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Andesite (/ ˈ æ n d ə z aɪ t /) [1] is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica -poor basalt and silica-rich rhyolite . It is fine-grained ( aphanitic ) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende .
Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase . Basaltic andesite can be found in volcanoes around the world, including in Central America [ 1 ] and the Andes of South America .
A sample of andesite (dark groundmass) with amygdaloidal vesicles filled with zeolite. Diameter of view is 8 cm. Adakite – Volcanic rock type; Andesite – Type of volcanic rock; Alkali feldspar granite – Type of igneous rock rich in alkali feldspar; Anorthosite – Mafic intrusive igneous rock composed predominantly of plagioclase
Rock types of the tholeiitic magma series include tholeiitic basalt, ferro-basalt, tholeiitic basaltic andesite, tholeiitic andesite, dacite and rhyolite. The variety of basalt in the series was originally called tholeiite but the International Union of Geological Sciences recommends that tholeiitic basalt be used in preference to that term. [1]
The breccias in the Fifes Peak are mostly shades of gray, purple, and red, with angular to subrounded rock fragments cemented by ash. The fragments are a few inches in dimension, rarely a foot long. They are mostly andesite porphyry, pumice, and glass. With fewer rock fragments, the breccias is a buff and tan. Pieces of petrified wood may be ...
The andesite line is the most significant regional geologic distinction in the Pacific Ocean basin. It separates the mafic basaltic volcanic rocks of the Central Pacific Basin from the partially submerged continental areas of more felsic andesitic volcanic rock on its margins.
andesite Fine-grained igneous rock of intermediate composition. Up to half of the rock is plagioclase feldspar with the rest being ferromagnesian minerals. angular unconformity An unconformity in which younger strata overlie an erosion surface of tilted or folded layered rock. anorthite. Also called Indianite.
The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. 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 ...