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Spherulites
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 extrusive rock, 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 rhyolite, rhyolitic lava flows known as obsidian flows. These flows have a high content of silicon dioxide, silica, granting them a high viscosity. The high viscosity inhibits atomic diffusion, 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, Brittleness, brittle, and amorphous; it therefore Fracture (mineralogy)#Conchoidal fracture, fractures with sharp edges. In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Recrystallization (geology)
In geology, solid-state recrystallization is a metamorphic process that occurs under high temperatures and pressures where atoms of minerals are reorganized by diffusion and/or dislocation glide. During this process, the physical structure of the minerals is altered while the composition remains unchanged. This is in contrast to metasomatism, which is the chemical alteration of a rock by hydrothermal and other fluids. Solid-state recrystallization can be illustrated by observing how snow recrystallizes to ice. When snow is subjected to varying temperatures and pressures, individual snowflakes undergo a physical transformation but their composition remains the same. Limestone is a sedimentary rock that undergoes metamorphic recrystallization to form marble, and clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of w ... [...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 various c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tuff
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 lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, ''tuffaceous sandstone''). Tuff composed of sandy volcanic material can be referred to as volcanic sandstone. Tuff is a relatively soft rock, so it has been used for construction since ancient times. Because it is common in Italy, the Romans used it often for construction. The Rapa Nui people used it to make most of the ''moai'' statues on Easter Island. Tuff can be classified as either igneous or sedimentary rock. It is usually studied in the context of igneous petrology, although it is sometimes described using sedimentological terms. Tuff is often erroneously called tufa in guidebooks and in television programmes. Volcanic ash The material that is expelled in a volcanic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ameca, Jalisco
Ameca ( nah, Amecatl "string of water") is a city and municipality, in Jalisco in central-western Mexico. The municipality covers an area of 685.73 km². The city is bisected by the Ameca River which drains to the Pacific Ocean near Puerto Vallarta. It is also approximately 83 km (approximately 50 miles) from the state capital and one of Mexico's largest commercial centers, Guadalajara. The city is also the seat and largest city of the federal sub-division Región Valles, which compromises the municipalities situated on the central valleys of Jalisco. As of 2010, the municipality had a total population of 57,340, and the city had a population of 36,156, making it the 15th largest city of Jalisco in terms of population. History In the early 16th century Ameca was the center of the small kingdom of Ameca. This state was conquered by the Spanish in 1524. It was part of the alcaldia mayor of Autlan, New Spain during the Spanish colonial period. The first of the con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ahualulco De Mercado
Ahualulco de Mercado is a City and municipality, in Jalisco in central-western Mexico. The municipality covers an area of 134.22 km2. As of 2005, the municipality had a total population of 21,465. Name origin Ahualulco comes from the Nahuatl word ''Ayahualolco'' which means "place of water crowned" or "place around the water." Geographical description Location Ahualulco de Mercado is located in central Jalisco, at coordinates 20° 37'20" to 20° 46'10" north latitude and 103° 52'00" to 104º 04'30" west longitude. The municipality is bordered on the north by the municipalities of Etzatlán, San Juanito de Escobedo and Tequila, on the east by the town of Teuchitlán, on the south by the municipalities Teuchitlán and Ameca, and on the west by the municipalities of Ameca and Etzatlán. It lies on the road from El Refugio to San Marcos and is the most populous town and tourism in this area. Weather The weather is semi-arid with dry winter and spring, and semi-warm ... [...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, United States ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arizona
Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is 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 Mexican states of Sonora and Baja California to the south and southwest. Arizona is the 48th state and last of the 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 the Mexican–American War, Mexico ceded much of this territory to the United States in 1848. The southernmost portion of the state was acquired in 1853 through the Gadsden Purchase. Southern Arizona is known for its desert cl ... [...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 Big I ... [...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 New ... [...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 smaller islands. It is the 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 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. In 1840, representatives of the United Kingdom and Māori chiefs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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