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Felsic. In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. [1] It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen ...
Felsic or silicic magmas have a silica content greater than 63%. They include rhyolite and dacite magmas. With such a high silica content, these magmas are extremely viscous, ranging from 10 8 cP (10 5 Pa⋅s) for hot rhyolite magma at 1,200 °C (2,190 °F) to 10 11 cP (10 8 Pa⋅s) for cool rhyolite magma at 800 °C (1,470 °F). [ 21 ]
Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera. As a volcano extrudes silicic lava, it can form an inflation dome or endogenous dome, gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble.
The magma forming this lava is often felsic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less viscous mafic magma. [2] Extensive felsic lava flows are uncommon, but have traveled as far as 15 km (9 mi).
In geology, an igneous intrusion (or intrusive body[1] or simply intrusion[2]) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; [3] the ...
Dacite (/ ˈdeɪsaɪt /) is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. It is composed predominantly of plagioclase feldspar and quartz.
As magma forms, the initial melt is composed of the more silicic phases that have a lower melting point. This leads to partial melting and further segregation of the lithosphere. In addition the silicic continental crust is relatively buoyant and is not usually subducted back into the mantle. So over time the continental masses grow larger and ...
Rhyolite (/ ˈraɪ.əlaɪt / RY-ə-lyte) [1][2][3][4] is the most silica -rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase.