The mineral composition of andesite is largely plagioclase. Plagioclase is a silicate mineral that goes into forming many types of rock. Another mineral composition of andesite is biotite, which is another silicate mineral that's also a type of mica.
Accessory minerals in andesite include quartz, hornblende, pyroxene, glass, garnet and ilmenite. Andesite can also contain orthoclase. It's considered an intermediate rock, which means it has between 52 and 63 percent silicon dioxide.
Andesite is a fine-grained, igneous rock that's formed out of lava flows. It's usually a blackish-brown or green color, especially if the rock contains a lot of glass. It is often found with basalt and sourced from the Pacific Ocean. It's also part of the crust of the planet Mars. It is abundant in the Andes Mountains, and it is from these mountains that the rock gets its name.
When andesite is abundant in lava, it forms blocks with smooth sides. This is because andesite lava is thick and viscous. Andesite lavas can also form lava domes. They most often erupt from stratovolcanoes, which are steep and cone-shaped like Mt. Fuji.
Where it is plentiful, andesite is used as a building material. It's also a valuable ore of copper.