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Topic: Extrusive geology

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	Jour. Geophysical Research 1996 (Site not responding. Last check: 2007-10-18)
		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)

	What are igneous rocks? (Site not responding. Last check: 2007-10-18)
		Extrusive, or volcanic, igneous rock is produced when magma exits and cools outside of, or very near the Earth's surface.
		Extrusive rocks are more difficult to clearly identify because the mineral grains are typically invisible.
		Rhyolite (a felsic extrusive rock) has the same mineral composition as granite (an intrusive igneous rock) and is composed dominantly of the minerals potassium feldspar (K-spar), quartz, and lesser amounts of plagioclase feldspar, mica, hornblende, and other minerals.
	interactive2.usgs.gov /faq/list_faq_by_category/get_answer.asp?id=502 (870 words)

	Igneous Rock Identification Exercise (Site not responding. Last check: 2007-10-18)
		The deep-seated plutonic rocks can be exposed at the surface for study only after a long period of weathering or by some tectonic forces that push the crust upward or by a combination of the two.
		Extrusive rocks occur in two forms: (1) as lava flows that flood the land surface much like a river and (2) as fragmented pieces of magma of various sizes (pyroclastic materials), which often are blown through the atmosphere and blanket the Earth's surface upon settling.
		Both intrusive and extrusive magmas have played a vital role in the spreading of the ocean basin, in the formation of the oceanic crust, and in the formation of the continental margins.
	geology.csupomona.edu /alert/igneous/ignrxs.htm (1238 words)

	Extrusive (geology) (Site not responding. Last check: 2007-10-18)
		Extrusive refers to a mode of igneous rock (geology) formation, in which hot magma from inside the Earth flows out (extrudes) onto the surface.
		The main effect of extrusion is that the magma can cool much more quickly in the open air, and there is little time for the growth of crystals.
		Often, a residual portion of the matrix (geology) fails to crystallize at all, instead becoming an interstitial obsidian.
	read-and-go.hopto.org /Volcanology/Extrusive-(geology).html (96 words)

	[No title]
		Extrusive igneous rocks (of volcanic origin) take on a texture consistent with the manner or eruption, such as frothy or blocky lava rock, a condensed volcanic ash, or even natural glass (obsidian).
		Extrusive Igneous Rocks Extrusive igneous rocks form from the cooling of molten material that has erupted on the surface of the Earth, as in a volcanic eruption.
		The rock is chiefly of rhyolite and andesite composition, and has the texture of a breccia or tuff, an extrusive igneous rock with a rough, sometimes frothy texture and a chemical and mineralogical composition similar to granite (rich in silica and aluminum oxides).
	geopubs.wr.usgs.gov /bulletin/b2195/b2195.txt (21237 words)

	Igneous Landforms -- The Slackpacker's Geology Primer
		Rock resulting from extrusive activity such as pumice, "lava rock" etc. frequently shows evidence of the outgassing that occurs as the magma cools.
		Some igneous forms in canyons are extrusive, such as the lava flow in the western portion of Grand Canyon NP; the lava flowed after the canyon had been formed.
		The Geology List These are the geological wonders everyone should see while visiting this planet.
	www.slackpacker.com /igneous.html (1498 words)

	Bryce Canyon National Park: GEODETECTIVE Program (Site not responding. Last check: 2007-10-18)
		A common example of an extrusive igneous rock is basalt.
		Some extrusive rocks, such as obsidian and pumice, cool so rapidly that they completely lack crystal structure and are considered a volcanic glass.
		The goal is to create 'extrusive' rocks, where either no or few crystals were formed, 'intrusive' rocks where large crystals were formed, and for more advanced students, porphyritic or vesicular rocks were formed.
	www.nps.gov /brca/geodet/geodet_inorout.html (1135 words)

	SDSU - Department of Geological Sciences - Local Geology (Site not responding. Last check: 2007-10-18)
		It is known that around the SDSU campus the oldest rocks exposed are igneous extrusive, although just outside of the campus area there are also igneous intrusive rocks.
		These extrusive rocks are volcanic basalts that have been named - in accord with standard geologic practice - the Santiago Peak Formation (show me).
		Another way to depict the geology of a region is by using a vertical representation to indicate the relative and numerical ages of the rocks.
	www.geology.sdsu.edu /localgeology/sadiegogeology.htm (1038 words)

	Geology 208: Quiz #1
		The dark, aphanitic, extrusive rock that has a silica content of about 60% and is the second most abundant volcanic rock.
		It is intermediate in composition (half-way between felsic and mafic) and is the extrusive equivalent of diorite.
		The fine-grained volcanic or extrusive equivalent of granite, light brown to gray and compact.
	spot.pcc.edu /~ksutton/GEO208/208glossary.html (1170 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)

	NMBGMR Circular 158 (Site not responding. Last check: 2007-10-18)
		Numerous reports on the geology of the central Peloncillo Mountains-including studies of the sedimentary and igneous rocks, structure, and mineral resources-have been published over the last 120 years.
		The central Peloncillo Mountains consist of a broken, faulted arch of Precambrian to middle Tertiary extrusive and intrusive igneous rocks and sedimentary rocks overlain to the north and south by middle Tertiary and younger extrusive volcanic rocks.
		The andesite extrusives are cut by the granite porphyry and quartz-latite porphyry dikes and sills.
	geoinfo.nmt.edu /publications/circulars/158/home.html (435 words)

	Glossary (Site not responding. Last check: 2007-10-18)
		In geology, a mineral is a specific, naturally ocurring, crystalline substance.
		A fine-grained, extrusive igneous rock of the same composition as granite.
		In geology, weathering is the breakdown of rock into smaller pieces, or into different substances, by mechanical and chemical processes.
	home.comcast.net /~bollesg/geology/glossary.html (909 words)

	Views of the National Parks (Site not responding. Last check: 2007-10-18)
		Geology is the study of rocks, how they form, and the processes that shape Earth.
		IMPACT – the Geology of Washington, D.C. From hills and valleys to mountains and beaches, geology has left its impact on the Washington, D.C. area by shaping the diverse terrain found within it.
		Geology has changed the landscape and waterways, and influenced the development of the area.
	www2.nature.nps.gov /views/Sites/NAMA/HTML/ET_NamaTour1.htm (1900 words)

	Boy Scout Geology Merit Badge (Site not responding. Last check: 2007-10-18)
		Welcome to Rockhounding Arkansas, and if you are just surfing in, you might like to start at the beginning and have a look around.
		ERE ARE thirteen requirements for the Geology badge, shown below in brown type.
		Geology is the science that studies the earth and the rocks it is made of, and the changes and processes the earth has had and is now experiencing.
	rockhoundingar.com /pebblepups/meritbadge.html (857 words)

	Igneous Rock Types and Textures (Site not responding. Last check: 2007-10-18)
		Aphanitic texture -- basalt: This is a volcanic (or extrusive) igneous rock.
		Vesicular texture -- basalt scoria: This is an extrusive igneous rock that chilled very quickly, so that the bubbles (vesicles) formed by escaping gas were preserved.
		Pyroclastic texture -- rhyolite tuff: This is an extrusive rock formed by fragments of hot volcanic rock and crystals blasted out of a volcano and welded together by the heat after the particles came to rest.
	www.humboldt.edu /~geodept/geology108/igneous_rocks.html (352 words)

	Igneous
		a fine-grained (extrusive) igneous rock composed primarily of quartz, potassium feldspar, plagioclase feldspars and some ferromagnesians (compare with granite)
		a fine-grained (extrusive) igneous rock composed of plagioclase feldspars and up to 50% ferromagnesians (compare with diorite)
		a fine-grained (extrusive) igneous rock composed primarily of ferromagnesians with up to 50% plagioclase feldspars (compare with gabbro)
	www.geocities.com /jghist/Glossary/igneous.htm (101 words)

	Geology Department and Courses (Site not responding. Last check: 2007-10-18)
		The geology program prepares students for careers such as: geologist with oil and coal industry, teacher of geology or earth science in high school or college, writer or lecturer in parachurch work, research geologist with governmental agency, independent consultant in the private sector.
		Prerequisite: one undergraduate physical geology course and proficiency in algebra, trigonometry, and vectors.
		Emphasis will be placed on the identification of all types of extrusive (volcanic) and intrusive (plutonic) igneous rocks at both hand specimen and microscope thin section scales.
	www.icr.edu /geology (1020 words)

	Geology of South Dakota
		The scientific study of South Dakota's geology is ongoing.
		Geology of the Black Hills, South Dakota and Wyoming edited by F.J. Rich, 1985.
		Geology Department, S.D. School of Mines and Technology, Rapid City, SD 57701.
	www.northern.edu /natsource/EARTH/Geolog1.htm (1514 words)

	Search Results for rock - Encyclopædia Britannica
		Such aggregates constitute the basic unit of which the solid Earth is comprised and typically form recognizable and...
		in geology, igneous rock that is dominated by the silicates pyroxene, amphibole, olivine, and mica.
		In geology, a naturally occurring and coherent aggregate of minerals.
	www.britannica.com /search?query=rock&submit=Find&source=MWTEXT (504 words)

	Test #1 (Site not responding. Last check: 2007-10-18)
		F The term pahoehoe refers to a lava flow with a surface of rough, angular blocks and fragments.
		F A batholith is generally composed of extrusive rocks.
		F Physical geology is completely distinct from historical geology.
	www.mines.uidaho.edu /~sprenke/Geol101/Test_Answers/Test1__Answers.htm (681 words)

	Big Bend Virtual Field Trip: Introduction
		The Big Bend Virtual Field Trip was created for an independent study project for the Texas A&M University Department of Geology & Geophysics under the supervision of Dr.
		During the week of Spring Break 1996, we visited Big Bend for the purpose of researching the geology of the park and taking pictures of pertinent geologic features.
		The project was supervised by Dr. Bruce Herbert, a professor in Texas A&M University's Department of Geology.
	geoweb.tamu.edu /faculty/herbert/bigbend/intro (231 words)

	Physical Geology Lab Samples
		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)

	Glossary of Geologic Terms
		It is usually extrusive (solidifying from magma) or occasionally intrusive in narrow dikes.
		The concept of stratigraphy includes some of the most important tenets in geology: that sedimentary strata were originally deposited horizontally, that older beds underlie younger beds, and that older rocks are cross-cut by younger ones.
		trap In petroleum geology, a trap is a place in the subsurface to which oil or natural gas migrates, and from which it cannot migrate any further.
	www.gravmag.com /primer.html (1336 words)

	GEOS110 Study Guide Chapter 19 (text only) (Site not responding. Last check: 2007-10-18)
		Characterize the mid-ocean ridge with respect to boundary type, tectonic activity, landforms, heat flow, earthquake-focus depth, and composition of volcanic extrusive rocks.
		Characterize the oceanic trenches with respect to tectonic activity, landforms, heat flow, earthquake-focus depth, and composition of volcanic extrusive rocks.
		Account for the relative crustal movements and the location of earthquake foci in a transform fault associated with a fracture zone crossing the mid-ocean ridges.
	www.lhup.edu /jway/110/110sg.19.htm (573 words)

	UCMP Glossary: Geology
		Lakes formed as water fills a hole formerly occupied by a block of stranded ice.
		lava -- Any molten material that is extrusive or volcanic, or the rock that forms from a molten extrusive.
		Molten rock generated within the Earth; forms intrusive (solidifies below the surface) and extrusive (solidifies above the surface) igneous rocks.
	www.ucmp.berkeley.edu /glossary/gloss2geol.html (3545 words)

	BC Biodiversity Pages - BC Geology
		BC Geology, Rocks and Minerals of BC, igneous rocks, basalt, fold lines, quartz veins, natural springs, geologic history of BC
		BC then is a land of constant geologic change that has produced a land teeming with unique biological diversity.
		Above: A small quartz vein embedded in igneous rock, Right: a much larger piece of the quartz vein embedded in igneous rock but this one is still beneath the surface of the water in Chapman Creek, the creekbed there cuts through a large portion of this.
	www.bcbiodiversity.homestead.com /bcgeology.html (240 words)

	Physical Geology Notes (Site not responding. Last check: 2007-10-18)
		Because they cool more slowly than extrusive rocks, intrusive igneous rocks are generally coarse-grained (>1mm).
		The same compositional variation seen in extrusive rocks is seen in intrusive rocks, but the rocks are given different names:
		Ultramafic extrusive rocks are very rare and most ultramafic rocks are the residue of partial melting.
	ruby.colorado.edu /~smyth/G1010-04.html (271 words)

	SDTV: Episode Resources - Geology
		succession — A fundamental principle of geology, which states that unless disturbed, the oldest fossils in a rock bed should be at the bottom.
		lateral continuity — A fundamental principle of geology, which states that sediments are deposited initially in a layer that extends horizontally in all directions.
		A fundamental principle of geology, which states that if a rock bed hasn't been disturbed since it was formed, it is younger than the layer of rock below it.
	www.pbs.org /standarddeviantstv/episode_res_geology.html (853 words)

	Geology
		"Geology is the window from the past we use to see the future."
		NOTE: The Geology Merit Badge requirements were redone during the summer of 2005.
		The scientific study of the Earth, its origins and evolution, the materials that make it up, and the processes that act on it.
	www.relia.net /~thedane/geology.html (1203 words)

	GLY 220 Physical Geology Notes
		GLY 220 - Physical Geology, Paul Howell, University of Kentucky.
		Pyroclastic — Rock made of pyroclasts: Tuff (ash) and breccia (coarser grained pyroclasts) are the common pyroclastic rocks.
		Extrusive only, can be considered a “sedimentary” igneous rock (pyroclasts as transported sediments, in a way).
	www.uky.edu /AS/Geology/howell/220/notes4B-igneous-part2.html (1523 words)

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