Lesson Plan - Get It!
Wow! What do you see happening in the picture above? Can rocks melt like ice and crayons in the sun?
The picture at the beginning of this lesson shows a volcano erupting!
You could see the lava pouring down the outside of a volcano. Before a volcano erupts, it has magma beneath its surface. Magma is simply lava inside the Earth. Once it is on the outside of the Earth, it is referred to as lava. When magma or lava cools, igneous rocks are formed.
Before moving on, if you missed or would like to review the first Related Lesson in this Rocks series, find it in the right-hand sidebar.
Different types of igneous rocks form when the magma or lava cools. How quickly the hot molten liquid cools, and the types of chemicals that were in the liquid, impact the type of igneous rock that will form. Where the liquid cools also affects the type of igneous rock that will be formed.
Extrusive igneous rocks form when magma from inside the volcano rises to the surface of the Earth as lava and cools. This lava cools very quickly. Extrusive igneous rocks generally have pores. If you look at the pumice stone below, you can see lots of pores (holes). Some examples of extrusive igneous rocks are basalt and pumice. Basalt is used to build statues and buildings. Pumice can be used to make cement. You can see a pumice stone pictured below:
Intrusive igneous rocks form when magma cools while it is still beneath the Earth's surface. These take much longer to form than extrusive igneous rocks. Intrusive igneous rocks generally are smooth rocks with shiny crystals mixed into them. Granite, diorite, dunite, and gabbro are all examples of intrusive igneous rocks. Granite is one you probably have heard of before. It can be used to make countertops, pillars, and monuments. You can see different types of granite pictured below. This granite will be used to make counter tops:
You learned about ways igneous rocks can be formed.
Before moving on to the Got It? section, tell your parent or teacher what the difference is between intrusive and extrusive igneous rocks.