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.
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The crystals that form do not have time to grow very large, so most extrusive rocks are finely grained. The term includes fine-grained crystalline or glassy rocks formed from hot lava quenched at or near Earth's surface, and those made of welded fragments of ash and glass ejected into the air during a volcanic eruption.
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A photo gallery of intrusive and extrusive rocks by Geology.com ... and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above Earth's surface. Pictures and brief descriptions of some common igneous rock types are shown below.
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Extrusive - Wikipedia, the free encyclopedia
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 fal...
en.wikipedia.org/wiki/Extrusive
Igneous rock - Wikipedia, the free encyclopedia
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Igneous rock (from the Latin ignis meaning fire ) is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma (molten rock) being cool...
en.wikipedia.org/wiki/Igneous_rock
Mafic, felsic, and intermediate extrusive rocks. More general terms for these rocks are mafic, felsic, and intermediate. Mafic rocks have about 50 percent silica and high amounts of iron, magnesium, and calcium and are dark in color.
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They are rocks that have been cooled very quickly and have very small crystals if any at all. Some cooled that they even have holes in them. FORMATION; Magma is pressured and blown out of a volcano or fissure; The magma gets pushed ... I. ROCKS S. ROCKS M. ROCKS EARTH VOLCANO PLATES HOME RETURN TO THINKQUEST...
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Extrusive igneous rocks, or volcanics, form when magma makes its way to Earth's surface. The molten rock erupts or flows above the surface as lava, and then cools forming rock. The lava comes from the upper mantle layer, between 50 km and 150 km below the Earth's surface.
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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.
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