1. Texture
The look and feel of an object

2. Grains Particles of minerals or other rocks. Large grains Small grains
Coarse feeling
Small grains
Fine feeling

3. What is an Igneous Rock?
Forms from the cooling of magma or lava.

4. Classifying Igneous Rocks
Origin
Texture
Mineral Composition

5. Origin: Intrusive vs. Extrusive
Igneous rock that formed when magma hardened beneath Earth’s surface.
Extrusive
Igneous rock that formed from lava that erupted onto Earth’s surface.

6. Texture of Igneous Rocks
Depends on…
Size and shape of mineral crystals.
Large grains
Coarse feeling
Small grains
Fine feeling

7. Texture of Igneous Rocks
Rapidly Cooling = Extrusive
Forms fine-grained igneous rocks with small crystals
Slowly Cooling= Intrusive
Forms coarse-grained igneous rocks with varied sizes of crystals.

8. Extrusive
Rapidly cooling lava that erupted onto Earth’s surface.
Rapidly cooling = fine-grained crystals.
Obsidian

9. Intrusive Slow cooling magma that hardens beneath Earth’s surface.
Slow cooling = large, coarse-grained crystals that vary in size and shape.
Porphyry

10. How Do Geologists Determine Mineral Composition?
Crystal shape and size
Magnet test- to see if it contains magnetic metals.
Acid test to see if the rock includes minerals that contain compounds called carbonates.