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Andesite is usually light to dark grey in colour, due to its content of hornblende or pyroxene minerals. [2] but can exhibit a wide range of shading. Darker andesite can be challenging to distinguish from basalt, but a common rule of thumb, used away from the laboratory, is that andesite has a color index less than 35. [9]
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] In contrast, intrusive rock refers to rocks formed by magma which cools below the surface. [2]
Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt , andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite ...
For example, andesitic magmatism is associated with the formation of island arcs at convergent plate boundaries while basaltic magmatism is found at mid-ocean ridges during sea-floor spreading at divergent plate boundaries. On Earth, magma forms by partial melting of silicate rocks either in the mantle, continental or oceanic crust. Evidence ...
Magma exists in three main forms that vary in composition. [3] When magma crystallizes within the crust, it forms an extrusive igneous rock. Dependent on the composition of the magma, it may form either rhyolite, andesite, or basalt. [3] Volatiles, particularly water and carbon dioxide, significantly impact the behavior of each form of magma ...
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Intermediate composition magma, such as andesite, tends to form cinder cones of intermingled ash, tuff and lava, and may have a viscosity similar to thick, cold molasses or even rubber when erupted. Felsic magma, such as rhyolite, is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. Volcanoes with rhyolitic ...
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