There are three main types of rocks classified by how they are formed. Igneous rocks form from melted rock and can be either extrusive or intrusive. Extrusive igneous rocks cool quickly on the surface to form fine crystals like basalt and obsidian, while intrusive igneous rocks cool slowly inside the Earth to form larger crystals such as granite and gabbro. The size of crystals in igneous rocks depends on whether they cool quickly on the surface or slowly underground.

1. Igneous Rocks

2. Rock - material made up of one or more minerals 3 groups of rocks classified by HOW they are formed Igneous rock- form from melted rock when hardened

3. Extrusive igneous rocks Formed from lava “exiting” the volcano and cooling quickly Forms fine-grain crystals Andesite Basalt Obsidian Pumice Rhyolite

4. Intrusive igneous rocks Formed when magma “inside” the volcano cools s-l-o-w-l-y Forms large grain crystals Peridotite Gabbro Granite Pegmatitie Diorite

5. Formation Igneous rocks form from cooling magma. If they cool inside the Earth, they are called __________ igneous rocks and have _______ crystals. If they cool on the surface, they are called __________ igneous rocks and have _______ crystals. intrusive large extrusive small

6. Crystal Size This piece of obsidian cooled so _____ on the surface that it did not have time to form any crystals. fast

7. Crystal Size This piece of rhyolite also cooled on the surface very fast and has ______ crystals. small

8. Crystal Size This piece of granite cooled _______ inside the Earth and has ______ crystals. slowly large

9. Classification is based on crystal size and composition.

10. magma igneous rock lava intrusive extrusive

11. small extrusive; small grain size gabbro has a large grain size intrusive; its large grain size