Search results
Results from the WOW.Com Content Network
Rhyolite. 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 ...
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] For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s).
Magma rich in silica and poor in dissolved water is most easily cooled rapidly enough to form volcanic glass. As a result, rhyolite magmas, which are high in silica, can produce tephra composed entirely of volcanic glass and may also form glassy lava flows. [2] Ash-flow tuffs typically consist of countless microscopic shards of volcanic glass. [3]
Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals. It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase. This places andesite in the basalt /andesite field of ...
The Taupō Volcano erupts rhyolite, a viscous magma, with a high silica content, a feature associated with the middle portion of the Taupō Volcanic Zone within the Taupō Rift. This is an intra-arc rift in the eastern part of the continental Australian Plate , resulting from an oblique convergence with the Pacific Plate in the Hikurangi ...
Rhyolitic magma is felsic and the most abundant in silica, potassium, and sodium but the lowest in iron, magnesium, and calcium. [1] [3] The silica composition of rhyolitic magma ranges from 65-75 wt.%. [1] It forms in the lowest temperature range, from about 1200 °F to 1470 °F. [1], [3] Rhyolitic magma has the highest viscosity and gas ...
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.
Rhyolitic magmas generally produce finer grained material compared to basaltic magmas, due to the higher viscosity and therefore explosivity. The proportions of fine ash are higher for silicic explosive eruptions, probably because vesicle size in the pre-eruptive magma is smaller than those in mafic magmas. [ 1 ]