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Topic: Trachyte

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  Trachyte - LoveToKnow 1911
Trachytic rocks are typically porphyritic, and some of the bestknown examples, such as the trachyte of Drachenfels on the Rhine, show this character excellently, having large sanidine crystals of tabular form an inch or two in length scattered through their fine-grained groundmass.
In the neighbourhood of Rome, Naples and the island of Ischia trachytic lavas and tuffs are of common occurrence.
Closely allied to the trachytes are the Keratophyres, which occur mainly in Palaeozoic strata in the Harz (Germany), in the Southern Uplands of Scotland, in Cornwall, andc.
www.1911encyclopedia.org /Trachyte   (1467 words)

 Ascension Island Geology
Trachyte and rarer rhyolite flows and flow domes are predominantly found in the central and eastern parts of Ascension.
The trachyte forming the Crags has a K-Ar whole rock age of 740,000 years, and is mantled by mafic scoria derived from a vent to the southeast.
The trachyte and rhyolite flows and pumice are isotopically similar to the mafic flows, with the notable exception that trachyte and rhyolite with low Sr have very high initial Sr isotope ratios, the most likely source of the radiogenic Sr being through introduction of seawater.
ags.ou.edu /~bweaver/Ascension/ai-geol.htm   (1801 words)

 Trachyte   (Site not responding. Last check: 2007-10-16)
Glassy forms of Trachyte (obsidian) occur, as in Iceland, and pumiceous varieties are known (in Teneriffe and elsewhere), but these rocks as contrasted with the rhyolites have a remarkably strong tendency to crystallize, and are rarely to any considerable extent vitreous.
In the neighborhoord of Rome, Naples and the island of Ischia trachytic lavas and tuffs are of common occurrence.
Closely allied to the trachytes are the Keratophyres, which occur mainly in Palaeozoic strata in the Harz (Germany), in the Southern Uplands of Scotland, in Cornwall, etc. They are usually porphyritic and fluidal; and consist mainly of alkali feldspar (anorthoclase principally, but also albite and orthoclase), with a small quantity of chlorite and iron oxides.
trachyte.iqnaut.net   (1027 words)

 Commerce Group Corp. - About Us: Mining - San Sebastian Mine
The overall morphology of the trachyte is one of a large localized mound of trachyte sitting in depressions in the basalt.
Evidence of steep-seated structures that controlled the extrusion of the trachyte and the intrusion quartz monzonite dike is not apparent in the vicinity of the mine.
Silicification is primarily restricted to the trachyte, whereas, argillic alteration is pervasive throughout the trachyte and quartz monzonite.
www.commercegroupcorp.com /AboutUs/Mining/SanSeb.htm   (2369 words)

 TRACHYTE (Gr. rpaxus, ... - Online Information article about TRACHYTE (Gr. rpaxus, ...
Trachytic rocks are typically porphyritic, and some of the best-known examples, such as the trachyte of Drachenfels on the Rhine, show this character excellently, having large sanidine crystals of See also:
Two types of ground-mass are generally recognized: the trachytic, composed mainly of long, narrow, sub-parallel rods of sanidine, and the orthophyric, consisting of small, squarish or rectangular prisms of the same mineral.
island of Ischia trachytic lavas and tuffs are of common occurrence.
encyclopedia.jrank.org /TOO_TUM/TRACHYTE_Gr_rpaxus_rough_.html   (1912 words)

 Olympus Microscopy Resource Center: Polarized Light Microscopy Gallery - Trachyte Porphyry
First discovered in ancient Thrace, the name for trachyte is generally believed to have been derived from a Greek word meaning “rough” or “coarse.” Such etymology is quite fitting since trachyte typically occurs as porphyry, a rock in which large, conspicuous crystals are set in a fine-grained matrix.
Trachyte also often features a banded or striated appearance due to the flow of the lava from which it formed.
Trachyte was a very popular building material in ancient Rome, where it was also utilized for ornamental purposes and to pave roads.
www.olympusmicro.com /galleries/polarizedlight/pages/trachyteporphyrysmall.html   (225 words)

 Darwin - Ascension Island
The trachyte is generally of a pale brown colour, stained with small darker patches; it contains broken and bent crystals of glassy feldspar, grains of specular iron, and fl microscopical points, which latter, from being easily fused, and then becoming magnetic, I presume are hornblende.
Within the space,[10] mainly formed of trachyte, some basaltic streams have burst forth; and not far from the summit of Green Mountain, there is one stream of quite fl, vesicular basalt, containing minute crystals of glassy feldspar, which have a rounded appearance.
Scrope[41] has described a remarkable columnar trachyte in the Panza Islands, which seems to have been injected into an overlying mass of trachytic conglomerate: it is striped with zones, often of extreme tenuity, of different textures and colours; the harder and darker zones appearing to contain a larger proportion of silica.
www.bweaver.nom.sh /darwin/darwinai.htm   (8772 words)

 When Hualalai Turned Viscous
Trachyte, pronounced tra- (as in trash) kite, a very viscous type of lava, flows much slower than what we witness at Kilauea and forms a more exaggerated topography.
Trachyte is also characterized by magma that is relatively rich in sodium and potassium, which are very large elements that do not flow easily and add to the lava's viscosity.
Many trachyte exposures also occur in the West Maui mountains and on the East Moloka`i shield, perhaps formed when those mountains made the transition from the shield to the post-shield stage.
hvo.wr.usgs.gov /volcanowatch/2004/04_08_12.html   (909 words)

 Jeju Island Nature Environment Ecology Information System   (Site not responding. Last check: 2007-10-16)
Geographical features of Jeju Island consists of the Seoguipo layer, formed at the early 4th period of the Cenozoic era, and sedimentary rock, basalt, trachyte, and andersite at the Sungsan, Sinyangri layer formed at the late 4th period of the Cenozoic era, and volcanic puzzolana, erupted from the parasite volcanoes.
Trachyte rocks, made of fish fossils, typically represented by Sanbangsan trachyte, are detected on coastal areas at the south, connecting Sanbangsan and Yeochongmang.
The characteristics of the Seoguipo andesite of trachyte, covering Seoguipo layer at cliffs of Seoguipo stratum basset, and andesite of trachyte, distributed at Jungmun areas, are presumed to be types of lava rocks that are 0.55 million to 0.31 million years old.
www.jejunature.com /emain/nature/e_contents_nat21.html   (747 words)

 Volcanic and Geologic Terms
Trachyandesite: An extrusive rock intermediate in composition between trachyte and andesite.
Trachybasalt: An extrusive rock intermediate in composition between trachyte and basalt.
Trachyte: A group of fine-grained, generally porphyritic, extrusive igneous rocks having alkali feldspar and minor mafic minerals as the main components, and possibly a small amount of sodic plagioclase.
volcano.und.nodak.edu /vwdocs/glossary.html   (4560 words)

 * Trachyte - (Jewelry): Definition
Trachyte: A light gray igneous rock with a rough surface consisting of orthoclase feldspar.
Composed predominantly of basalt, several other volcanic rocks including trachyte and rhyolite are not uncommon.
A glassy kind of orthoclase, called sanidine, is typical of felsic volcanic rocks and is found in the trachytes of the Drachenfels, Germany.
en.mimi.hu /jewelry/trachyte.html   (190 words)

The complex consists of trachyte and pantellerite lava and ash-flow tuffs.
Mineral phases from the trachyte and the youngest pantellerite have been analyzed by electron microprobe.
The younger trachyte ferromagnesian assemblage is fayalite + ferrohedenbergite + ilmenite + aenigmatite.
gsa.confex.com /gsa/2004AM/finalprogram/abstract_78951.htm   (461 words)

 New Page 1
Trachyte is a sodium and potassium-rich rock that is mafic poor.
Trachyte is an alkali rich rock that has more sodium and potassium than most of the basalt on Big Island.
Because trachyte has excess alkali minerals the silica content is reduced, causing this type of lava to flow faster than a rhyolitic flow but slower than a basaltic flow.
www.albion.edu /geology/Geo210_hawaii/Kohala/trachyte.htm   (426 words)

 Hot spot magmatic processes
Both Sr and O isotopic ratios are higher in the trachytes than in Hualalai alkalic lavas, which is best explained by reaction with, or assimilation of, altered Hualalai shield basalts at shallow depth.
Major, trace element, and isotopic variations between trachytes are consistent with their evolution by fractional crystallization from a Puu Anahulu parent.
Subtle rare earth element and radiogenic isotopic distinctions between trachytes from the three locations on Hualalai indicate that the roof of the shallow magma reservoir may have been irregular, trapping magma and allowing some trachytes to evolve independently from others.
www.mbari.org /volcanism/Hawaii/HR-MagmProc.htm   (1608 words)

is ideal for this, as it has produced a wide range of rock types from basalts to trachytes and comendites, and is located on young oceanic lithosphere near the mid Atlantic Ridge and far from continental influences.
View from the trachyte dome of White Horse to Letterbox.
Cinder cones of The Sisters in the central part of the island, with pale trachyte of Daly's Crags showing through the mantling of cinders.
www.dur.ac.uk /j.p.davidson/ascension.html   (209 words)

 Geoscience - The Earth - Australian Landforms - Glass House Mountains
These are the eroded cores of central volcanoes of Cenozoic age, formed 25 to 27 million years ago, which rise abruptly from the coastal region about 60 kms north of Brisbane, Queensland.
Mt. Beerwah, made of trachyte, is the highest peak at 556 m.
Beerburrum (276 m) and Mt. Miketeebumulgrai form dome-like intrusions of trachyte, and Mt. Coonowrin is a steep spire of rhyolite.
www.amonline.net.au /geoscience/earth/glass_house.htm   (193 words)

 [No title]
There traces of volcanic rocks (Trachyte) within some of the craters, and all craters are associated with dykes formed by two parallel uptilted rows of sandstone, filled with white trachyte in-between.
On the south side the crater has a double rim, and the relatively flat area, offering full command of the surrounding plain, shows evidence of prehistoric dwellings and is littered with late paleolithic tools flaked from the fused sandstone of the crater rim.
Lying farther off the main group (in the distance, beyond crater C on photo), crater D is fully capped by gray trachyte, while crater F is a small perfectly round ring with an empty crater.
www.fjexpeditions.com /desert/geography/craters/craters.htm   (896 words)

 Geoscience - The Earth - Australian Landforms - The Warrumbungles
Large volumes of trachytic pyroclastics were erupted (now tuff and breccia) as a blanket over the surrounding countryside, together with formation of lava domes and short, thick trachyte flows.
Over time, the erupted magma continued to be less viscous, and trachyte eruptions were replaced by basaltic flows (hawaiite and mugearite) which became thinner and longer, until all activity ceased around 13 million years ago.
One famous feature is the Breadknife, a dyke which forms a narrow trachyte wall intruding pyroclastics and rising steeply into the air.
www.amonline.net.au /geoscience/earth/warrumbungles.htm   (345 words)

These lavas are no longer exposed on the subaerial surface but have been dredged from submarine portions of the northwest rift zone.
Presently, the volcano is mantled by alkalic lavas erupted during the post-shield stage of volcanism (mostly alkali olivine basalts but rare occurrences of Trachyte are also present).
Also shown (in brown) are the 100000 year old trachytes of Puu Waawaa), the 1859 lava flow from nearby Mauna Loa (in grey), and the Kahaluu water shaft (marked by an X""), where Hualalai generated tholeiitic basalts are found only 75 feet below the surface.
www.soest.hawaii.edu /GG/HCV/hualalai.html   (961 words)

 Igneous Rocks & Plate Tectonics
This causes an Fe-depletion trend causing magmas to evolve to mugearites, benmoreites or trachytes, and eventually rhyolites and/or peralkaline rhyolites.
Quaternary volcanoes along the axis of the central rift zones, in Kenya and Tanzania consist of phonolite, trachyte, or peralkaline rhyolite.
In nearly all cases, peralkaline rhyolites are associated with mildly alkaline silica-saturated basalts, hawaiites, mugearites, and trachytes.
www.tulane.edu /~sanelson/eens211/igneous_rocks_plate_tectonics.htm   (8714 words)

 ROCK LANDFORMS of Australia & NZ - IGNEOUS LANDFORMS - Case Study (A)
The main volcanic rock is trachyte, which occurs in a variety of forms, including spectacular domes, plugs and dykes.
Trachytic magma, being viscous, is often associated with explosive eruptions which deposit breccia, tuff and pumice over their surrounds.
During formation the lava dome swelled and shed blocks of trachyte breccia from its outer cooling and expanding surface.
www.vnc.qld.edu.au /enviro/landform/landf-ic.htm   (647 words)

 Trachyte Knob - A Mountain Landmark In Southern Teller County, Colorado
Trachyte Knob - A Mountain Landmark In Southern Teller County, Colorado
Okay, okay, it might not be the most exciting picture, but this is Trachyte Knob located in southern Teller County in the region frequently referred to as Gillette.
At the junction of State Highway 67 and Teller County Road 81, Trachyte Knob can be seen to the southeast.
www.tellercounty.net /trachyte-knob.htm   (131 words)

 Geokem - Rhyolites-Trachytes
Perhaps surprisingly, trachytes and phonolites are very similar to rhyolites except that there is no Nb-Ta negative anomaly present.
Pantellerites are an unusual form of trachyte named after the island of Pantellaria between Sicily and Africa (near Carthage).
Trachytes are usually sodic but potassic varieties may be found on potassic OIB islands such as Gough or Tristan da Cunha in the south Atlantic.
www.geokem.com /rhyolites-trachytes.html   (1944 words)

Tsaratanana, the highest peak in north-central Madagascar (~2876 m), is one of several Cenozoic eruptive centers that extend from the Seychelles south to the Comores Islands.
Miocene volcanism (~10 Ma) is of peraluminous type and consists of less abundant basanitic flows and more abundant phonolitic and trachytic tuffs and flows.
The Sr- and O-isotope variations observed in trachytes and phonolites point to contamination of the magmas by only small amount of crustal materials (<5%).
gsa.confex.com /gsa/2003AM/finalprogram/abstract_65599.htm   (364 words)

 Trachyte   (Site not responding. Last check: 2007-10-16)
One of the many people that can be encountered working at the Guild Library in the city, Trachyte is the most likely to respond to requests for information.
While not actually liking the interference to his work, Trachyte does enjoy annoying people of a lower intelligence than his own (rated in the region of 149 IQ), thus he takes great delight in talking with adventurers, most of which have no real idea of what they are after in the first place.
It is thought that Trachyte has a home elsewhere in the city, but as to its location no one is certain, for most of the time he will be encountered within the library, or his research quarters on the second floor.
www.guernsey.net /~xott/trachyte.html   (203 words)

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