Extrusive Rocks......From above the surface!
Extrusive igneous rock is rock formed from LAVA that has already erupted onto the surface of the Earth. Lava comes from the top/upper mantle of the crust. . If the lava cools too quickly, the crystals in the newly-formed rock will not be visible. In general, extrusive rocks have small crystals. Basalt is the most abundant extrusive igneous rock on Earth's surface. Basalt forms most of the Earth's surface. Pumice, an extrusive rock, is largely used for abrasives and cleaning supplies.