We identify types of rocks by how the rocks form. If you're not sure what type of rock you're holding, look for clues. Because igneous rocks form when magma and lava cool, they often have crystals. Crystals are clear, hard solids. The longer the rock takes to cool, the bigger the crystals will be. Basalt has large crystals because it cools slowly. Other igneous rocks cool so quickly that gas from the magma doesn't have time to escape into the air before the magma turns solid. This leaves some igneous rocks, like scoria, with holes or spaces in them. Igneous rocks rarely contain fossils and are not layered. What do holes in igneous rocks indicate about the cooling process of the magma? A The magma cooled too quickly for gas to escape. B The molten rock cooled slowly. C The magma cooled in layers. D The rock cooled with fossils in each of the holes or spaces.