Andesite is a volcanic rock similar to basalt only lighter in color and containing less iron and magnesium than basalt. Often containing phenocrysts (large conspicuous crystals), Andesite is a host rock for Andesine, a precious gemstone. A majority of the Earth’s continental crust is composed of andesitic rocks.
|Rock||Medium to light gray with fine grained impurities.|
|Varies, contains 57-63% SiO2|
Andesite may be used as aggregate or fill, but it is not ideal for concrete applications because it is high in silica, and causes alkali-silica reactivity in the concrete. Andesitic volcanism is associated closely with porphyry copper deposits and it is a host rock for much of the world’s copper ore. Andesite may also be used by geologists to study the history of ancient geosutures.