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extrusive rock
(redirected from extrusive)

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extrusive rock

Any 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)
volcanic rock


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This can happen above ground as with volcanoes it is then called extrusive.
Igneous Rocks by Claudia Mann / Reference and Education community
For example, it has long been thought that the primary source of marine magnetic anomalies lies in the upper, extrusive section of the oceanic crust.
Discovery of "megamullions" reveals gateways into the ocean crust and ... by Tucholke, Brian E. / Oceanus
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).
Deep source of magnetic stripes by Weisburd, Stefi / Science News
 
 
 
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