An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities; the seismicity, or seismic activity, of an area is the frequency and size of earthquakes experienced over a period of time. The word tremor is used for non-earthquake seismic rumbling. At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground; when the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can trigger landslides, volcanic activity. In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused by rupture of geological faults, but by other events such as volcanic activity, mine blasts, nuclear tests.
An earthquake's point of initial rupture is called its hypocenter. The epicenter is the point at ground level directly above the hypocenter. Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane; the sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface; this continues until the stress has risen sufficiently to break through the asperity allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, cracking of the rock, thus causing an earthquake.
This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior. There are three main types of fault, all of which may cause an interplate earthquake: normal and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas.
Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip. Reverse faults those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including all of those of magnitude 8 or more. Strike-slip faults continental transforms, can produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are less than magnitude 7. For every unit increase in magnitude, there is a thirtyfold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases 30 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 900 times more energy than a 5.0 magnitude of earthquake. An 8.6 magnitude earthquake releases the same amount of energy as 10,000 atomic bombs like those used in World War II. This is so because the energy released in an earthquake, thus its magnitude, is proportional to the area of the fault that ruptures and the stress drop.
Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The topmost, brittle part of the Earth's crust, the cool slabs of the tectonic plates that are descending down into the hot mantle, are the only parts of our planet which can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 °C flow in response to stress; the maximum observed lengths of ruptures and mapped faults are 1,000 km. Examples are the earthquakes in Chile, 1960; the longest earthquake ruptures on strike-slip faults, like the San Andreas Fault, the North Anatolian Fault in Turkey and the Denali Fault in Alaska, are about half to one third as long as the lengths along subducting plate margins, those along normal faults are shorter. The most important parameter controlling the maximum earthquake magnitude on a fault is however not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins, the dip angle of the rupture plane is shallow about 10 de
Pozzuoli is a city and comune of the Metropolitan City of Naples, in the Italian region of Campania. It is the main city of the Phlegrean Peninsula. Pozzuoli began as the Greek colony of Dicaearchia; the Roman colony was established in 194 BC, took the name Puteoli which it has his roots from'puteus', meaning well and'osco fistulus'. An alternative etymology of Puteoli from the Latin puteo, referring to the sulfuric smell in the area, most notably from Solfatara; this is because Pozzuoli lies in the center of a volcanic caldera. Puteoli was the great emporium for the Alexandrian grain ships, other ships from all over the Roman world, it was the main hub for goods exported from Campania, including blown glass, wrought iron, marble. The Roman naval base at nearby Misenum housed the largest naval fleet in the ancient world, it was the site of the Roman Dictator Sulla's country villa and the place where he died in 78 BC. Pliny mentions Pozzuoli as the site of a famed cochlearium created by Fulvius Hirpinus, known for raising exquisite snails.
The local volcanic sand, pozzolana formed the basis for the first effective concrete, as it reacted chemically with water. Instead of just evaporating off, the water would turn this sand/lime mix into a mortar strong enough to bind lumps of aggregate into a load-bearing unit; this made possible the cupola of the Pantheon, still the world's largest unreinforced concrete dome. The apostle Paul landed here on his way from which it was 170 miles distant. Here he stayed for seven days and began with his companions his journey by the Appian Way to Rome. Puteoli is considered the best candidate for the unnamed city where the 1st century Roman novel Satyricon takes place. In 37 AD Puteoli was the location for a political stunt by Emperor Gaius Caligula, who on becoming Emperor ordered a temporary floating bridge to be built using trading vessels, stretching for over two miles from the town to the famous neighboring resort of Baiae, across which he proceeded to ride his horse, in defiance of an astrologer's prediction that he had "no more chance of becoming Emperor than of riding a horse across the Gulf of Baiae".
Saint Proculus was martyred here with his companions in the fourth century, is the city's patron saint. The seven eagle heads on the coat-of-arms for the town of Pozzuoli are said to represent seven of these martyrs. November 16 was the official feast day for Saint Proculus. St. Proculus was affectionately nicknamed'u pisciasotto because November 16 was a day of rain; the townspeople celebrated his feast day on the second Sunday in May. Charles Lyell studied the Macellum columns. Since 1946 the town has been the home of the Accademia Aeronautica, the Italian Air Force Academy, first situated on the island of Nisida from 1962 on a purpose-built hilltop campus overlooking the bay. From August 1982 to December 1984 the city experienced hundreds of tremors and bradyseismic activity which reached a peak on October 4, 1983, damaging 8,000 buildings in the city center and dislocating 36,000 people, many permanently; the events raised the sea bottom by 2 m, rendered the Bay of Pozzuoli too shallow for large craft.
The town's attractions include: The Macellum of Pozzuoli known as the Temple of Serapis or serapeum, is considered the city's symbol. The "temple" was a marketplace, its name derives from the misinterpretation of its function after a statue of the god Serapis was found in 1750 at this location. The Macellum includes three majestic columns in Cipollino marble, which show erosion from marine Lithophaga molluscs when, at an earlier time, the ground level was much lower due to Bradyseism, sea-water could flow in. Flavian Amphitheater, the third largest Italian amphitheater after the Colosseum and the Capuan Amphitheater. Solfatara Forum Minor Amphitheater near to the Flavian one, its remains were absorbed by other buildings, but some arches can be seen by Via Solfatara and Via Vigna, it is crossed by metropolitan railway and the arena is still buried Puteoli's Baths, so called Temple of Neptune, the remains of a big thermal complex now in Corso Terracciano which included "Dianae Nymphaeum", this last one hidden by buildings.
Villa Avellino, one of the few urban parks of Pozzuoli. It shows several Roman ruins and water tanks. There is a still working Roman "face" water fountain. Rione Terra, the first settlement of Puteoli Dicearkia in Greek, it is a multi-layered city with several Roman buildings. Sanctuary of San Gennaro. With the Cathedral of Naples, it is one of the two places in which the alleged miracle of the liquefaction of the saint's blood occurs. Lake Avernus, in which Virgil, in the 6th book of his Aeneid, placed the entrance to Hell; the name derives from Greek, means "Without Birds", referring to the absence of birds due to the sulfur gas that sprung fr
Aluminium or aluminum is a chemical element with symbol Al and atomic number 13. It is a silvery-white, soft and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; the chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. Aluminium is remarkable for its low density and its ability to resist corrosion through the phenomenon of passivation. Aluminium and its alloys are vital to the aerospace industry and important in transportation and building industries, such as building facades and window frames; the oxides and sulfates are the most useful compounds of aluminium. Despite its prevalence in the environment, no known form of life uses aluminium salts metabolically, but aluminium is well tolerated by plants and animals; because of these salts' abundance, the potential for a biological role for them is of continuing interest, studies continue.
Of aluminium isotopes, only 27Al is stable. This is consistent with aluminium having an odd atomic number, it is the only aluminium isotope that has existed on Earth in its current form since the creation of the planet. Nearly all the element on Earth is present as this isotope, which makes aluminium a mononuclidic element and means that its standard atomic weight equates to that of the isotope; the standard atomic weight of aluminium is low in comparison with many other metals, which has consequences for the element's properties. All other isotopes of aluminium are radioactive; the most stable of these is 26Al and therefore could not have survived since the formation of the planet. However, 26Al is produced from argon in the atmosphere by spallation caused by cosmic ray protons; the ratio of 26Al to 10Be has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, sediment storage, burial times, erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of 3s23p1, with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Aluminium can easily surrender its three outermost electrons in many chemical reactions; the electronegativity of aluminium is 1.61. A free aluminium atom has a radius of 143 pm. With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure, aluminium atoms form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; this crystal system is shared by some other metals, such as copper. Aluminium metal, when in quantity, is shiny and resembles silver because it preferentially absorbs far ultraviolet radiation while reflecting all visible light so it does not impart any color to reflected light, unlike the reflectance spectra of copper and gold.
Another important characteristic of aluminium is its low density, 2.70 g/cm3. Aluminium is a soft, lightweight and malleable with appearance ranging from silvery to dull gray, depending on the surface roughness, it is nonmagnetic and does not ignite. A fresh film of aluminium serves as a good reflector of visible light and an excellent reflector of medium and far infrared radiation; the yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has stiffness of steel, it is machined, cast and extruded. Aluminium atoms are arranged in a face-centered cubic structure. Aluminium has a stacking-fault energy of 200 mJ/m2. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity, with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.
Aluminium is the most common material for the fabrication of superconducting qubits. Aluminium's corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the bare metal is exposed to air preventing further oxidation, in a process termed passivation; the strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. This corrosion resistance is reduced by aqueous salts in the presence of dissimilar metals. In acidic solutions, aluminium reacts with water to form hydrogen, in alkaline ones to form aluminates—protective passivation under these conditions is negligible; because it is corroded by dissolved chlorides, such as common sodium chloride, household plumbing is never made from aluminium. However, because
Travertine is a form of limestone deposited by mineral springs hot springs. Travertine has a fibrous or concentric appearance and exists in white, cream-colored, rusty varieties, it is formed by a process of rapid precipitation of calcium carbonate at the mouth of a hot spring or in a limestone cave. In the latter, it can form stalactites and other speleothems, it is used in Italy and elsewhere as a building material. Travertine is a terrestrial sedimentary rock, formed by the precipitation of carbonate minerals from solution in ground and surface waters, and/or geothermally heated hot-springs. Similar deposits formed from ambient-temperature water are known as tufa; the word'travertine' is derived from the Italian travertino, itself a derivation of the Latin tiburtinus'of Tibur'. Its namesake is the origin of Tivoli, a district near Rome. Modern travertine is formed from geothermally heated supersaturated alkaline waters, with raised pCO2. On emergence, waters degas CO2 due to the lower atmospheric pCO2, resulting in an increase in pH.
Since carbonate solubility decreases with increased pH, precipitation is induced. Precipitation may be enhanced by factors leading to a reduction in pCO2, for example increased air-water interactions at waterfalls may be important, as may photosynthesis. Precipitation may be enhanced by evaporation in some springs. Both calcite and aragonite are found in hot spring travertines; when pure and fine, travertine is white, but it is brown to yellow due to impurities. Travertine may precipitate out directly onto rock and other inert materials as in Pamukkale or Mammoth Hot Springs for example. In Italy, well-known travertine quarries exist in Tivoli and Guidonia Montecelio, where the most important quarries since Ancient Roman times can be found; the Guidonia quarry has major historic value, as it was one of the quarries where Gian Lorenzo Bernini selected material from which to build the famous Colonnade of St. Peter's Square in Rome in 1656-1667. Michaelangelo chose travertine as the material for the external ribs of the dome of St Peter's Basilica.
Travertine derives its name from the former town, known as Tibur in ancient Roman times. The ancient name for the stone was lapis tiburtinus, meaning tibur stone, corrupted to travertino. Detailed studies of the Tivoli and Guidonia travertine deposits revealed diurnal and annual rhythmic banding and laminae, which have potential use in geochronology. Cascades of natural lakes formed behind travertine dams can be seen in Pamukkale, a UNESCO World Heritage Site. Other places with such cascades include Huanglong in Sichuan Province of China, the Mammoth Hot Springs in the US, Egerszalók in Hungary, Abbass Abad, Atash Kooh, Badab-e Surt in Iran, Band-i-Amir in Afghanistan, Lagunas de Ruidera, Hierve el Agua, Oaxaca and Semuc Champey, Guatemala. In Central Europe's last post-glacial palaeoclimatic optimum, huge deposits of tufa formed from karst springs. Important geotopes are found at the Swabian Alb in valleys at the foremost northwest ridge of the cuesta. On a smaller scale, these karst processes are still working.
Travertine has been an important building material since the Middle Ages. Travertine has formed sixteen huge, natural dams in a valley in Croatia known as Plitvice Lakes National Park. Clinging to moss and rocks in the water, the travertine has built up over several millennia to form waterfalls up to 70 m in height. In the U. S. the most well-known place for travertine formation is Yellowstone National Park, where the geothermal areas are rich in travertine deposits. Wyoming has travertines in Hot Springs State Park in Thermopolis. Oklahoma has two parks dedicated to this natural wonder. Turner Falls, the tallest waterfall in Oklahoma, is a 77 feet cascade of spring water flowing over a travertine cave. Honey Creek creates miles of travertine shelves both up and downstream. Many small waterfalls upstream in the dense woods repeat the travertine-formation effect; the city of Davis has made it a tourist attraction. Another travertine resource is in Oklahoma, 10 miles east of Turner Falls. Travertine Creek flows through a spring-water nature preserve within the boundaries of the Chickasaw National Recreation Area.
In Texas, the city of Austin and its surrounding "Hill Country" to the south is built on limestone. The area has many travertine formations, such as those found at Gorman Falls within Colorado Bend State Park, the nature preserve known as Hamilton Pool, the West Cave Preserve, Krause Springs in Spicewood. Hanging Lake in Glenwood Canyon in Colorado has aqua blue water. Rifle Falls State Park in Colorado features a triple waterfall over a travertine dam. In Arizona, on the south side of the Grand Canyon there is the Havasupai Reservation. Flowing through it is Havasu Creek, which has extensive travertine deposits. Three major waterfalls, Navajo Falls, Havasu Falls, Mooney Falls, are all located downstream from the town of Supai. There are numerous smaller cataracts formed by travertine dams; these features are located about 2 miles from Supai Village, are accessible by foot or horseback. In Iceland, the Hva
Marcus Vitruvius Pollio known as Vitruvius, was a Roman author, civil engineer and military engineer during the 1st century BC, known for his multi-volume work entitled De architectura. His discussion of perfect proportion in architecture and the human body led to the famous Renaissance drawing by Leonardo da Vinci of Vitruvian Man. By his own description Vitruvius served as an artilleryman, the third class of arms in the military offices, he served as a senior officer of artillery in charge of doctores ballistarum and libratores who operated the machines. Little is known about Vitruvius' life. Most inferences about him are extracted from his only surviving work De Architectura, his first name Marcus and his cognomen Pollio are uncertain. Marcus Cetius Faventinus writes of "Vitruvius Polio aliique auctores". An inscription in Verona, which names a Lucius Vitruvius Cordo, an inscription from Thilbilis in North Africa, which names a Marcus Vitruvius Mamurra have been suggested as evidence that Vitruvius and Mamurra were from the same family.
Neither association, however, is borne out by De Architectura, nor by the little, known of Mamurra. Vitruvius was a military engineer, or a praefect architectus armamentarius of the apparitor status group, he is mentioned in Pliny the Elder's table of contents for Naturalis Historia, in the heading for mosaic techniques. Frontinus refers to "Vitruvius the architect" in his late 1st-century work De aquaeductu. Born a free Roman citizen, by his own account, Vitruvius served in the Roman army under Caesar with the otherwise poorly identified Marcus Aurelius, Publius Minidius, Gnaeus Cornelius; these names vary depending on the edition of De architectura. Publius Minidius is written as Publius Numidicus and Publius Numidius, speculated as the same Publius Numisius inscribed on the Roman Theatre at Heraclea; as an army engineer he specialized in the construction of ballista and scorpio artillery war machines for sieges. It is speculated; the locations where he served can be reconstructed from, for example, descriptions of the building methods of various "foreign tribes".
Although he describes places throughout De Architectura, he does not say. His service included north Africa, Hispania and Pontus. To place the role of Vitruvius the military engineer in context, a description of "The Prefect of the camp" or army engineer is quoted here as given by Flavius Vegetius Renatus in The Military Institutions of the Romans: The Prefect of the camp, though inferior in rank to the, had a post of no small importance; the position of the camp, the direction of the entrenchments, the inspection of the tents or huts of the soldiers and the baggage were comprehended in his province. His authority extended over the sick, the physicians who had the care of them, he had the charge of providing carriages and the proper tools for sawing and cutting wood, digging trenches, raising parapets, sinking wells and bringing water into the camp. He had the care of furnishing the troops with wood and straw, as well as the rams, onagri and all the other engines of war under his direction; this post was always conferred on an officer of great skill and long service, and, capable of instructing others in those branches of the profession in which he had distinguished himself.
At various locations described by Vitruvius and sieges occurred. He is the only source for the siege of Larignum in 56 BC. Of the battlegrounds of the Gallic War there are references to: the siege and massacre of the 40,000 residents at Avaricum in 52 BC; the broken siege at Gergovia in 52 BC. The circumvallation and Battle of Alesia in 52 BC, and the siege of Uxellodunum in 51 BC. These are all sieges of large Gallic oppida. Of the sites involved in Caesar's civil war, we find the Siege of Massilia in 49 BC, the Battle of Dyrrhachium of 48 BC, the Battle of Pharsalus in 48 BC, the Battle of Zela of 47 BC and the Battle of Thapsus in 46 BC in Caesar's African campaign. A legion that fits the same sequence of locations is the Legio VI Ferrata, of which ballista would be an auxiliary unit. Known for his writings, Vitruvius was himself an architect. In Roman times architecture was a broader subject than at present including the modern fields of architecture, construction management, construction engineering, chemical engineering, civil engineering, materials engineering, mechanical engineering, military engineering and urban planning.
Frontinus mentions him in connection with the standard sizes of pipes. He is credited as father of architectural acoustics for describing the technique of echeas placement in theaters; the only building, that we know Vitruvius to have worked on is one he tells us about, a basi
Tuff known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa" when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous. Tuff is a soft rock, so it has been used for construction since ancient times. Since it is common in Italy, the Romans used it for construction; the Rapa Nui people used it to make most of the moai statues in Easter Island. Tuff can be classified as either sedimentary or igneous rock, they are studied in the context of igneous petrology, although they are sometimes described using sedimentological terms. The material, expelled in a volcanic eruption can be classified into three types: Volcanic gases, a mixture made of steam, carbon dioxide, a sulfur compound Lava, the name of magma when it emerges and flows over the surface Tephra, chunks of solid material of all shapes and sizes ejected and thrown through the airTephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases.
Magma explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface. These violent explosions produce solid chunks of material that can fly from the volcano. Chunks smaller than 2 mm in diameter are called volcanic ash. Among the loose beds of ash that cover the slopes of many volcanoes, three classes of materials are represented. In addition to true ashes of the kind described above, lumps of the old lavas and tuffs form the walls of the crater, which have been torn away by the violent outbursts of steam, pieces of sedimentary rocks from the deeper parts of the volcano that were dislodged by the rising lava and are intensely baked and recrystallized by the heat to which they have been subjected. In some great volcanic explosions, nothing but lumps of the old lavas and tuffs forming the walls of the crater etc. were emitted, as at Mount Bandai in Japan in 1888. Many eruptions have occurred in which the quantity of broken sedimentary rocks that mingled with the ash is great.
In the Scottish coalfields, some old volcanoes are plugged with masses consisting of sedimentary debris. These accessory or adventitious materials, however, as distinguished from the true ashes, tend to occur in angular fragments, when they form a large part of the mass, the rock is more properly a "volcanic breccia" than a tuff; the ashes vary in size from large blocks 20 ft or more in diameter to the minutest impalpable dust. The large masses are called "volcanic bombs". Many of them have ribbed or nodular surfaces, sometimes they have a crust intersected by many cracks like the surface of a loaf of bread. Any ash in which they are abundant is called an agglomerate. In those layers and beds of tuff that have been spread out over considerable tracts of land and which are most encountered among the sedimentary rocks, smaller fragments preponderate and bombs more than a few inches in diameter may be absent altogether. A tuff of recent origin is loose and incoherent, but the older tuffs have been, in most cases, cemented together by pressure and the action of infiltrating water, making rocks which, while not hard, are strong enough to be extensively used for building purposes.
If they have accumulated subaerially, like the ash beds found on Mt. Etna or Vesuvius at the present day, tuffs consist wholly of volcanic materials of different degrees of fineness with pieces of wood and vegetable matter, land shells, etc. but many volcanoes stand near the sea, the ashes cast out by them are mingled with the sediments that are gathering at the bottom of the waters. In this way, ashy muds, sands, or in some cases ashy limestones are being formed. Most of the tuffs found in the older formations contain admixtures of clay and sometimes fossil shells, which prove that they were beds spread out under water. During some volcanic eruptions, a layer of ashes several feet in thickness is deposited over a considerable area, but such beds thin out as the distance from the crater increases, ash deposits covering many square miles are very thin; the showers of ashes follow one another after longer or shorter intervals, hence thick masses of tuff, whether of subaerial or of marine origin, have a stratified character.
The coarsest materials or agglomerates show this least distinctly. Apart from adventitious material, such as fragments of the older rocks, pieces of trees, etc. the contents of an ash deposit may be described as consisting of more or less crystalline igneous rocks. If the lava within the crater has been at such a temperature that solidification has commenced, crystals are present, they may be of considerable size like the grey, rounded leucite crystals found on the sides of Vesuvius. Many of these are perfect and rich in faces because they grew in a medium, liquid and not viscous. Good crystals of augite and olivi
Stucco or render is a material made of aggregates, a binder, water. Stucco is applied wet and hardens to a dense solid, it is used as a decorative coating for walls and ceilings, as a sculptural and artistic material in architecture. Stucco may be used to cover less visually appealing construction materials, such as metal, cinder block, or clay brick and adobe. In English, "stucco" refers to a coating for the outside of a building and "plaster" to a coating for interiors. However, other European languages, notably including Italian, do not have the same distinction; this has led to English using "stucco" for interior decorative plasterwork in relief. The difference in nomenclature between stucco and mortar is based more on use than composition; until the latter part of the nineteenth century, it was common that plaster, used inside a building, stucco, used outside, would consist of the same primary materials: lime and sand. Animal or plant fibers were added for additional strength. In the latter nineteenth century, Portland cement was added with increasing frequency in an attempt to improve the durability of stucco.
At the same time, traditional lime plasters were being replaced by gypsum plaster. Traditional stucco is made of lime and water. Modern stucco is made of Portland cement and water. Lime is added to increase the workability of modern stucco. Sometimes additives such as acrylics and glass fibers are added to improve the structural properties of the stucco; this is done with what is considered a one-coat stucco system, as opposed to the traditional three-coat method. Lime stucco is a hard material that can be broken or chipped by hand without too much difficulty; the lime itself is white. Lime stucco has the property of being self-healing to a limited degree because of the slight water solubility of lime. Portland cement stucco is hard and brittle and can crack if the base on which it is applied is not stable, its color was gray, from the innate color of most Portland cement, but white Portland cement is used. Today's stucco manufacturers offer a wide range of colors that can be mixed integrally in the finish coat.
Other materials such as stone and glass chips are sometimes "dashed" onto the finish coat before drying, with the finished product known as "rock dash", "pebble dash", or as roughcast if the stones are incorporated directly into the stucco, used from the early 20th through the early 21st Century. As a building material, stucco is a durable and weather-resistant wall covering, it was traditionally used as both an interior and exterior finish applied in one or two thin layers directly over a solid masonry, brick, or stone surface. The finish coat contained an integral color and was textured for appearance. With the introduction and development of heavy timber and light wood-framed construction methods, stucco was adapted for this new use by adding a reinforcement lattice, or lath, attached to and spanning between the structural supports and by increasing the thickness and number of layers of the total system; the lath added support for the wet tensile strength to the brittle, cured stucco. The traditional application of stucco and lath occurs in three coats — the scratch coat, the brown coat and the finish coat.
The two base coats of plaster are either hand-applied or machine sprayed. The finish coat can be floated to a sand finish or sprayed; the lath material was strips of wood installed horizontally on the wall, with spaces between, that would support the wet plaster until it cured. This lath and plaster technique became used. In exterior wall applications, the lath is installed over a weather-resistant asphalt-impregnated felt or paper sheet that protects the framing from the moisture that can pass through the porous stucco. Following World War II, the introduction of metal wire mesh, or netting, replaced the use of wood lath. Galvanizing the wire made it corrosion resistant and suitable for exterior wall applications. At the beginning of the 21st century, this "traditional" method of wire mesh lath and three coats of exterior plaster is still used. In some parts of the United States, stucco is the predominant exterior for both residential and commercial construction. Stucco has been used as a sculptural and artistic material.
Stucco relief was used in the architectural decoration schemes of many ancient cultures. Examples of Egyptian and Etruscan stucco reliefs remain extant. In the art of Mesopotamia and ancient Persian art there was a widespread tradition of figurative and ornamental internal stucco reliefs, which continued into Islamic art, for example in Abbasid Samarra, now using geometrical and plant-based ornament; as the arabesque reached its full maturity, carved stucco remained a common medium for decoration and calligraphic inscriptions. Indian architecture used stucco as a material for sculpture in an architectural context, it is rare in the countryside. In Roman art of the late Republic and early Empire, stucco was used extensively for the decoration of vaults. Though marble was the preferred sculptural medium in most regards, stucco was better for use in vaults because it was lighter and better suited to adapt to the curvature of the ceiling