1. 3.4 – Igneous and Metamorphic Rocks
Essential Questions:
How Do Geologists Classify Igneous Rocks?
What Are Metamorphic Rocks?

2. How Do Geologists Classify Igneous Rocks?
Igneous rocks are classified by their origin, texture, and mineral composition.

3. Origin
Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface.
Basalt

4. Origin
Intrusive rocks are formed when the magma beneath Earth’s surface cools and hardens.
Granite
Why is this granite intrusion above Earth’s surface?

5. Texture Texture depends on the size and shape of the mineral crystals.
Crystal size depends on cooling rates.

6. Mineral Composition
The amount of silica determines an igneous rocks color.

7. Uses of Igneous Rocks
Igneous rocks tend to be hard, dense, and durable.
Building material
Tools
Landscaping

8. What Are Metamorphic Rocks?
Deep inside Earth, pressure and temperature are high.
Any rock that forms from another rock as a result of changes in heat and/or pressure is a metamorphic rock.

9. How Do Metamorphic Rocks Form?
Metamorphic rocks can form from igneous, sedimentary, or other metamorphic rocks.

10. How Do Metamorphic Rocks Form?
Magma inside the Earth can heat rocks to change them.
High pressure deep inside the Earth can also change rocks.
Minerals can become other minerals.
Shapes can change.

11. How Metamorphic Rocks are Classified
Geologists classify metamorphic rocks according to the arrangement of the grains which have changed due to intense heat and pressure.

12. How Metamorphic Rocks are Classified
Rocks can become foliated, flattened and layered. This can change the minerals inside the rocks also.
Granite  Gneiss
Shale  Slate

13. How Metamorphic Rocks Are Used
Marble (from Quartzite, a sedimentary rock made from the mineral quartz) is easy to sculpt and polish.

14. How Metamorphic Rocks Are Used
Slate (a foliated version of the sedimentary rock shale) splits easily into flat pieces and comes in many colors which are good for roofing and old fashioned blackboards.