocrysts embedded in a very fine grained red-brown matrix. The composition of rhomb porphyry places it in the trachyte - latite classification of the QAPF diagram, latite is found, for example, as lavas in Bulgaria and as intrusive laccoliths and sills in South Dakota, USA
34.
QAPF diagram
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A QAPF diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition. The acronym, QAPF, stands for Quartz, Alkali feldspar, Plagioclase and these are the mineral groups used for classification in QAPF diagram. Q, A, P and F percentages are normalized, QAPF diagrams were created by the International Union of Geological Sciences, Subcommission on the Systematics of Igneous Rocks fostered by Albert Streckeisen. Geologists worldwide accept the diagrams as a classification of igneous, especially plutonic rocks, QAPF diagrams are mostly used to classify plutonic rocks, but are also used to classify volcanic rocks if modal mineralogical compositions have been determined. QAPF diagrams are not used to classify pyroclastic rocks or volcanic rocks if modal mineralogical composition is not determined, TAS is also used if volcanic rock contains volcanic glass. QAPF diagrams are not used if mafic minerals make up more than 90% of the rock composition. An exact name can be only if the mineralogical composition is known. The QAPF diagram has four minerals or mineral groups chosen as important cornerstones of the classification and these are quartz, Alkali feldspars, plagioclase feldspars, and feldspathoids. F and Q for chemical reasons can not exist together in one plutonic rock, other minerals may and almost certainly occur in these rocks as well but they have no significance in this classification scheme. So, the diagram is actually composed of two ternary plots. To use the classification, the concentration of minerals must be known. For example, a rock that contains no alkali feldspar and no feldspathoids but contains lots of pyroxenes, plagioclase feldspar. This diagram does not determine whether a rock is gabbro, diorite, there are another criteria used to decide that. Note that this diagram is not used for all plutonic rocks, ultramafic rocks are the most important plutonic rocks that have separate classification diagrams. Classification and Nomenclature of Plutonic Rocks, Recommendations of the IUGS Subcommission on the Systematics of Igneous Rocks. IUGS Subcommission on the Systematics of Igneous Rocks, Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Melilite Rocks. Neues Jahrbuch für Mineralogie, Abhandlungen, Vol.141, 1-14, Igneous Rocks, A Classification and Glossary of Terms, Recommendations of International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Classification of Igneous Rocks - IUGS Classification, Geological Sciences Department - Cal Poly Pomona, archived from the original on 30 Sep 2011
35.
Lava
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Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is called lava. The molten rock is formed in the interior of planets, including Earth. The source of the heat melts the rock within the earth is geothermal energy. When first erupted from a vent, lava is a liquid usually at temperatures from 700 to 1,200 °C. A lava flow is an outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock, the term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic, explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word lava comes from Italian, and is derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma was apparently in an account written by Francesco Serao on the eruption of Vesuvius between May 14 and June 4,1737. Serao described a flow of lava as an analogy to the flow of water. The composition of almost all lava of the Earths crust is dominated by silicate minerals, mostly feldspars, olivine, pyroxenes, amphiboles, micas, igneous rocks, which form lava flows when erupted, can be classified into three chemical types, felsic, intermediate, and mafic. These classes are primarily chemical, however, the chemistry of lava also tends to correlate with the temperature, its viscosity. Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, most silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. Felsic magmas can erupt at temperatures as low as 650 to 750 °C, unusually hot rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, and usually somewhat richer in magnesium, intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, and also commonly hotter, greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950 °C
36.
Rift
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In geology, a rift is a linear zone where the Earths crust and lithosphere are being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben with normal faulting, where rifts remain above sea level they form a rift valley, which may be filled by water forming a rift lake. The axis of the area may contain volcanic rocks, and active volcanism is a part of many. Major rifts occur along the axis of most mid-ocean ridges. Failed rifts are the result of rifting that failed to continue to the point of break-up. Typically the transition from rifting to spreading develops at a junction where three converging rifts meet over a hotspot. Two of these evolve to the point of spreading, while the third ultimately fails. Most rifts consist of a series of segments that together form the linear zone characteristic of rifts. The individual rift segments have a dominantly half-graben geometry, controlled by a single basin-bounding fault, segment lengths vary between rifts, depending on the elastic thickness of the lithosphere. Areas of thick colder lithosphere, such as the Baikal Rift have segment lengths in excess of 80 km, while in areas of warmer thin lithosphere, segment lengths may be less than 30 km. Along the axis of the rift the position, and in cases the polarity. Segment boundaries often have a complex structure and generally cross the rift axis at a high angle. These segment boundary zones accommodate the differences in fault displacement between the segments and are known as accommodation zones. Accommodation zones may be located where older crustal structures intersect the rift axis, in the Gulf of Suez rift, the Zaafarana accommodation zone is located where a shear zone in the Arabian-Nubian Shield meets the rift. At the onset of rifting, the part of the lithosphere starts to extend on a series of initially unconnected normal faults. In subaerial rifts, drainage at this stage is generally internal, as the rift evolves, some of the individual fault segments grow, eventually becoming linked together to form the larger bounding faults. Subsequent extension becomes concentrated on these faults, the longer faults and wider fault spacing leads to more continuous areas of fault-related subsidence along the rift axis. Significant uplift of the rift shoulders develops at this stage, strongly influencing drainage, during rifting, as the crust is thinned, the Earths surface subsides and the Moho becomes correspondingly raised
37.
East African Rift
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The East African Rift is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago, in the past, it was considered to be part of a larger Great Rift Valley that extended north to Asia Minor. As extension continues, lithospheric rupture will occur within 10 million years, the Somalian plate will break off, a series of distinct rift basins, the East African Rift System extends over thousands of kilometers. The EAR consists of two main branches, the Eastern Rift Valley includes the Main Ethiopian Rift, running eastward from the Afar Triple Junction, which continues south as the Kenyan Rift Valley. The Western Rift Valley includes the Albertine Rift, and farther south, to the north of the Afar Triple Junction, the rift follows one of two paths, west to the Red Sea Rift or east to the Aden Ridge in the Gulf of Aden. The EAR runs from the Afar Triple Junction in the Afar Triangle of Ethiopia through eastern Africa, the EAR transects through Ethiopia, Kenya, Uganda, Rwanda, Burundi, Zambia, Tanzania, Malawi and Mozambique. The Davie Ridge ranges between 30–120 km wide, with a west facing scarp along the half of its length that rises up to 2300 m above the sea floor. Its movement is concurrent with the EAR, over time, many theories have tried to clarify the evolution of the East African Rift. In 1972 it was proposed that the EAR was not caused by tectonic activity, others proposed an African superplume causing mantle deformation. However, the varying geochemical signatures of a suite of Ethiopian lavas suggest multiple plume sources, at least one of deep mantle origin, additionally, the subject of deep-rooted mantle plumes is still a matter of controversy, and therefore cannot be confirmed. The most recent and accepted view is the theory put forth in 2009, at that time it was suggested that lithospheric thinning generated volcanic activity, further increasing the magmatic processes at play such as intrusions and numerous small plumes. These processes further thin the lithosphere in saturated areas, forcing the thinning lithosphere to behave like a mid-ocean ridge, prior to rifting, enormous continental flood basalts erupted on the surface and uplift of the Ethiopian, Somalian, and East African plateaus occurred. The first stage of rifting of the EAR is characterized by rift localization, periods of extension alternated with times of relative inactivity. There was also the reactivation of a weakness in the crust, a suture zone of multiple cratons, displacement along large boundary faults. The second stage of rifting is characterized by the deactivation of large boundary faults, the development of internal fault segments, today, the narrow rift segments of the East African Rift system form zones of localized strain. These rifts are the result of the actions of numerous faults which are typical of all tectonic rift zones. The African continental crust is generally cool and strong, many cratons are found throughout the EAR, such as the Tanzania and Kaapvaal cratons. The cratons are thick, and have survived for billions of years with little tectonic activity and they are characterized by greenstone belts, tonalites, and other high-grade metamorphic lithologies
38.
Mount Kilimanjaro
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Mount Kilimanjaro, with its three volcanic cones, Kibo, Mawenzi, and Shira, is a dormant volcano in Tanzania. It is the highest mountain in Africa, and rises approximately 4,900 m from its base to 5,895 metres above sea level, the first recorded ascent to the summit of the mountain was by Hans Meyer and Ludwig Purtscheller in 1889. The mountain is part of the Kilimanjaro National Park and is a major climbing destination, the mountain has been the subject of many scientific studies because of its shrinking glaciers. Kilimanjaro rises approximately 4,900 m from its base in the plains near the municipality of Moshi to its summit height of 5,895 metres. Kilimanjaro is the highest volcano outside South America, Kilimanjaro is a large stratovolcano and is composed of three distinct volcanic cones, Kibo, the highest, Mawenzi at 5,149 metres, and Shira, the shortest at 4,005 metres. Mawenzi and Shira are extinct, while Kibo is dormant and could erupt again, Uhuru Peak is the highest summit on Kibos crater rim. The Tanzania National Parks Authority, a Tanzanian governmental agency, and that height is based on a British Ordnance Survey in 1952. Since then, the height has been measured as 5,892 metres in 1999,5,891 metres in 2008, the interior of the volcanic edifice is poorly known, given the lack of large scale erosion that could have exposed the interiors of the volcano. Shira is topped by a plateau at 3,800 metres. The remnant caldera rim has been degraded deeply by erosion, before the caldera formed and erosion began, Shira might have been between 4,900 m and 5,200 m high. It is mostly composed of lavas with some pyroclastics. The formation of the caldera was accompanied by lava emanating from ring fractures, two cones formed subsequently, the phonolitic one at the northwest end of the ridge and the doleritic Platzkegel in the caldera centre. Both Mawenzi and Kibo began erupting about 1 million years ago and they are separated by the Saddle Plateau at 4,400 metres elevation. The youngest dated rocks at Mawenzi are about 448,000 years old, Mawenzi forms a horseshoe shaped ridge with pinnacles and ridges opening to the northeast which has a tower like shape resulting from deep erosion and a mafic dyke swarm. Several large cirques cut into the ring, the largest of these sits on top of the Great Barranco gorge, also notable are the Ost and West Barrancos on the northeastern side of the mountain. Most of the side of the mountain has been removed by erosion. Mawenzi has a peak named Neumann Tower. Kibo is the largest cone and is more than 15 miles wide at the Saddle Plateau altitude, the last activity here has been dated to between 150,000 and 200,000 years ago and created the current Kibo summit crater
39.
Mount Erebus
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Mount Erebus is the second-highest volcano in Antarctica and the southernmost active volcano on Earth. It is the sixth highest ultra mountain on an island, with a summit elevation of 3,794 metres, it is located on Ross Island, which is also home to three inactive volcanoes, Mount Terror, Mount Bird, and Mount Terra Nova. The volcano has been active since c.1.3 million years ago and is the site of the Mount Erebus Volcano Observatory run by the New Mexico Institute of Mining and Technology. Mount Erebus is currently the most active volcano in Antarctica and is the current eruptive zone of the Erebus hotspot, the summit contains a persistent convecting phonolitic lava lake, one of five long-lasting lava lakes on Earth. Characteristic eruptive activity consists of Strombolian eruptions from the lake or from one of several subsidiary vents. Scientific study of the volcano is also facilitated by their proximity to McMurdo Station and Scott Base, Mount Erebus is classified as a polygenetic stratovolcano. The bottom half of the volcano is a shield and the top half is a stratocone, the composition of the current eruptive products of Erebus is anorthoclase-porphyritic tephritic phonolite and phonolite, which are the bulk of exposed lava flow on the volcano. The oldest eruptive products consist of relatively undifferentiated and non-viscous basanite lavas that form the low broad platform shield of Erebus, slightly younger basanite and phonotephrite lavas crop out on Fang Ridge—an eroded remnant of an early Erebus volcano—and at other isolated locations on the flanks of Erebus. Erebus is the only presently erupting phonolite volcano. Lava flows of more viscous phonotephrite and trachyte erupted after the basanite, the upper slopes of Mount Erebus are dominated by steeply dipping tephritic phonolite lava flows with large scale flow levees. A conspicuous break in slope at approximately 3,200 metres calls attention to a summit plateau representing a caldera, the summit caldera was created by an explosive VEI-6 eruption that occurred 18,000 ±7,000 years ago. It is filled with small volume tephritic phonolite and phonolite lava flows, in the center of the summit caldera is a small steep-sided cone composed primarily of decomposed lava bombs and a large deposit of anorthoclase crystals known as Erebus crystals. The active lava lake in this summit cone undergoes continuous degassing and these results demonstrated a complex upper-volcano conduit system with appreciable upper-volcano magma storage to the northwest of the lava lake at depths hundreds of meters below the surface. Mt. Erebus is notable for its numerous ice fumaroles – ice towers that form around gases that escape from vents in the surface. The ice caves associated with the fumaroles are dark, in alpine environments starved in organics. The life is sparse, mainly bacteria and fungi and this makes it of special interest for studying oligotrophs – organisms that can survive on minimal amounts of resources. It is thought that ice caves may exist on Mars – ice preserved under the surface in cave systems protected from the surface conditions. The caves on Erebus are of especial interest for astrobiology as most surface caves are influenced by human activities, the caves at Erebus are high altitude, yet accessible for study
40.
Ross Sea
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The Ross Sea is a deep bay of the Southern Ocean in Antarctica, between Victoria Land and Marie Byrd Land. It derives its name from the British explorer James Ross who visited this area in 1841. To the west of the sea lies Ross Island and to the east Roosevelt Island, while the southernmost part is covered by the Ross Ice Shelf, the underlying rocks are of upper Precambrian to lower Paleozoic age and are partly composed of calcium carbonate. The circulation of the Ross Sea is dominated by an ocean gyre. The circumpolar deep water current is a warm, salty. The Ross Sea is covered with ice for most of the year, the nutrient-laden water supports an abundance of plankton and this encourages a rich marine fauna. At least ten species, six bird species and 95 fish species are found here, as well as many invertebrates. New Zealand has claimed that the sea comes under their jurisdiction as part of the Ross Dependency, Marine biologists consider the sea to have a high level of biological diversity and it is the site of much scientific research. It is also the focus of some environmentalist groups who have campaigned to have the area proclaimed as a marine reserve. The Ross Sea was discovered by James Ross in 1841, in the west of the Ross Sea is Ross Island with the Mt. Erebus volcano, in the east Roosevelt Island. The southern part is covered by the Ross Ice Shelf, roald Amundsen started his South Pole expedition in 1911 from the Bay of Whales, which was located at the shelf. In the west of the Ross sea, McMurdo Sound is a port which is free of ice during the summer. The southernmost part of the Ross Sea is Gould Coast, which is two hundred miles from the Geographic South Pole. All land masses in the Ross Sea are claimed by New Zealand to fall under the jurisdiction of the Ross Dependency, a 10-metre long colossal squid weighing 495 kilograms was captured in the Ross Sea on February 22,2007. Ross System rocks are of upper Precambrian to lower Paleozoic age and these miogeosyncline metasedimentary rocks are usually folded about northwest and southeast axes and are partly composed of calcium carbonate, often including limestone. Groups within the Ross System include the Robertson Bay Group, Priestley Group, Skelton Group, Beardmore Group, Byrd Group, Queen Maud Group, the Robertson Bay Group ranges from 56 to 76% silica and compares closely with other Ross System members. The Priestley Group rocks are similar to those of the Robertson Bay Group and include dark slates, argillites, siltstones and they can be found near the Priestley and Campbell glaciers. For thirty miles along the lower Skelton Glacier are the calcareous greywackes and argillites of the Skelton Group, the region between the lower Beardmore Glacier and the lower Shackelton Glacier sits the Beardmore Group
41.
Antarctica
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It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 14,000,000 square kilometres, it is the fifth-largest continent, for comparison, Antarctica is nearly twice the size of Australia. About 98% of Antarctica is covered by ice that averages 1.9 km in thickness, Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Antarctica is a desert, with precipitation of only 200 mm along the coast. The temperature in Antarctica has reached −89.2 °C, though the average for the quarter is −63 °C. Anywhere from 1,000 to 5,000 people reside throughout the year at the research stations scattered across the continent. Organisms native to Antarctica include many types of algae, bacteria, fungi, plants, protista, vegetation, where it occurs, is tundra. The continent, however, remained neglected for the rest of the 19th century because of its hostile environment, lack of easily accessible resources. In 1895, the first confirmed landing was conducted by a team of Norwegians, Antarctica is a de facto condominium, governed by parties to the Antarctic Treaty System that have consulting status. Twelve countries signed the Antarctic Treaty in 1959, and thirty-eight have signed it since then, the treaty prohibits military activities and mineral mining, prohibits nuclear explosions and nuclear waste disposal, supports scientific research, and protects the continents ecozone. Ongoing experiments are conducted by more than 4,000 scientists from many nations, the name Antarctica is the romanised version of the Greek compound word ἀνταρκτική, feminine of ἀνταρκτικός, meaning opposite to the Arctic, opposite to the north. Aristotle wrote in his book Meteorology about an Antarctic region in c.350 B. C, marinus of Tyre reportedly used the name in his unpreserved world map from the 2nd century A. D. Before acquiring its present geographical connotations, the term was used for locations that could be defined as opposite to the north. For example, the short-lived French colony established in Brazil in the 16th century was called France Antarctique, the first formal use of the name Antarctica as a continental name in the 1890s is attributed to the Scottish cartographer John George Bartholomew. Antarctica has no population and there is no evidence that it was seen by humans until the 19th century. Explorer Matthew Flinders, in particular, has credited with popularising the transfer of the name Terra Australis to Australia. Cook came within about 120 km of the Antarctic coast before retreating in the face of ice in January 1773. The first confirmed sighting of Antarctica can be narrowed down to the crews of ships captained by three individuals, according to various organisations, ships captained by three men sighted Antarctica or its ice shelf in 1820, von Bellingshausen, Edward Bransfield, and Nathaniel Palmer
42.
Norway
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The Antarctic Peter I Island and the sub-Antarctic Bouvet Island are dependent territories and thus not considered part of the Kingdom. Norway also lays claim to a section of Antarctica known as Queen Maud Land, until 1814, the kingdom included the Faroe Islands, Greenland, and Iceland. It also included Isle of Man until 1266, Shetland and Orkney until 1468, Norway has a total area of 385,252 square kilometres and a population of 5,258,317. The country shares a long border with Sweden. Norway is bordered by Finland and Russia to the north-east, Norway has an extensive coastline, facing the North Atlantic Ocean and the Barents Sea. King Harald V of the Dano-German House of Glücksburg is the current King of Norway, erna Solberg became Prime Minister in 2013, replacing Jens Stoltenberg. A constitutional monarchy, Norway divides state power between the Parliament, the Cabinet and the Supreme Court, as determined by the 1814 Constitution, the kingdom is established as a merger of several petty kingdoms. By the traditional count from the year 872, the kingdom has existed continuously for 1,144 years, Norway has both administrative and political subdivisions on two levels, counties and municipalities. The Sámi people have an amount of self-determination and influence over traditional territories through the Sámi Parliament. Norway maintains close ties with the European Union and the United States, the country maintains a combination of market economy and a Nordic welfare model with universal health care and a comprehensive social security system. Norway has extensive reserves of petroleum, natural gas, minerals, lumber, seafood, the petroleum industry accounts for around a quarter of the countrys gross domestic product. On a per-capita basis, Norway is the worlds largest producer of oil, the country has the fourth-highest per capita income in the world on the World Bank and IMF lists. On the CIAs GDP per capita list which includes territories and some regions, from 2001 to 2006, and then again from 2009 to 2017, Norway had the highest Human Development Index ranking in the world. It also has the highest inequality-adjusted ranking, Norway ranks first on the World Happiness Report, the OECD Better Life Index, the Index of Public Integrity and the Democracy Index. Norway has two names, Noreg in Nynorsk and Norge in Bokmål. The name Norway comes from the Old English word Norðrveg mentioned in 880, meaning way or way leading to the north. In contrasting with suðrvegar southern way for Germany, and austrvegr eastern way for the Baltic, the Anglo-Saxon of Britain also referred to the kingdom of Norway in 880 as Norðmanna land. This was the area of Harald Fairhair, the first king of Norway, and because of him
43.
Portrait of the Four Tetrarchs
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The Portrait of the Four Tetrarchs is a porphyry sculpture group of four Roman emperors dating from around 300 AD. Since the Middle Ages it has fixed to a corner of the façade of St Marks Basilica in Venice. It probably originally formed part of the decorations of the Philadelphion in Constantinople, the Roman Empire was for a time after 293 ruled by a tetrarchy, instituted by Emperor Diocletian. The tetrarchy consisted of two Augusti and two Caesars, the empire was territorially divided into western and eastern halves, with a senior and a junior emperor in each half. After Diocletian and his colleague, Maximian, retired in 305, the system finally ceased to exist around 313. The Portrait of the Four Tetrarchs symbolizes the concept of the tetrarchy, each tetrarch looks the same, without any individualized characteristics, except that two, probably representing the older Augusti, have beards, and two do not who might have symbolized the Caesars. The group is divided into pairs, each embracing, which unites Augusti, the overall effect suggests unity and stability. The very choice of material, the durable porphyry, symbolizes a permanence of the kind reminiscent of Egyptian statuary, porphyry was rare and reserved for imperial use. The figures are stout and blocky, far from the verisimilitude or the idealism of earlier Greco-Roman art, the figures are stiff and rigid, the attire being patterned and stylized. Their faces are repetitive and they seem to stare in a kind of trance, the question of how to account for what may seem a decline in both style and execution in Late Antique art has generated a vast amount of discussion. One factor that cannot be responsible, as the date and origin of the Portrait of the Four Tetrarchs show, is the rise of Christianity to official support and this shift in artistic style points towards the style of the Middle Ages. The statues probably originally decorated the columns of the porch of the Philadelphion in Constantinople and they were plundered by the Venetians when the city was sacked during the Fourth Crusade in 1204 and brought to Venice. In the 1960s, the part of the missing foot was discovered by archaeologists in Istanbul close to the Bodrum Mosque. This part is in the Istanbul Archaeology Museum, a different story is told by The Travels of Marco Polo, the famous Venetians autobiography put to paper with the help of his co-writer, Rustichello of Pisa, around 1300. It began in a quarrel about an old church called St. Sabbas, which stood on the common boundary of the Venetian and Genoese estates in Acre. Venice at this time kept the upper hand, beating Genoa by land and sea. Four ancient porphyry figures from St. Sabbas were sent in triumph to Venice, reconstruction of the Philadelphion, where the sculpture used to stand
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Philadelphion
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The Philadelphion was a public square located in Constantinople. After passing the Forum of Theodosius, the Mese Odos branched into two directions, one led to the quarter known today as Yedikule, via the Aksaray and Cerrahpaşa quarters. The other passed through the quarters of Şehzadebaşı and Fatih until reaching the quarter of Edirnekapı, the space where the road forked was thought to be the physical centre, or mesomphalos, of the city. Perhaps this was a statue of Constantines sister Anastasia, the Patria of Constantinople furthermore records that statues of two sons of Constantine seated on thrones stood opposite from the column. These statues apparently survived until the early 15th century, when they were known as the True Judges. In 1958, P. Cameron, Averil, Herrin, Judith, Constantinople in the Early Eighth Century. The Parastaseis Syntomoi Chronikai, Introduction, Translation, and Commentary, I due gruppi in porfiro di San Marco in Venezia ed il Philadelphion in Costantinopoli. Tentative reconstruction of the site at the Byzantium 1200 project
