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Shatter Cones
Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the range of . Morphology Shatter cones have a distinctively conical shape that radiates from the top (''apex'') of the cones repeating cone-on-cone in large and small scales in the same sample. Sometimes they have more of a spoon shape on the side of a larger cone. In finer-grained rocks such as limestone, they form an easily recognizable "horsetail" pattern with thin grooves (''striae''). However, the word "striae" should not be used to describe shatter cones, as that is considered misleading. Coarser grained rocks tend to yield less well developed shatter cones, which may be difficult to distinguish from other geological formations such as slickensides. Geologists have various theories of what causes shatter cones to form, including compre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stria
Stretch marks, also known as striae () or striae distensae, are a form of scarring on the skin with an off-color hue. Over time they may diminish, but will not disappear completely. Striae are caused by tearing of the dermis during periods of rapid growth of the body, such as during puberty or pregnancy, in which they usually form during the last trimester. Usually on the stomach, these striae also commonly occur on the breasts, thighs, hips, lower back, and buttocks. Pregnancy-related striae are known as ''striae gravidarum''. Striae may also be influenced by the hormonal changes associated with puberty, pregnancy, bodybuilding, or hormone replacement therapy. There is no evidence that creams used during pregnancy prevent stretch marks. Once they have formed there is no clearly effective treatment, though various methods have been attempted and studied. Signs and symptoms Striae, or "stretch marks", begin as reddish or purple lesions, which can appear anywhere on the body, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Impact Craters
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Lunar impact craters range from microscopic craters on lunar rocks returned by the Apollo Program and small, simple, bowl-shaped depressions in the lunar regolith to large, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth. Impact craters are the dominant geographic features on many solid Solar System objects including the Moon, Mercury, Callisto, Ganymede and most small moons and asteroids. On other planets and moons that experience more active surface geological processes, such as Earth, Venus, Europa, Io and Titan, visible impact craters are less common because they become erod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stishovite
Stishovite is an extremely hard, dense tetragonal form ( polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle. Stishovite was named after Sergey M. Stishov, a Russian high-pressure physicist who first synthesized the mineral in 1961. It was discovered in Meteor Crater in 1962 by Edward C. T. Chao. Unlike other silica polymorphs, the crystal structure of stishovite resembles that of rutile (TiO2). The silicon in stishovite adopts an octahedral coordination geometry, being bound to six oxides. Similarly, the oxides are three-connected, unlike low-pressure forms of SiO2. In most silicates, silicon is tetrahedral, being bound to four oxides. It was long considered the hardest known oxide (~30 GPa Vickers); however, boron suboxide has been discovered in 2002 to be much harder. At normal temperature and pressure, stishovite is metastable. Stishovite can be se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shocked Quartz
Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These planes, which show up as lines under a microscope, are called planar deformation features (PDFs), or shock lamellae. Discovery Shocked quartz was discovered following underground nuclear weapons testing, which generated the intense pressures required to alter the quartz lattice. Eugene Shoemaker showed that shocked quartz is also found inside craters created by meteor impact, such as the Barringer Crater and Chicxulub crater. The presence of shocked quartz supports that such craters were formed by impact, because a volcanic eruption would not generate the required pressure. Lightning is now known to contribute to the surface record of shocked quartz grains, complicating identification of hypervelocity impact features. Formation Shocke ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lechatelierite
Lechatelierite is silica glass, amorphous SiO2, non-crystalline mineraloid. Structure Lechatelierite is a mineraloid as it does not have a crystal structure. Although not a true mineral, it is often classified in the quartz mineral group. Formation One common way in which lechatelierite forms naturally is by very high temperature melting of quartz sand during a lightning strike. The result is an irregular, branching, often foamy hollow tube of silica glass called a fulgurite. Not all fulgurites are lechatelierite; the original sand must be nearly pure silica. Lechatelierite also forms as the result of high pressure shock metamorphism during meteorite impact cratering and is a common component of a type of glassy ejecta called tektites. Most tektites are blobs of impure glassy material, but tektites from the Sahara Desert in Libya and Egypt, known as '' Libyan desert glass'', are composed of almost pure silica that is almost pure lechatelierite. High pressure experiments have s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coesite
Coesite is a form ( polymorph) of silicon dioxide Si O2 that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first synthesized by Loring Coes Jr., a chemist at the Norton Company, in 1953.The word "coesite" is pronounced as "Coze-ite" after chemist Loring Coes Jr. Occurrences In 1960, a natural occurrence of coesite was reported by Edward C. T. Chao, in collaboration with Eugene Shoemaker, from Barringer Crater, in Arizona, US, which was evidence that the crater must have been formed by an impact. After this report, the presence of coesite in unmetamorphosed rocks was taken as evidence of a meteorite impact event or of an atomic bomb explosion. It was not expected that coesite would survive in high pressure metamorphic rocks. In metamorphic rocks, coesite was initially described in eclogite xenoliths from the mantle of the Earth that were carried up by ascending magmas; kimberlite is the most c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Breccia
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of different origins, as indicated by the named types including sedimentary breccia, tectonic breccia, igneous breccia, impact breccia, and hydrothermal breccia. A megabreccia is a breccia composed of very large rock fragments, sometimes kilometers across, which can be formed by landslides, impact events, or caldera collapse. Types Breccia is composed of coarse rock fragments held together by cement or a fine-grained matrix. Like conglomerate, breccia contains at least 30 percent of gravel-sized particles (particles over 2mm in size), but it is distinguished from conglomerate because the rock fragments have sharp edges that have not been worn down. These indicate that the gravel was deposited very close to its source area, since other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slate Islands (Ontario)
The Slate Islands are a small archipelago in Lake Superior, Ontario, Canada, about south of the town of Terrace Bay. The island group, consisting of 15 islands in total, was created by a meteorite impact which formed a crater about wide. In 1985, the Ontario government established the Slate Islands as a natural environment provincial park. The islands are notable for having Ontario's largest herd of boreal woodland caribou. Geography The island group consists of two main islands (Patterson and Mortimer), five minor islands (McColl, Edmonds, Bowes, Delaute and Dupuis islands) and numerous islets. The total surface area is about . The nearby Leadman Group of islands, about east, is often considered part of the Slate Islands. This group includes Leadman, Cape, Spar and Fish Islands. Human history Human sites have been found on the islands dating to about 1000CE. A lighthouse was built on Patterson Island, the largest island, in 1903 to help ships locate the harbour at the ne ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slickensides
In geology, a slickenside is a smoothly polished surface caused by frictional movement between rocks along a fault. This surface is typically striated with linear features, called slickenlines, in the direction of movement. Geometry of slickensides A slickenside can occur as a single surface at a fault between two hard surfaces. Alternatively, the gouge between the fault surfaces may contain many anastamosing slip surfaces that host slickensides. These slip surfaces are on the order of 100 micrometers thick, and the size of the grains that constitute the surface are ultra-fine (0.01-1 micrometers in diameter).Power, William L., and Terry E. Tullis. "The relationship between slickenside surfaces in fine-grained quartz and the seismic cycle." Journal of Structural Geology 11.7 (1989): 879-893. These grains are unlike typical grains of fault rock in that they have irregular grain boundaries and few crystal lattice defects (termed dislocations). Slickensides have conspicuo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite, a closely related rock, which contains a high percentage of the mineral dolomite, . ''Magnesian limestone'' is an obsolete and poorly-defined term used variously for dolomite, for limes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slate Islands Shattercone
Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. The foliation in slate is called " slaty cleavage". It is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression. When expertly "cut" by striking parallel to the foliation, with a specialized tool in the quarry, many slates will display a property called fissility, forming smooth flat sheets of stone which have long been used for roofing, floor tiles, and other purposes. Slate is frequently grey in color, especially when seen, en masse, covering roofs. However, slate occurs in a variety of colors even from a single locality; for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
