Igneous rocks earn their name because they are made by fire. Lava, for example, can harden into igneous rocks. Planets Mercury, Venus, and Mars are mostly igneous rocks, and the Moon is entirely igneous rock. In fact, every time a volcano erupts, new igneous rocks are formed. Sections in this colorful book, complete with large pictures, include Igneous Rock Formation, Big-Time Basalt, Great Granite, and Super Silicates. In the latter section.