A List of Extrusive Igneous Rocks
Extrusive rock, any rock derived from magma (molten silicate material) that was poured out or ejected at EarthТs surface. By contrast, intrusive rocks are formed from magma that was forced into older rocks at depth within EarthТs crust; the molten material then slowly solidifies below EarthТs surface, where it may later be exposed through erosion. Jun 02, †Ј Extrusive igneous rocks are formed when the crystallization and solidification of rock material occur on top of the surface. Due to the volcanic eruption that takes the sediment to the surface, the cooling process of extrusive rocks is quick.
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. Extrusive rock. Additional Info. More About Contributors Article History. Print Cite verified Cite. While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter.
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Alternative Titles: extrusive igneous rock, volcanic rock. Reddish volcanic rock on the coast of Tanna Island, Vanuatu.
Read More on This Topic. Examples of rocks used to make absolute age determinations for the Silurian Period include a volcanic breccia dating back to the Llandovery Learn More in these related Britannica articles:. Examples of rocks used to make absolute age determinations for the Silurian Period include a volcanic breccia dating back to the Llandovery Epoch from exfrusive Descon Formation on Esquibel Island in Alaska, ash beds bentonites from the Buildwas Formation at the base ofЕ.
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Extrusibe most lay people have little access toЕ. Such openings are called vesicles, and the rocks in which they occur are said to be vesicular.
Where the openings lie close together and form a large part ofЕ. History at your fingertips. Sign up here to see what happened On This Dayevery day in your inbox! Email address. By signing up, whwt agree to our Privacy Notice. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox.
Examples of Extrusive Igneous Rocks
Jan 07, †Ј Extrusive rocks are igneous rocks that crystallize on the earth's surface. Keep in mind igneous rocks are rocks that crystallize from liquid magma. The .
The solidification of molten rock material produces two basic types of igneous rocks. Extrusive igneous rocks are formed when the crystallization and solidification of rock material occur on top of the surface. Due to the volcanic eruption that takes the sediment to the surface, the cooling process of extrusive rocks is quick. This fast cooling process allows the formation of small crystals, and the cooling process of molten lava may occur so fast that it might form an amorphous glass.
The name Andesite is used to refer to a family of extremely fine grains of extrusive igneous rocks that are usually colored in light or dark grey. Andesites typically take on various shades when they are weathering and may include shades of brown. Some minerals that might be found in andesite rocks may include biotite, pyroxene, or amphibole. Andesites are also known to be rich in plagioclase feldspar minerals. These types of extrusive rocks are usually found in the flow of lava produced by stratovolcanoes.
The cooling of this lava occurs rapidly as any other extrusive rocks, so they form small crystals. Obsidian igneous extrusive rocks are formed when molten rocks cool off so rapidly on the surface of the earth and the atoms are not arranged in a crystallized manner. It forms an amorphous material commonly known as Mineraloid.
A mineraloid is a form of volcanic glass that forms a smooth with consistent texture that fractures in a conchoidal manner. Obsidian extrusive rock mostly forms at the surface of the earth, and they could also be formed in several places. Obsidian rocks might be found along the edges of any lava flow, at the edges of a volcanic dome, around a sill, or dike and they also form when molten lava comes in contact with water. Basalt is dark in color and it crystallizes into fine grains.
It also contains a substantial amount of pyroxene and plagioclase minerals. Although Basalt almost always forms extrusive igneous rock on lava flows, it may sometimes take the form of small intrusive rock bodies like the igneous dike and a thin sill.
Basalt as an extrusive rock has vast presence on the surface of the earth. Some of the areas that Basalt is abundant are the oceanic basins on Earth. Basalt is an essential rock due to its abundance on the planet. It is important to note that Basalt also occurs on other solar bides like the moon and Mars. Other events might have triggered these occurrences.
The lunar basalts have some slight difference with the Earth basalt rocks due to the high contents of iron. Igneous rocks in Arches National Park, Utah. Benjamin Elisha Sawe June 2 in Environment.
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