Andesite
"Andesite is
named after the Andes mountains in South America.."
It is an extrusive igneous rock that forms from explosive stratovolcanoes. This means the rock is reasonably silica-rich and the magma hasn't contained much volatiles.
It can be fine grained, porphyritic or amyglaloidal. Its minerals are mainly andesine and oligoclase, but some biotite or pyroxene also tends to be present. It does not contain any quartz, unlike the closely related rhyolite. If a magma of the same composition would form an intrusive igneous rock, it would be diorite.
Andesitic volcanoes tend to be on or near subduction zones, something that helps to find ancient subduction zones. Some more known of such volcanoes are Mount Fuji in Japan, and Krakatau in Indonesia.
By kamoda
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