Andesite
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Andesite 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 to porphyritic in textu
A sample of andesite (dark groundmass) with amygdaloidal vesicles filled with zeolite. Diameter of view is 8 cm.
QAPF diagram with basalt/andesite field highlighted in yellow. Andesite is distinguished from basalt by SiO2 > 52%.
Block lava at Fantastic Lava Beds near Cinder Cone in Lassen Volcanic National Park
Photomicrograph of andesite in thin section (between crossed polarizers)
Diorite
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Diorite is an intrusive igneous rock formed by the slow cooling underground of magma that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composit
Andesite
…in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende. Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is…
Orbicular diorite from Corsica (corsite)
Hornblende diorite from the Henry Mountains, Utah, US
Naqada II jar with lug handles; c. 3500–3050 BC; height: 13 cm (5 in); Los Angeles County Museum of Art (US)
Statue of Gudea I, dedicated to the god Ningishzida; 2120 BC (the Neo-Sumerian period); height: 46 cm (20 in), width: 33 cm (10 in), depth: 22.5 cm (8.9 in); Louvre