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Examples of aphanitic igneous rock include basalt, andesite, and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass with few or no crystals. Examples include obsidian.
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]
Rhyolite is common along convergent plate boundaries, where a slab of oceanic lithosphere is being subducted into the Earth's mantle beneath overriding oceanic or continental lithosphere. It can sometimes be the predominant igneous rock type in these settings. Rhyolite is more common when the overriding lithosphere is continental rather than ...
Rhyodacite – Volcanic rock rich in silica and low in alkali metal oxides – A felsic volcanic rock which is intermediate between a rhyolite and a dacite; Rhyolite – Igneous, volcanic rock, of felsic (silica-rich) composition Comendite – Hard, peralkaline igneous rock, a type of light blue grey rhyolite
Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. Xenoliths can be non-uniform within individual locations, even in areas which are spatially limited, e.g. rhyolite -dominated lava of Niijima volcano ( Japan ) contains two types of gabbroic xenoliths which are of different origin ...
The calc-alkaline magma series is one of two main subdivisions of the subalkaline magma series, the other subalkaline magma series being the tholeiitic series. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it fractionally crystallizes to become a felsic magma, which is low in ...
Examples of this type of dacite outcrop are found in northwestern Montana and northeastern Bulgaria. Nevertheless, because of the moderately high silica content, dacitic magma is quite viscous [9] and therefore prone to explosive eruption. A notorious example of this is Mount St. Helens in which dacite domes formed from previous eruptions.
Resurgent calderas can refill with an eruption of rhyolitic magma to form the extrusive rock rhyolite like the Yellowstone Caldera. [2] Submarine volcanoes erupt on the ocean floor and produce the extrusive rock pumice. [2] Pumice is a light-weight glass with a vesicular texture that differs from scoria in its silicic composition and therefore ...