Andesite

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.

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 gestures.