NationMaster - Encyclopedia: Trachyte

Trachyte is an igneous, volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present. (See the QAPF diagram). Biotite, clinopyroxene and olivine are common accessory minerals. Image File history File links Mineraly. ... Image File history File links Mineraly. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Ignimbrite is a deposit of a pyroclastic flow. ... An aphanite is an igneous rock with a fine-grained structure. ... (For other meanings of Porphyr, see Porphyry) The baptismal font in the Cathedral of Magdeburg is made of rose porphyry from a site near Assuan, Egypt Porphyry is a very hard red, green or purple igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ... Quartz is one of the most common minerals in the Earths continental crust. ... The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. ... A big crystal of Nepheline from CanaÃ£ Massif, Brazil Nepheline, also called nephelite (from Greek: nephos, cloud), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. ... A QAPF diagram is a double triangle diagram which is used to classify igneous rocks based on mineralogic composition. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ...

Chemically, trachyte contains less SiO₂ than rhyolite and more (Na₂O plus K₂O) than dacite. These chemical differences are consistent with the position of trachyte in the TAS classification, and they account for the feldspar-rich mineralogy of the rock type. Rhyolite This page is about a volcanic rock. ... Gray, red, black, altered white/tan, flow-banded pumice dacite poop Dacite (IPA: ) is a high-silica igneous, volcanic rock. ... The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali content and the silica content. ...

Trachytes usually consist mainly of sanidine feldspar. Very often they have minute irregular steam cavities which make the broken surfaces of specimens of these rocks rough and irregular, and from this character they have derived their name. It was first given to certain rocks of this class from Auvergne, and was long used in a much wider sense than that defined above, in fact it included quartz-trachytes (now known as liparites and rhyolites) and oligoclase-trachytes, which are now more properly assigned to andesites. The trachytes are often described as being the volcanic equivalents of the plutonic syenites. Their dominant mineral, sanidine feldspar, very commonly occurs in two generations, i.e. both as large well-shaped porphyritic crystals and in smaller imperfect rods or laths forming a finely crystalline groundmass. With this there is practically always a smaller amount of plagioclase, usually oligoclase; but the potash felspar (sanidine) often contains a considerable proportion of the sodium feldspar (albite), and has rather the characteristics of anorthoclase or cryptoperthite than of pure sanidine. Rhomb porphyry is an example with usually large porphyritic rhomb shaped phenocrysts enbedded in a very fine grained matrix. Sanidine is the high temperature form of potassium feldspar ((K,Na)(Si,Al)4O8) which occurs in felsic volcanic rocks such as rhyolite and trachyte. ... Rhyolite This page is about a volcanic rock. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Pluton redirects here. ... Rhomb porphyry from the Oslo rift area in Norway Rhomb porphyry is a volcanic rock with gray-white large porphyritic rhomb shaped phenocrysts enbedded in a very fine grained red-brown matrix. ... (For other meanings of Porphyr, see Porphyry) The baptismal font in the Cathedral of Magdeburg is made of rose porphyry from a site near Assuan, Egypt Porphyry is a very hard red, green or purple igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a... For other uses of the word rhombus, see Rhombus (disambiguation) This shape is a rhombus In geometry, a rhombus (or rhomb; plural rhombi) is a quadrilateral in which all of the sides are of equal length, i. ... A phenocryst is a relatively large and usually conspicuous crystal formed in the mass of a porphyritic igneous rock. ...

Quartz is typically rare in trachyte, but tridymite (which likewise consists of silica) is by no means uncommon. It is rarely in crystals large enough to, be visible without the aid of the microscope, but in thin sections it may appear as small hexagonal plates, which overlap and form dense aggregates, like a mosaic or like the tiles on a roof. They often cover the surfaces of the larger feldspars or line the steam cavities of the rock, where they may be mingled with amorphous opal or fibrous chalcedony. In the older trachytes, secondary quartz is not rare, and probably sometimes results from the recrystallization of tridymite. Tridymite Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Robert Hookes microscope (1665) - an engineered device used to study living systems. ... For other articles with similar names, see Opal (disambiguation). ... Chalcedony knife, AD 1000-1200 Bloodstone redirects here. ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ...

Of the mafic minerals present, augite is the most common. It is usually of pale green color, and its small crystals are often very perfect in form. Brown hornblende and biotite occur also, and are usually surrounded by black corrosion borders composed of magnetite and pyroxene; Sometimes the replacement is complete and no bornblende or biotite is left, though the outlines of the cluster of magnetite and augite may clearly indicate from which of these minerals it was derived. Olivine is unusual, though found in some trachytes, like those of the Arso in Isthia. Basic varieties of plagioclase, such as labradorite, are known also as phenocrysts in some Italian trachytes. Dark brown varieties of augite and rhombic pyroxene (hypersthene or bronzite) have been observed but are not common. Apatite, zircon and magnetite are practically always present as accessory minerals. In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Amphibole (Hornblende) Hornblende is a complex inosilicate series of minerals. ... // Headline text Magnetite is a ferrimagnetic mineral form of iron(II,III) oxide, with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Hypersthene is a common rock-forming mineral belonging to the group of orthorhombic pyroxenes. ... Bronzite is a member of the pyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group. ... ske| Fracture|| Conchoidal to even Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. ... Zircon is a mineral belonging to the group of nesosilicates. ...

The trachytes being very rich in potash feldspar, necessarily contain considerable amounts of alkali; in this character they approach the phonolites. Occasionally minerals of the feldspathoid group, such as nepheline, sodalite and leucite, occur, and rocks of this kind are known as phonolitic trachytes. The sodium-bearing amphiboles and pyroxenes so characteristic of the phonolites may also be found in some trachytes; thus aegirine or aegirone augite forms outgrowths on diopside crystals, and riebeckite may be present in spongy growths among the feldspars of the groundmass (as in the trachyte of Berkum on the Rhine). 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 tabular form an inch or two in length scattered through their fine-grained groundmass. In many trachytes, however, the phenocrysts are few and small, and the groundmass comparatively coarse. The ferromagnesian minerals rarely occur in large crystals, and are usually not conspicuous in hand specimens of these rocks. Two types of groundmass are generally recognized: the trachytic, composed mainly of long, narrow, subparallel rods of sanidine, and the orthophyric, consisting of small, squarish or rectangular prisms of the same mineral. Sometimes granular augite or spongy riebeckite occurs in the groundmass, but as a rule this part of the rock is highly feispathic. 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. Phonolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. ... A big crystal of Nepheline from CanaÃ£ Massif, Brazil Nepheline, also called nephelite (from Greek: nephos, cloud), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. ... Sodalite is a rare, rich royal blue mineral widely enjoyed as an ornamental stone. ... Leucite or amphigene is a rock-forming mineral composed of potassium and aluminium metasilicate KAl(SiO3)2. ... For the logical fallacy, see Amphibology. ... Aegirine is an inosilicate member of the clinopyroxene group. ... Riebeckite is a sodium-rich member of the amphibole group of minerals, chemical formula Na2(Fe,Mg)5Si8O22(OH)2. ... It has been suggested that River Rhine Pollution: November 1986 be merged into this article or section. ... Obsidian from Lake County, Oregon Counterclockwise from top: obsidian, pumice and rhyolite (light color) Obsidian is a rock which is a type of naturally occurring glass, produced by volcanoes (igneous origin) when a felsic lava cools rapidly and freezes without sufficient time for crystal growth (see glass transition temperature). ... // Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Teneriffe is a type of lace from the island of Tenerife. ...

A polished opal on trachyte

Trachytes are well represented among the Tertiary and recent volcanic rocks of Europe. In Britain they occur in Skye as lava flows and as dikes or intrusions, but they are much more common on the continent of Europe, as in the Rhine district and the Eifel, also in Auvergne, Bohemia and the Euganean Hills. In the neighborhoord of Rome, Naples and the island of Ischia trachytic lavas and tuffs are of common occurrence. In the United States trachytes are less frequent, being known in South Dakota (Black Hills). In Iceland, the Azores, Teneriffe and Ascension there are recent trachytic lavas, and rocks of this kind occur also in New South Wales (Cambewarra range), East Africa, Madagascar, Aden and in many other districts. Image File history File linksMetadata Download high-resolution version (807x542, 234 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Trachyte User:Aramgutang/Gallery Metadata This file contains additional information, probably added from the digital camera or scanner... Image File history File linksMetadata Download high-resolution version (807x542, 234 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Trachyte User:Aramgutang/Gallery Metadata This file contains additional information, probably added from the digital camera or scanner... Tertiary geological time interval covers roughly the time span between the demise of the non-avian dinosaurs and beginning of the most recent Ice Age, approximately 65 million to 1. ... World map showing the location of Europe. ... Looking towards Quiraing, Skye. ... In computer programming jargon, lava flow is a problem in which computer code, usually written under less than optimal conditions, is put into production and then built on when still in a developmental state. ... A dike in geology refers to a tabular intrusive igneous body. ... Flag of Bohemia Bohemia (Czech: ; German: ) is a historical region in central Europe, occupying the western and middle thirds of the Czech Republic. ... Nickname: Motto: SPQR: Senatus Populusque Romanus Location of the city of Rome (yellow) within the Province of Rome (red) and region of Lazio (grey) Coordinates: Region Lazio Province Province of Rome Founded 21 April 753 BC Government - Mayor Walter Veltroni Area - City 1,285 kmÂ² (580 sq mi) - Urban 5... â€œNapoliâ€ redirects here. ... The island of Ischia near Naples, Italy. ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Welded tuff at Golden Gate in Yellowstone National Park Tuff (from the Italian tufo) is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. ... Official language(s) English Capital Pierre Largest city Sioux Falls Area Ranked 17th - Total 77,163 sq mi (199,905 kmÂ²) - Width 210 miles (340 km) - Length 380 miles (610 km) - % water 1. ... The Black Hills The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is somewhat of a geological anomalyâ€”accurately described as... Motto (Portuguese for Rather die free than in peace subjugated) Anthem (national) (local) Capital Ponta Delgada1 Angra do HeroÃsmo2 Horta3 Largest city Ponta Delgada Official languages Portuguese Government Autonomous region - President Carlos CÃ©sar Establishment - Settled 1439 - Autonomy 1976 Area - Total 2,333 kmÂ² (n/a) 911 sq mi... This article is about the Ascension of Jesus Christ. ... Capital Sydney Government Constitutional monarchy Governor Professor Marie Bashir Premier Morris Iemma (ALP) Federal representation - House seats 50 - Senate seats 12 Gross State Product (2004-05) - Product ($m) $305,437 (1st) - Product per capita $45,153/person (4th) Population (End of March 2006) - Population 6,817,100 (1st) - Density 8. ... Eastern Africa (UN subregion) East African Community Central African Federation (defunct) geographic, including above East Africa or Eastern Africa is the easternmost region of the African continent, variably defined by geography or geopolitics. ... Port of Aden (around 1910). ...

Among the older volcanic rocks trachytes also are not scarce, though they have often been described under the names orthophyre and orthoclase-porphyry, while trachyte was reserved for Tertiary and recent rocks of similar composition. In England there are Permian trachytes in the Exeter district, and Carboniferous trachytes are found in many parts of the central valley of Scotland. The latter differ in no essential respect from their modern representatives in Italy and the Rhine valley, but their augite and biotite are often repiaced by chlorite and other secondary products. Permian trachytcs occur also in Thuringia and the Saar district in Germany. Motto (French) God and my right Anthem No official anthem - the United Kingdom anthem God Save the Queen is commonly used England() â€“ on the European continent() â€“ in the United Kingdom() Capital (and largest city) London (de facto) Official languages English (de facto) Unified - by Athelstan 927 AD Area - Total 130... The Permian is a geologic period that extends from about 299. ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... Motto (Latin) No one provokes me with impunity Cha togar mfhearg gun dioladh (Scottish Gaelic) Wha daur meddle wi me?(Scots)1 Anthem (Multiple unofficial anthems) Scotlands location in Europe Capital Edinburgh Largest city Glasgow Official languages English, Gaelic and Scots1 Government Constitutional monarchy - Monarch Queen Elizabeth II... It has been suggested that River Rhine Pollution: November 1986 be merged into this article or section. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ...

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. The Palaeozoic is a major division of the geologic timescale, one of four geologic eras. ... For other uses, see strata (novel) and strata title. ... Cornwall (pronounced ; Cornish: ) is a county in south-west England, United Kingdom, on the peninsula that lies to the west of the River Tamar and Devon. ...