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Topic: Volcanic rocks

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	Volcanic and Geologic Terms
		Accidental: Pyroclastic rocks that are formed from fragments of non-volcanic rocks or from volcanic rocks not related to the erupting volcano.
		Hot Spot: A volcanic center, 60 to 120 miles (100 to 200 km) across and persistent for at least a few tens of million of years, that is thought to be the surface expression of a persistent rising plume of hot mantle material.
		Unconformity: A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic sucession, such as an interruption in continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata.
	volcano.und.nodak.edu /vwdocs/glossary.html (4560 words)

	Colorado Rocks
		For example, igneous rocks formed at depth under high temperature (T) and pressure (P) in the absence of free oxygen and water are bound to change when brought to the surface to face chemical and mechanical weathering, erosion, transport, deposition and diagenesis.
		Volcanic rocks occur in many tectonic settings, including magmatic arcs at subduction zones (as in the Banda Sea at right), seafloor spreading centers, ocean islands, and along continental rifts and other leaky faults.
		Clastic rocks can be categorized in any number of ways, but most classification schemes key on both grain size and composition, which together tell a lot about the source rock, the depositional environment, and all the steps in between.
	www.cliffshade.com /colorado/rocks.htm (9545 words)

	Igneous Rocks
		Igneous rocks (from Latin "ignis" meaning "pertaining to fire") are formed by cooling and solidification of molten rock material and typically represented by an interlocking aggregate of silicate minerals.
		Volcanic pipes and necks are discordant bodies that represent the upper part of the conduit that connects the volcanic vent (crater) with an underlying magma source (magma chamber or reservoir).
		Volcanic necks are erosional remnants of magma that solidified in the pipe or conduit.
	www.geo.ua.edu /intro03/Ignis.html (2192 words)

	Ancient Volcanic Rocks on Vinalhaven Island - Maine Geological Survey
		A variety of volcanic rocks give clues to an ancient past when this part of the earth's crust was being formed.
		Volcanic breccias are formed in explosive volcanic eruptions during which lava and solid rocks of the volcanic vent are blown apart into fragments of different sizes.
		But an important difference is that the rock in Figure 3 has layers in which the fragments have been sorted according to their size.
	www.state.me.us /doc/nrimc/mgs/explore/bedrock/sites/mar98.htm (751 words)

	Volcanoes and volcanic rocks
		Volcanic domes commonly occur within the craters or on the flanks of large composite volcanoes.
		Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption.
		Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme.
	www.rockcollector.co.uk /volcano1.htm (1308 words)

	Class 6 Volcanic Rocks
		To become familiar with the general features of volcanic rocks, their origins, and the types of ore deposits which are associated with them.
		Pyroclastic rocks are usually further subdivided based on the relative proportion of vitric material to crystals to lithic fragments (or rock fragments).
		Classification of pyroclastic volcanic rocks by size of the fragments (from Williams and McBirney, 1979).
	www.dmtcalaska.org /course_dev/explogeo/class06/notes06.html (2123 words)

	Geoscience - The Earth - Shaping the Earth - Volcanism and volcanic rocks
		The pyroclastic material erupted from an explosive volcanic eruption may be ejected as fragments, resulting in scoria cones or ash fall deposits, or charge outwards in ash flow deposits.
		The finer materials of explosive volcanic eruptions are ejected into the air, eventually falling to the ground to form a layer of ash.
		Blocks are angular fragments of solid rock whereas bombs are fragments flung from volcanic vents as pasty blobs of magma that were streamlined as they solidified during their flight.
	www.amonline.net.au /geoscience/earth/volcanism.htm (2940 words)

	Igneous rock - Wikipedia, the free encyclopedia
		Oceanic crust is composed primarily of basalt and gabbro.
		In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of quartz, and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present.
		The texture of volcanic rocks, including the size, shape, orientation, and distribution of grains and the intergrain relationships, will determine whether the rock is termed a tuff, a pyroclastic lava or a simple lava.
	en.wikipedia.org /wiki/Igneous_rock (2737 words)

	USGS Photo Glossary: Volcanic rocks
		The initial distinction between volcanic and plutonic rocks is made on the basis of texture (fine-grained volcanic vs. coarse-grained plutonic).
		Volcanic and plutonic rocks are divided further on the basis of chemistry and mineral composition.
		Different names are given to such slow-cooling plutonic rocks on the basis of chemical composition and mineral proportions (for example, plutonic rocks of basaltic composition are called gabbro).
	volcanoes.usgs.gov /Products/Pglossary/VolRocks.html (563 words)

	USGS Learning Web :: Explorers :: Rocks and Images
		Igneous rocks, also called volcanic rocks, are formed from melted rock that has cooled and solidified.
		When rocks are buried deep within the Earth, they melt because of the high pressure and temperature; the molten rock (called magma) can then flow upward or even be erupted from a volcano onto the Earth's surface.
		Common igneous (volcanic rocks) are basalt, andesite, and rhyolite.
	interactive2.usgs.gov /learningweb/explorer/topic_rocks_igneous.htm (213 words)

	Volcanic rock - Wikipedia, the free encyclopedia
		Volcanic rocks are usually fine-grained or aphanitic to glassy in texture.
		Volcanic rocks are named according to their chemical composition.
		Volcanic rocks often have a vesicular texture, which is the result voids left by volatiles escaping from the molten lava.
	en.wikipedia.org /wiki/Volcanic_rock (250 words)

	CVO Website - Volcanic Rocks (Site not responding. Last check: 2007-10-30)
		On the surface of the Earth, igneous rocks usually occur in a cooled state, except where molten rock is erupting from an active volcano.
		Rocks that crystallize quickly from cooling lava at or near the Earth's surface are called volcanic rocks.
		Common volcanic rocks are basalt, andesite, and rhyolite.
	vulcan.wr.usgs.gov /LivingWith/VolcanicPast/Notes/volcanic_rocks.html (169 words)

	Igneous Rocks
		Stocks may have been feeders for volcanic eruptions, but because large amounts of erosion are required to expose a stock or batholith, the associated volcanic rocks are rarely exposed.
		Melting of dry rocks is similar to melting of dry minerals, melting temperatures increase with increasing pressure, except there is a range of temperature over which there exists a partial melt.
		Melting of rocks containing water or carbon dioxide is similar to melting of wet minerals, melting temperatures initially decrease with increasing pressure, except there is a range of temperature over which there exists a partial melt.
	www.tulane.edu /~sanelson/geol111/igneous.htm (2459 words)

	Igneous Rocks
		The study of igneous rocks is particularly intriguing to geologists because under the microscope, the physical laws of nature are strictly obeyed.
		The idea that rocks of various composition could arise from a single magma was born in the laboratory through the careful study of the sequence in which minerals appear as a melt cools.
		Gabbro is the plutonic equivalent of the volcanic rock basalt.
	www2.brevard.edu /reynoljh/onlinegeology/igneousrocks/igrox.htm (4923 words)

	VOLCANIC ROCKS
		Volcanic rocks are classified by the size, abundance, and type of crystals.
		Volcanic rocks from continental volcanoes can also be identified by their mineralogy.
		This mineral assemblage indicates that the rock is an andesite.
	volcano.und.nodak.edu /vwdocs/vwlessons/volcanic_rocks.html (428 words)

	Volcanic rocks in the Devonian Solund Basin, Western Norway: Large landslides of Silurian (439 Ma) rhyolites Journal of ... (Site not responding. Last check: 2007-10-30)
		This new age constraint, combined with field observations, suggests that the volcanic rocks form part of a 30 km^sup 2^ landslide of rhyolite, granite, gabbro and metasedimentary rocks, rather than extension related volcanism as previously suggested.
		Sedimentary rocks in the Devonian basin are locally folded and cleaved (Nielsen 1968; Sturt & Braathen 2001) and metamorphosed to 230-320 deg C (Svensen et aL 2001).
		Mafic and felsic volcanic rocks associated with fine-grained gabbros and diorites within the Devonian sedimentary rocks near Hersvik were first reported by Kolderup (1926), who inferred that these were emplaced as thrust-sheets of the substrate into the basin sediments (Fig.
	www.findarticles.com /p/articles/mi_qa3721/is_200203/ai_n9044917 (1022 words)

	Alkaline volcanic rocks from the Columbia Hills, Gusev crater, Mars
		Irvine, Backstay, and Wishstone are the type specimens for three classes of fine-grained or fragmental, relatively unaltered rocks with distinctive thermal emission spectra, found as float on the flanks of the Columbia Hills.
		The compositions of all these rocks reveal that the Gusev magmatic province is alkaline, distinct from the subalkaline volcanic rocks thought to dominate most of the planet's surface.
		The fact that differentiated volcanic rocks were not encountered on the plains prior to ascending Husband Hill may suggest a local magma source for volcanism beneath Gusev crater.
	www.agu.org /pubs/crossref/2006/2006JE002698.shtml (430 words)

	EPS 101 Volcanic rocks—
		Volcanic ejecta (tephra) – fragmentary material ejected into the air during a volcanic eruption (pyroclasts).
		Volcanic tuff – volcanic rock formed by the accumulation and lithification (welding) of volcanic ash.
		Volcanic breccia –volcanic rock formed by the accumulation and lithification of larger, angular fragments of pyroclastic debris.
	epswww.unm.edu /facstaff/brearley/eps101/eps101volc.htm (710 words)

	ORE SYSTEMS CONSULTING - Methodology
		Volcanic stratigraphy in the area of the Norbec and East Waite VMS deposits of the Noranda camp, showing their position above the Waite Rhyolite and below the Amulet Andesite.
		The magmatic affinity of a series of volcanic rocks can also be determined, as in the lower plot, where the Ansil mafic to felsic volcanic rocks, in the Noranda area, are of transitional affinity.
		Once the individual volcanic units are identified using their lithogeochemical fingerprints, their 3-D distribution can be plotted.At the Mobrun deposit, sulfide lenses are generally located at the contacts between chemically different rhyolite units.
	www.oresystems.com /method.html (792 words)

	NMBGMR FAQ Volcanoes: Naming Volcanic Rocks
		The naming of volcanic rocks that are calc-alkaline in composition follows the usual basalt-andesite-dacite-rhyolite scheme.
		Geologists use the chemistry of the rocks to help them discern if a rock is derived from magma coming directly from the mantle or if the magma resided in and interacted with the crust before erupting to the surface.
		Rocks with chemistry falling into the orange area can be further subdivided using the lower diagram based on the amount of sodium (Na) relative to potassium (K).
	geoinfo.nmt.edu /faq/volcanoes/igneous_classification.html (580 words)

	Geology of Putah-Cache: Cenozoic Volcanic Rocks (Site not responding. Last check: 2007-10-30)
		The Sonoma volcanic rocks are very well developed in Napa and Sonoma counties (they constitute the principal rock source of the soils of the wine-producing region in and around Napa Valley).
		The source region of the Sonoma Volcanic rocks is uncertain, but it possibly was near the northern end of Napa Valley not far from the town of Calistoga.
		The Clear Lake and Sonoma Volcanics represent the northernmost occurrences of volcanic rocks exposed throughout the California Coast Ranges from the Transverse Ranges (north of Los Angeles) to Clear Lake.
	bioregion.ucdavis.edu /book/10_Clear_Lake/10_07_moores_geo_volc.html (412 words)

	Explaining Why there are Many Types of Volcanic Rocks
		Volcanic and plutonic rocks are both types of igneous rocks.
		The answer is: plutonic rocks (such as granite) cool slowly in a relatively undisturbed environment permitting the growth of large mineral crystals which can easily be seen by the unaided eye.
		Volcanic rocks cool quickly, so the minerals do not have as much time to form large crystals, hence you cannot see minerals in a hand specimen of such rocks as basalt.
	www.msnucleus.org /membership/html/k-6/pt/volcanoes/3/ptv3_1a.html (660 words)

	Volcanic Igenous Rocks Lab
		Geologist believe that volcanism is an important process not only in the formation of the Earth's land surface but other planets and moons as well.
		Other igneous rocks tend to have mostly feldspar and quartz in them which are light colored minerals.
		Fine grained rocks are aphanitic, whereas coarse grained rocks are phaneritic in texture.
	dept.kent.edu /geology/edlab/ign_volcan/volcanics.htm (550 words)

	Titanite in Volcanic Rocks
		We have examined the mineralogy of numerous volcanic ash beds ranging in age from Middle Jurassic to Tertiary from the western U.S. and find some interesting patterns that may be related to changes in the character of the source region.
		Using the titanite extracted from calc-alkaline Tertiary volcanic rocks of known composition, it can be seen that certain elements vary systematically from andesite to dacite to rhyolite.
		Titanite from alkalic volcanic rocks is generally higher in Nb and Fe, but lower in LREEs, Y, and Al when compared to titanite from calc-alkaline rocks (Fig 5).
	geologyindy.byu.edu /faculty/bjk/research/titanite/titanite.htm (2248 words)

	BBC NEWS \| Science/Nature \| World's 'oldest' volcanic rocks
		The rocks lie in Porpoise Cove on the shores of Hudson Bay.
		By calculating the radioactive decay in the rocks' minerals, the scientists estimated their samples to be 3.825 billion years old - give or take 16 million years.
		The Porpoise Cove rocks were recovered as part of a mapping project carried out under the direction of Martin Parent from the Ministry of Natural Resources of Quebec.
	news.bbc.co.uk /1/hi/sci/tech/2546019.stm (521 words)

	Volcanic rocks - Lab #2 (Site not responding. Last check: 2007-10-30)
		Evolution of the Eocene-Paleocene North Atlantic; the Miocene Pacific Northwest: There is evidence for a period of extensional volcanism associated with hotspot activity at about 60 Ma in the vicinity of Iceland in the North Atlantic region.
		Research indicates that the Atlantic MOR is actively spreading today, but that volcanism is in part like that in Hawaii, or like that associated with the Columbia River Basalt Group in the Pacific Northwest.
		However, where erosion has exposed the rocks underlying the flows we can see closely spaced, near-surface dikes or swarms of dikes which apparently served as numerous, closely-spaced conduits for rise of magma to the surface from the mantle.
	darkwing.uoregon.edu /~dogsci/kays/313/volcaniclab.html (1188 words)

	Stop stacking the volcanic rocks (Site not responding. Last check: 2007-10-30)
		Piles of rocks along trails, at overlooks and on lava lakes at the Big Island park are a concern to scientists, who say displacing rocks makes research at the sites more difficult.
		Most rock stacks are at Halemaumau Crater, the southwest rift zone's 1971 flow and the 1982 lava flow, officials said.
		A study on the location of specific types of rocks blasted out of Kilauea gave clues that the volcano had a long history of explosive eruptions, according to the U.S. Geological Survey, which runs the Hawaiian Volcano Observatory within the national park.
	www.post-gazette.com /pg/05321/606433.stm (276 words)

	Volcanic rocks
		The volcanic (igneous) geology blocks relate to the formation of rocks originating from magma (molten rock) according to major periods of mountain building activity, such as during the Caledonian mountain-building episode.
		About 70% of the sites with volcanic (igneous) rock features are accounted for in the report, of which 95% are reported in favourable condition.
		Most localities for igneous rocks are robust (hard rock) and less likely to be affected by activities that are damaging to soft rock or dynamic landscapes.
	www.jncc.gov.uk /page-3585 (634 words)

	Igneous Rocks
		Erosion of a volcano, leaving solidified magma in the conduit as a volcanic neck.
		Collapse of a volcanic summit to form a caldera and perhaps a "crater" lake.
		Isolated masses of rock that were trapped in the magma are called xenoliths (Greek for "foreign stone").
	www.uwgb.edu /dutchs/EarthSC202Notes/igneous.htm (493 words)

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