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Topic: Extrusive

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	extrusive rock
		The formation of extrusive igneous rock is part of the rock cycle.
		Large amounts of extrusive rock called basalt form at the Earth's ocean ridges from lava that fills the void formed when two tectonic plates spread apart.
		Magmas that give rise to pyroclastic extrusive rocks are explosive because they are viscous.
	www.tiscali.co.uk /reference/encyclopaedia/hutchinson/m0035062.html (385 words)

	Igneous Rock - Search View - MSN Encarta
		Extrusive rocks that have the same chemical composition as granite are called rhyolite and those with the same chemical composition as granodiorite are called dacite.
		Extrusive rocks that have the same chemical composition as diorite or gabbro are called basalt.
		Extrusive rocks that erupt from a main central vent form volcanoes, and these are classified according to their physical form and the type of volcanic activity.
	encarta.msn.com /text_761555655__1/Igneous_Rock.html (2324 words)

	card 7 EXTRUSIVE IGNEOUS ROCKS (Site not responding. Last check: 2007-10-12)
		Such rapid cooling of lava, molten rock at the surface, generally does not allow mineral crystals to grow large enough to be seen with the unaided eye, so extrusive rocks are usually fine-grained (also called aphanitic) in their texture.
		This forms the extrusive rock called pumice, which is so light that it floats on water.
		Picture 7 shows the extrusive rock called obsidian which is characterized by its glassy texture.
	seis.natsci.csulb.edu /basicgeo/EXTRUSIVE/EXTRUSIVE.html (502 words)

	Jour. Geophysical Research 1996 (Site not responding. Last check: 2007-10-12)
		Extrusive basalts form the majority of seafloor rock samples and are typically strongly magnetized, supporting the contention that they comprise the primary source of magnetic anomalies.
		Extrusive lavas also decrease in magnetization with age due to low-temperature oxidation [Irving, 1970; Johnson and Atwater, 1977; Bleil and Peterson, 1983; Johnson and Pariso, 1993], which suggests that the extrusive contribution to the magnetic signal becomes less important with age [Cande and Kent, 1976; Blakely, 1983; Raymond and LaBrecque, 1987].
		The extrusive section is also reversely magnetized, in keeping with the predicted age of this crustal section, although several profiles also show a zone of apparent positive magnetization at the base of the extrusive layer.
	deeptow.whoi.edu /jgr96.html (12815 words)

	extrusive - Search Results - MSN Encarta
		Flood basalts are the most common type of extrusive rock.
		Basalt, the most common variety of volcanic rock, composed almost entirely of dark, fine-grained silicate minerals, chiefly plagioclase feldspar and...
		Andesite, a dark, fine-grained volcanic rock, the extrusive equivalent of diorite.
	ca.encarta.msn.com /extrusive.html (94 words)

	Big Bend: Extrusive Igneous Features (Site not responding. Last check: 2007-10-12)
		Extrusive igneous rock is formed when molten rock reaches and spills over on the surface of the earth.
		Most extrusive rocks exhibit an aphanitic texture, meaning that their crystals are not visible to the unaided eye.
		Some extrusive rocks are riddled with vesicles, small holes in the rock left by gas bubbles during cooling.
	geoweb.tamu.edu /faculty/herbert/bigbend/ig/ext.html (417 words)

	Igneous Rock Page
		EXTRUSIVE IGNEOUS ROCKS Extrusive igneous rock forms when molten rock reaches the earth's surface and cools.
		The quick cooling doesn't allow the formation of large crystals so most extrusive rocks have small crystals or none at all.
		In some extrusive rocks, like pumice and scoria, air and other gases are trapped in the lava as it cools.
	www.usoe.k12.ut.us /curr/science/sciber00/8th/earth/sciber/rocks2.htm (504 words)

	extrusive rock
		The formation of extrusive igneous rock is part of the rock cycle.
		Large amounts of extrusive rock called basalt form at the Earth's ocean ridges from lava that fills the void formed when two tectonic plates spread apart.
		Magmas that give rise to pyroclastic extrusive rocks are explosive because they are viscous.
	storm.lineone.net /reference/encyclopaedia/hutchinson/m0035062.html (385 words)

	Extrusive (geology) Summary
		Magma's volatile components, that is, those substances that tend to separate out at high temperature and low pressure (especially water), are therefore quickly lost by extruded magma, and are not present during crystallization.
		Extrusive refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff.
		The main effect of extrusion is that the magma can cool much more quickly in the open air or under seawater, and there is little time for the growth of crystals.
	www.bookrags.com /Extrusive_(geology) (401 words)

	Utah Geological Survey
		Extrusive igneous rocks solidify from molten material that flows over the earth’s surface (lava).
		Extrusive igneous rocks typically have a fine-grained texture (individual minerals are not visible unless magnified) because the lava cools rapidly when exposed to the atmosphere, preventing crystal growth.
		A 12-square-mile outcrop of granite is visible on the southwestern flank of the Sheeprock Mountains, Tooele and Juab Counties.
	www.ugs.state.ut.us /surveynotes/gladasked/gladrocks.htm (1059 words)

	Igneous Rocks (Site not responding. Last check: 2007-10-12)
		Extrusive igneous rocks forms when molten rock reaches the earth's surface and cools.
		Another kind of extrusive rock is known as pumice.
		Some other common extrusive igneous rocks are Scoria, which is like basalt but has a lot more air bubbles trapped in the rock, and Rhyolite a very light colored extrusive igneous rock.
	utahscience.oremjr.alpine.k12.ut.us /Sciber01/8th/rock/html/igneous.htm (420 words)

	Rock Types
		Igneous rocks are sub divided into two types of classifications: extrusive and intrusive.
		Extrusive igneous rocks form when molten rock reaches the earth's surface and cools.
		Some other common extrusive igneous rocks are scoria, which is like basalt but has a lot more air bubbles trapped in the rock, and rhyolite a very light colored extrusive igneous rock.
	www.usoe.k12.ut.us /curr/science/core/8thgrd/sciber8/geology/html/rocktyps.htm (1241 words)

	7a. Igneous Rocks: Forged by Fire [Beyond Books - Earth Science: Part 2]
		Basalt is a mafic extrusive rock composed mostly of pyroxene, feldspar, and, in some cases, olivine.
		The individual crystals of extrusive rocks such as basalt are too small to be seen with the unaided eye because of the rapid cooling that extrusive magmas undergo to form rocks.
		Another common extrusive igneous rock that forms under conditions similar to those for basalt is rhyolite.
	www.beyondbooks.com /ear82/7a.asp?pf=on (743 words)

	Intrusive and Extrusive Rocks (Site not responding. Last check: 2007-10-12)
		Rocks with visible crystals of roughly the same size are said to have a phaneritic texture.
		Igneous rocks which form by the crystallization of magma at the surface of the Earth are called extrusive rocks.
		They are characterized by fine-grained textures because their rapid cooling at or near the surface did not provide enough time for large crystals to grow.
	hyperphysics.phy-astr.gsu.edu /hbase/geophys/intrus.html (134 words)

	Geology : Igneous Rocks (Intrusive & Extrusive) (Site not responding. Last check: 2007-10-12)
		Extrusive rocks are formed when lava flows or is thrown from a volcano.
		Because the lava cools more quickly, the crystals have little or no time to grow, and the crystals in the rocks can only be seen with a microscope.
		Examples of extrusive igneous rocks are pumice, ash, tuff, obsidian, basalt, andesite, dacite, and rhyolite and volcanic glass.
	schoolscience.rice.edu /science/curricula/PrintPreviewLearningExperienceOnly.cfm?LEID=2008&CurriculaID=314 (357 words)

	Rocks, Minerals, & Plate Techtonics!!!!!!!!!!!!!!!!! continued.................. (Site not responding. Last check: 2007-10-12)
		Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface.
		The change in the rate of cooling may occur as magma moves nearer to the surface.
		Extrusive rocks have a fine-grained or glassy texture.
	hometown.aol.com /spongedudex721/myhomepage/personal.html (1401 words)

	Extrusive Igneous Rocks
		Extrusive igneous rocks, or volcanics, form when magma makes its way to Earth's surface.
		Often, lava cools over a few days to weeks and minerals have enough time to form but not time to grow into large crystals.
		Basalt is the most common type of extrusive igneous rock and the most common rock type at the Earth's surface.
	www.windows.ucar.edu /tour/link=/earth/geology/ig_extrusive.html (190 words)

	Extrusive Igneous Rocks
		Extrusive igneous rocks, or volcanics, are formed when magma makes its way to Earth's surface, erupts or flows above the surface as lava, and then cools forming rock.
		The lava that erupts onto the Earth's surface can come from different levels of the Earth's upper mantle, between 50 km and 150 km below the surface.
		Find out more about extrusive igneous rocks by visiting our intermediate level page!
	www.windows.ucar.edu /earth/geology/ig_extrusive.backup_MetaRefresh (473 words)

	Petrographic Characteristics of Extrusive Rocks from Hruskovec, Mt. Kalnik, NW Croatia, Geologia Croatica, 47/2, ... (Site not responding. Last check: 2007-10-12)
		Petrographic Characteristics of Extrusive Rocks from Hruskovec, Mt. Kalnik, NW Croatia, Geologia Croatica, 47/2, 181-191, Zagreb, 1994
		The contacts of the extrusives with surrounding sediments suggest an Upper Cretaceous age for the volcanism.
		The rocks resemble the extrusives found in other parts of Mt. Kalnik, as well as the extrusives from the wider area of NW Croatia and the rocks found in ophiolitic complexes of the Internal Dinarides.
	www.geologia-croatica.hr /abstract/gc-47-2-04.html (171 words)

	Physical Geology Lab Samples (Site not responding. Last check: 2007-10-12)
		Andesite is an extrusive volcanic rock with a composition that is intermediate between basalt and rhyolite.
		Obsidian is an extrusive volcanic rock formed by the rapid cooling of high viscosity magma.
		Scoria is a dark-colored extrusive volcanic rock with abundant large vesicles.
	itc.gsw.edu /faculty/tweiland/igrx.htm (278 words)

	Sorptive Mineral Institute, a Trade Association for Absorbent Clay Manufacturers, Marketers, and Processors
		Montmorillonite is a layered silicate belonging to the smectite group of phyllosilicate minerals.
		It is formed primarily by the alteration of extrusive volcanic rocks such as volcanic ash falls and ash fall tuffs.
		Active membership in the Sorptive Minerals Institute (SMI) is open to any firm or corporation that produces and/or sells sorptive minerals, which are defined to include a variety of clays, specifically attapulgite, bentonite, diatomite and montmorillonite.
	www.sorptive.org (220 words)

	Extrusive Rocks: Petrography (Site not responding. Last check: 2007-10-12)
		The classification schemes for the common extrusive rock types are shown in the linked pages below.
		Pyroclastic rocks are generally classified according to the grain size.
		After the norm is determined, as you can tell by looking at the overlapping fields of andesite and basalt, further refinement is necessary.
	www.eos.ubc.ca /courses/eosc221/igneous/extru/expetro.html (97 words)

	extrusive - OneLook Dictionary Search
		Tip: Click on the first link on a line below to go directly to a page where "extrusive" is defined.
		Extrusive : Online Plain Text English Dictionary [home, info]
		Phrases that include extrusive: extrusive rock, extrusive bedrock
	www.onelook.com /?w=extrusive&ls=a (167 words)

	Quiz on Rocks Overview and Igneous Rocks
		Extrusive igneous rocks have smaller crystals than intrusive igneous rocks because _______.
		Extrusive igneous rocks cool slower than intrusive rocks
		Extrusive igneous rocks melt slower than intrusive rocks
	www.oswego.edu /~gabel/q1igrx.html (543 words)

	Geography4Kids.com: Earth Structure: Rock Types
		There are the rocks that make it to the surface (extrusive) and the ones that are stuck in the crust just below the surface (intrusive).
		These igneous types have all hardened after being molten rock.
		The intrusive types are usually found in areas called plutons and dikes, big old pools of molten rock that were just beneath the surface.
	www.geography4kids.com /files/earth_rocktypes.html (669 words)

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