Ultramafic rocks (also referred to as ultrabasic rocks , although the terms are not wholly equivalent) are igneous and meta -igneous rocks with a very low silica content (less than 45%), generally >18% MgO , high FeO , low potassium , and are usually composed of greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks .
24-519: Hardin County is the name of six counties in the United States of America: Hardin County, Illinois Hardin County, Iowa Hardin County, Kentucky Hardin County, Ohio Hardin County, Tennessee Hardin County, Texas See also [ edit ] Harden County , New South Wales, Australia [REDACTED] Topics referred to by
48-415: A different process than typical ultramafic rocks. Metamorphism of ultramafic rocks in the presence of water and/or carbon dioxide results in two main classes of metamorphic ultramafic rock; talc carbonate and serpentinite . Talc carbonation reactions occur in ultramafic rocks at lower greenschist through to granulite facies metamorphism when the rock in question is subjected to metamorphism and
72-564: A greater percentage of calcic plagioclase. These grade into the anorthosites . Gabbro and norite often occur in the upper portions of the layered ultramafic sequences. Hornblendite and, rarely phlogopite , are also found. Volcanic ultramafic rocks are rare outside of the Archaean and are essentially restricted to the Neoproterozoic or earlier. Subvolcanic ultramafic rocks and dykes persist longer, but are also rare. There
96-573: A result, a distinctive type of vegetation develops on these soils. Examples are the ultramafic woodlands and barrens of the Appalachian mountains and piedmont , the "wet maquis " of the New Caledonia rain forests , and the ultramafic forests of Mount Kinabalu and other peaks in Sabah , Malaysia . Vegetation is typically stunted, and sometimes includes endemic species adapted to
120-503: Is different from Wikidata All article disambiguation pages All disambiguation pages Hardin County, Illinois Hardin County is a county located in the U.S. state of Illinois . According to the 2020 census , it has a population of 3,649, making it the least populous county in Illinois. Its county seat is Elizabethtown . Hardin County is located in the part of the state known as Little Egypt . Hardin County
144-413: Is evidence of ultramafic rocks elsewhere in the solar system. Examples include komatiite and picritic basalt . Komatiites can be host to ore deposits of nickel . Ultramafic tuff is extremely rare. It has a characteristic abundance of olivine or serpentine and a scarcity or absence of feldspar and quartz . Rare occurrences may include unusual surface deposits of maars of kimberlites in
168-509: Is underlain by ultramafic igneous rocks and igneous diatremes or breccia pipes . Most geologists accept the theory that the older rocks at the center of the uplift are a result of this deep-seated igneous activity. This activity may also have provided the fluorine in the fluorspar deposits in the region. Fluorspar , or calcium fluoride , was mined in Hardin County until the early 1990s. In recent years, average temperatures in
192-525: The 2010 census , there were 4,320 people, 1,915 households, and 1,234 families residing in the county. The population density was 24.3 inhabitants per square mile (9.4/km ). There were 2,488 housing units at an average density of 14.0 per square mile (5.4/km ). The racial makeup of the county was 97.3% white, 0.6% American Indian, 0.5% Asian, 0.3% black or African American, 0.1% Pacific islander, 0.3% from other races, and 0.8% from two or more races. Those of Hispanic or Latino origin made up 1.3% of
216-665: The Phanerozoic are rarer, and there are very few recognised true ultramafic lavas in the Phanerozoic. Many surface exposures of ultramafic rocks occur in ophiolite complexes where deep mantle-derived rocks have been obducted onto continental crust along and above subduction zones. Serpentine soil is a magnesium rich, calcium, potassium and phosphorus poor soil that develops on the regolith derived from ultramafic rocks. Ultramafic rocks also contain elevated amounts of chromium and nickel which may be toxic to plants. As
240-431: The U.S. Census Bureau , the county has a total area of 182 square miles (470 km ), of which 178 square miles (460 km ) is land and 4.1 square miles (11 km ) (2.2%) is water. It is the second-smallest county in Illinois by area. Hicks Dome ( 37°31′53″N 88°22′06″W / 37.53139°N 88.36833°W / 37.53139; -88.36833 ) is a geological feature in Hardin County. The Hicks Dome
264-425: The diamond fields of southern Africa and other regions. Technically ultrapotassic rocks and melilitic rocks are considered a separate group, based on melting model criteria, but there are ultrapotassic and highly silica-under-saturated rocks with >18% MgO which can be considered "ultramafic". Ultrapotassic, ultramafic igneous rocks such as lamprophyre , lamproite and kimberlite are known to have reached
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#1732773199796288-561: The 1912 election when the Republican Party was mortally divided. Hardin County would next be carried by a Democratic presidential candidate in Franklin D. Roosevelt ’s 1932 landslide victory, and not after that until Lyndon Johnson in 1964. The county did trend Democratic in the following three decades, actually voting more Democratic than the nation at-large between 1972 and 1996. Nonetheless, since 2000 Hardin County has followed
312-555: The American Revolutionary War and the Northwest Indian War. Hardin was murdered by Shawnee Indians while he was on a peace mission in 1792 for President George Washington , in what is now Shelby County , Ohio . In the 1790s and early 1800s, the Hardin County area, especially Cave-In-Rock , was notorious as a stronghold used by outlaws, bandits, river pirates, and counterfeiters. According to
336-681: The county seat of Elizabethtown have ranged from a low of 21 °F (−6 °C) in January to a high of 87 °F (31 °C) in July, although a record low of −22 °F (−30 °C) was recorded in January 1994 and a record high of 104 °F (40 °C) was recorded in August 2007. Average monthly precipitation ranged from 3.22 inches (82 mm) in October to 5.02 inches (128 mm) in May. As of
360-414: The metamorphic fluid has more than 10% molar proportion of CO 2 ( carbon dioxide ). When such metamorphic fluids have less than 10% molar proportion of CO 2 , reactions favor serpentinisation, resulting in chlorite - serpentine - amphibole type assemblages. The majority of ultramafic rocks are exposed in orogenic belts, and predominate in Archaean and Proterozoic terranes. Ultramafic magmas in
384-425: The population. In terms of ancestry, 26.5% were Irish , 23.8% were German , 10.4% were English , and 4.3% were American . Of the 1,915 households, 26.0% had children under the age of 18 living with them, 50.9% were married couples living together, 9.2% had a female householder with no husband present, 35.6% were non-families, and 31.7% of all households were made up of individuals. The average household size
408-470: The proportion of the worst-performing Democrat from before 2010. Ultramafic rock Intrusive ultramafic rocks are often found in large, layered ultramafic intrusions where differentiated rock types often occur in layers. Such cumulate rock types do not represent the chemistry of the magma from which they crystallized. The ultramafic intrusives include the dunites , peridotites and pyroxenites . Other rare varieties include troctolite which has
432-573: The same political trajectory as Tennessee , Missouri , Kentucky , West Virginia and Appalachian regions of adjacent states, whereby the Democratic Party's liberal views on social issues have produced dramatic swings to the Republican Party amongst its almost entirely Southern white population. The past six Presidential elections have observed a swing totalling 79 percentage points to the GOP, with Hillary Clinton in 2016 receiving barely half
456-445: The same term This disambiguation page lists articles about distinct geographical locations with the same name. If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Hardin_County&oldid=972320104 " Category : United States county name disambiguation pages Hidden categories: Short description
480-417: The soils. Often thick, magnesite - calcrete caprock , laterite and duricrust forms over ultramafic rocks in tropical and subtropical environments. Particular floral assemblages associated with highly nickeliferous ultramafic rocks are indicative tools for mineral exploration . Weathered ultramafic rocks may form lateritic nickel ore deposits . Ultramafic lava may have been detected on Io ,
504-958: The surface of the Earth. Although no modern eruptions have been observed, analogues are preserved. Most of these rocks occur as dikes , diatremes , lopoliths or laccoliths , and very rarely, intrusions. Most kimberlite and lamproite occurrences occur as volcanic and subvolcanic diatremes and maars ; lavas are virtually unknown. Vents of Proterozoic lamproite ( Argyle diamond mine ), and Cenozoic lamproite ( Gaussberg , Antarctica ) are known, as are vents of Devonian lamprophyre ( Scotland ). Kimberlite pipes in Canada, Russia and South Africa have incompletely preserved tephra and agglomerate facies . These are generally diatreme events and as such are not lava flows although tephra and ash deposits are partially preserved. These represent low- volume volatile melts and attain their ultramafic chemistry via
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#1732773199796528-498: Was 2.25 and the average family size was 2.78. The median age was 46.3 years. The median income for a household in the county was $ 27,578 and the median income for a family was $ 38,576. Males had a median income of $ 42,955 versus $ 26,683 for females. The per capita income for the county was $ 18,515. About 17.4% of families and 22.3% of the population were below the poverty line , including 37.4% of those under age 18 and 14.6% of those age 65 or over. In its early history, Hardin County
552-555: Was named for Hardin County , Kentucky , which was named in honor of Colonel John Hardin , an officer in the American Revolutionary War and the Northwest Indian War . Hardin County was formed in 1839 from Pope County . Additional area was later added from Gallatin County . Hardin County was named for Hardin County , Kentucky , which was named in honor of Colonel John Hardin , an officer in
576-497: Was opposed to the “ Yankee ” Republican Party and its Civil War against the South – with whom it was closely allied both culturally and economically. It did not vote for a Republican presidential candidate until Theodore Roosevelt ’s 1904 landslide. Since 1904, however, Hardin County has turned powerfully Republican. Like the nearby counties of Johnson , Massac and Pope , it managed to remain loyal to William Howard Taft during
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