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extrusive rock |
Also found in: Dictionary/thesaurus, Wikipedia, Hutchinson | 0.01 sec. |
extrusive rockAny igneous rock derived from magma that is poured out or ejected at the Earth's surface. Extrusive rocks are usually distinguished from intrusive rocks on the basis of their texture and mineral composition. Lava flows and pyroclastic debris (fragmented volcanic material) are extrusive; they are commonly glassy (e.g., obsidian) or finely crystalline (e.g., basalts and felsites). extrusive rock [ik′strü·siv ′räk] (geology) How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| 4 million cubic km (Coffin and Eldholm, 2001) for combined extrusive (6 million cubic km) and intrusive components (Courtillot and Renne, 2003). But studies of ophiolites suggested that the structure of the crust was more complex: The basalts in the upper, extrusive layer had different compositions and magnetic properties than the underlying layer of so-called sheeted dikes (relicts of the channels used by lavas to get to the surface). He was engaged by the company to examine volcanic extrusive and intrusive rocks and their contact relationships with one another, and to give his opinion as to whether they were pre- or post-mineral in age and whether they were part of a caldera sequence. |
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