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Spherulite
In petrology, spherulites () are small, rounded bodies that commonly occur in vitreous igneous rocks. They are often visible in specimens of obsidian, pitchstone, and rhyolite as globules about the size of millet seed or rice grain, with a duller luster than the surrounding glassy base of the rock, and when they are examined with a lens they prove to have a radiate fibrous structure. Structure Under the microscope the spherulites are of circular outline and are composed of thin divergent fibers that are crystalline as verified with polarized light. Between crossed Nicols, a black cross appears in the spherulite; its axes are usually perpendicular to one another and parallel to the crosshairs; as the microscope stage is rotated the cross remains steady; between the black arms there are four bright sectors. This shows that the spherulite consists of radiate, doubly refracting fibers that have a straight extinction; the arms of the black cross correspond to those fibers that ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Obsidian
Obsidian () is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, granting them a high viscosity. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step (nucleation) in the formation of mineral crystals. Together with rapid cooling, this results in a natural glass forming from the lava. Obsidian is hard, brittle, and amorphous; it therefore fractures with sharp edges. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades. Origin and properties The '' Natural History'' by the Roman writer Pliny the E ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained ( aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite. Rhyolitic magma is extremely viscous, due to its high silica content. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been extensively used for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil amendment. Description R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhyolite Pmg Ss 2006
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent to granite. Rhyolitic magma is extremely viscous, due to its high silica content. This favors explosive eruptions over effusive eruptions, so this type of magma is more often erupted as pyroclastic rock than as lava flows. Rhyolitic ash-flow tuffs are among the most voluminous of continental igneous rock formations. Rhyolitic tuff has been extensively used for construction. Obsidian, which is rhyolitic volcanic glass, has been used for tools from prehistoric times to the present day because it can be shaped to an extremely sharp edge. Rhyolitic pumice finds use as an abrasive, in concrete, and as a soil amendment. Description Rhyolite is an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithophysa
A lithophysa (plural lithophysae, from Greek ''lithos'' "stone" + ''physan'' "to blow") is a felsic volcanic rock with a spherulitic structure and interior cavity with concentric chambers. Its outer shape is spherical or lenticular. They vary in size from very small up to twelve feet in diameter depending on the age of the magma chamber. These rocks are usually found within obsidian or rhyolite lava flows. Lavas low in feldspar minerals may produce a version known as snowflake obsidian. These cavities are believed to be caused by expanding gases in tuffs and rhyolitic lavas before solidification. If the cavity becomes lined with crystals it may be referred to as a geode or if filled partially or fully with agate, jasper or opal it is called a thunderegg. The term vug is also used for similar cavities although the meaning of vug is usually restricted to cavities in rocks formed by the removal of material such as soluble minerals. These cavities usually contain layers of vario ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steens Mountain
Steens Mountain is in the southeastern part of the U.S. state of Oregon, and is a large fault-block mountain. Located in Harney County, it stretches some north to south, and rises from the west side the Alvord Desert at elevation of about to a summit elevation of . Steens Mountain is not part of a mountain range but is properly a single mountain, the largest of Oregon's fault-block mountains.Conkling, C., Jackman, E. R., & Scharff, J. (1967)Steens Mountain in Oregon's high desert country Caxton Press. Retrieved April 25, 2022 The Steens Mountain Wilderness encompasses of Steens Mountain. of the Wilderness are protected from grazing and free of cattle. History The mountain was called the "Snowy Mountains" by John Work, one of the fur traders who were the first Europeans in the area. It was renamed in 1860 for United States Army Major Enoch Steen, who fought and drove members of the Paiute tribe off the mountain. American Indians used the Steens Mountain, particularly ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspars and the ''alkali'' (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight. Feldspars crystalize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. Compositions The feldspar group of minerals consists of tectosilicates, silicate minerals in which silicon ions are linked by shared oxygen ions to form a three-dimensional network. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: * potassium feldspar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polygon
In geometry, a polygon () is a plane figure that is described by a finite number of straight line segments connected to form a closed '' polygonal chain'' (or ''polygonal circuit''). The bounded plane region, the bounding circuit, or the two together, may be called a polygon. The segments of a polygonal circuit are called its ''edges'' or ''sides''. The points where two edges meet are the polygon's '' vertices'' (singular: vertex) or ''corners''. The interior of a solid polygon is sometimes called its ''body''. An ''n''-gon is a polygon with ''n'' sides; for example, a triangle is a 3-gon. A simple polygon is one which does not intersect itself. Mathematicians are often concerned only with the bounding polygonal chains of simple polygons and they often define a polygon accordingly. A polygonal boundary may be allowed to cross over itself, creating star polygons and other self-intersecting polygons. A polygon is a 2-dimensional example of the more general polytope in any nu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the List of island countries, sixth-largest island country by area, covering . New Zealand is about east of Australia across the Tasman Sea and south of the islands of New Caledonia, Fiji, and Tonga. The country's varied topography and sharp mountain peaks, including the Southern Alps, owe much to tectonic uplift and volcanic eruptions. New Zealand's Capital of New Zealand, capital city is Wellington, and its most populous city is Auckland. The islands of New Zealand were the last large habitable land to be settled by humans. Between about 1280 and 1350, Polynesians began to settle in the islands and then developed a distinctive Māori culture. In 1642, the Dutch explorer Abel Tasman became the first European to sight and record New Zealand. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silver Cliff, Colorado
The Town of Silver Cliff is the Statutory Town that is the most populous municipality in Custer County, Colorado, United States. The population was 587 at the 2010 census, up from 512 in 2000. History Silver Cliff was formed in the late 1870s to house the miners of its namesake, the Silver Cliff mine, and other silver mines in the neighborhood, such as the Bull-Domingo. The town, incorporated in 1879, had 5,040 residents by the 1880 census, making it the third most populous town in Colorado, after Denver and Leadville. Silver Cliff was the county seat from 1886 (when the town won the seat from Rosita) to 1928 (when the seat moved to nearby Westcliffe). The Silver Cliff mine, also known as the Geyser mine, is on the hill immediately north of the town. Although a large operation that employed many residents of Silver Cliff, the mine was the unfortunate object of eastern stock manipulators. Shares in the Silver Cliff mine were promoted in 1879 by James R. Keene, a famous N ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a U.S. state, state in the Southwestern United States. It is the list of U.S. states and territories by area, 6th largest and the list of U.S. states and territories by population, 14th most populous of the 50 states. Its capital city, capital and List of largest cities, largest city is Phoenix, Arizona, Phoenix. Arizona is part of the Four Corners region with Utah to the north, Colorado to the northeast, and New Mexico to the east; its other neighboring states are Nevada to the northwest, California to the west and the List of states of Mexico, Mexican states of Sonora and Baja California (state), Baja California to the south and southwest. Arizona is the 48th state and last of the contiguous United States, contiguous states to be admitted to the Union, achieving statehood on February 14, 1912. Historically part of the territory of in New Spain, it became part of independent Mexico in 1821. After being defeated in th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sierra De Ameca
Sierra (Spanish for "mountain range" and " saw", from Latin ''serra'') may refer to the following: Places Mountains and mountain ranges * Sierra de Juárez, a mountain range in Baja California, Mexico * Sierra de las Nieves, a mountain range in Andalusia, Spain * Sierra Madre (other), various mountain ranges ** Sierra Madre (Philippines), a mountain range in the east of Luzon, Philippines * Sierra mountains (other) * Sierra Nevada, a mountain range in the U.S. states of California and Nevada * Sierra Nevada (Spain), a mountain range in Andalusia, Spain * Sierra de San Pedro Mártir, a mountain range in Baja California, Mexico * Sierra Maestra, a mountain range in Cuba Other places Africa * Sierra Leone, a country located on the coast of West Africa Asia * Sierra Bullones, Bohol, Philippines Europe * Sierra Nevada National Park (Spain), Andalusia, Spain * Sierra Nevada Observatory, Granada, Spain North America * High Sierra Trail, California, Unite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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