- 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).
* * *▪ geologyany rock derived from magma (q.v.; molten silicate material) that is poured out or ejected at the Earth's surface. By contrast, intrusive rocks are formed from magma that is forced into older rocks at depth within the Earth's crust; the molten material then slowly solidifies below the Earth's surface, where it may later be exposed owing to erosion. Extrusive rocks are usually distinguished from intrusive rocks on the basis of their texture and mineral composition.Both lava flows and pyroclastic debris (fragmented volcanic material) are extrusive; they are commonly glassy (obsidian) or finely crystalline (basalts and felsites). Many extrusive rocks also contain intrusive components; this mixture of fine- and coarse-grained textures is described as porphyritic.
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rock — rock1 rockless, adj. rocklike, adj. /rok/, n. 1. a large mass of stone forming a hill, cliff, promontory, or the like. 2. Geol. a. mineral matter of variable composition, consolidated or unconsolidated, assembled in masses or considerable… … Universalium
Rock — /rok/, n. a male given name. * * * I In geology, a naturally occurring and coherent aggregate of minerals. The three major classes of rock igneous, sedimentary, and metamorphic are based on the processes that formed them. These three classes are… … Universalium
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 fall back as pyroclastics or tuff. This is opposed to… … Wikipedia
extrusive — [ek stro͞o′siv] adj. 1. extruding or tending to extrude 2. Geol. designating or of igneous rock formed from lava that hardened on the surface of the earth, moon, etc.: cf. INTRUSIVE (sense 2) … English World dictionary
Rock cycle — rocks do not remain in equilibrium and are forced to change as they encounter new environments. The rock cycle is an illustration that explains how the 3 rock types are related to each other and how processes change from one type to another over… … Wikipedia
Rock (geology) — In geology, rock is a naturally occurring aggregate of minerals and/or mineraloids.The Earth s outer solid layer, the ‘lithosphere’, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic. The… … Wikipedia
extrusive — 1. adjective Jutting out; extruding. See Also: extrude, extrusion, detrusive, intrusive, protrusive, retrusive 2. noun Rock which has been formed through volcanic extrusion … Wiktionary
extrusive — adj. tending to push out; tending to project; of molten rock that was forced through cracks in the earth s surface … English contemporary dictionary
extrusive — adjective Geology relating to or denoting rock that has been extruded at the earth s surface as lava or other volcanic deposits … English new terms dictionary
extrusive — adjective of rock material; forced out while molten through cracks in the earth s surface • Ant: ↑intrusive • Similar to: ↑volcanic • Derivationally related forms: ↑extrude • Topics: ↑geology … Useful english dictionary