Basalt is an igneous rock that is formed from the rapid cooling of low- viscosity lava rich in magnesium and iron (mafic lava)
. It is a dark-colored, fine-grained rock composed mainly of plagioclase and pyroxene minerals
. Basalt is usually dark grey to black in color, due to its high content of augite or other dark-colored pyroxene minerals, but can exhibit a wide range of shading. Some basalts are quite light-colored due to a high content of plagioclase, and these are sometimes described as leucobasalts
. Basalt is the most common volcanic rock type on Earth, making up over 90% of all volcanic rock on the planet
