Extrusive rock 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. [1]

Extrusive rock, any rock derived from magma (molten silicate material) that was poured out or ejected at Earth’s surface. By contrast, intrusive rocks are formed from magma that was forced into older rocks at depth within Earth’s crust; the molten …

Extrusive igneous rocks, also known as volcanic rocks, are formed when magma reaches the Earth's surface and cools rapidly. This process occurs when magma from the Earth's mantle rises to the surface through volcanic vents or fissures, resulting in volcanic eruptions.

Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff. Pictures and brief descriptions of some common igneous rock types are shown on this page.

2018年4月13日 · Extrusive rocks and intrusive rocks both form when hot molten material crystallizes. However, extrusive rocks form from lava at the surface of the Earth, whereas intrusive rocks form from magma underground, often relatively deep in the Earth.

2018年10月12日 · An extrusive igneous rocks definition states these rocks form when magma "exits and cools above (or very near) the Earth's surface." Examples of extrusive igneous rocks include basalt, andesite, rhyolite, dacite, obsidian, pumice and scoria.

2018年6月2日 · 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.

2023年7月9日 · Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, and andesite. Obsidian is an example of an extrusive igneous rock that is amorphous or lacks crystalline structure.

Extrusive igneous landforms are the result of magma coming from deep within the earth to the surface, where it cools as lava. This can happen explosively or slowly, depending on the chemical composition of the lava and whether there is an easy path for it to take to the surface.

2019年3月7日 · Extrusive rocks erupt from volcanoes or seafloor fissures, or they freeze at shallow depths. This means that they cool relatively quickly and under low pressures. Therefore, they are typically fine-grained and gassy.