Figure 4.14: Obsidian is an extrusive igneous rock. It cools so rapidly that crystals do not
form, and it has a glassy texture. ( 20 )
Figure 4.15: These are examples of basalt below the South Pacific Ocean. Basalt is an
extrusive igneous rock common below the oceans, though it is also found in some places on
continents. ( 1 )