1. Igneous Rocks

2. Igneous Rocks I. Formation of Igneous Rocks
Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface.
Obvious crystals/mineral grains.
Takes a long time to form.
2. Extrusive igneous rocks are formed when lava hardens above Earth’s surface.
No obvious crystals.
Takes a relatively short amount of time.

3. Igneous Rocks II. Classification of Igneous Rocks
Igneous rocks can be classified based on their: texture and composition.
1. Textures
• Coarse-grained texture is caused by slow cooling resulting in larger crystals.
• Fine-grained texture is caused by rapid cooling resulting in smaller, microscopic mineral grains.

4. Igneous Rocks Texture (continued)
• Glassy texture is caused by extremely rapid cooling.
Porphyritic texture is caused by slow then rapid cooling. You will see a fine-grained texture with larger crystals within the rock.
Vesicular – a texture that has lots of vesicles (holes) from escaping gas.

5. Course-Grained Igneous Texture
Obvious crystals

6. Fine-Grained Igneous Texture
No obvious crystals

7. Obsidian Exhibits a Glassy Texture.
Extremely rapid
cooling
No crystals

8. Both fine and coarse-grained = porphyritic
porphyritic texture
Fine-grained with some crystals

9. Both fine and coarse-grained = porphyritic
vesicular texture
Lots of vesicles (holes) from gas

10. Igneous Rocks 2. Composition - What the rock is made of
• Granitic composition rocks are made mostly of light-colored minerals like quartz and feldspar.
• Basaltic composition rocks are made mostly of dark-colored silicate minerals like pyroxene.

11. Igneous Rocks b. Composition (continued)
• Andesitic composition rocks are between granitic light-color minerals and basaltic composition dark-colored minerals.
• Ultramafic composition rocks are made mostly from dark and heavy minerals like olivine.

12. Classification of Igneous Rocks

13. Classification of Igneous Rocks
TEXTURE DESCRIPTIONS

14. Classification of Igneous Rocks
WHAT ROCK LOOKS LIKE

15. Classification of Igneous Rocks
HOW LIGHT OR DARK THE ROCK IS

16. Classification of Igneous Rocks
NAME OF ROCK

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18. Add these notes to your TOC
Igneous Rocks Classification

19. At lab today: Look at rock samples- Sketch and color/shade each rock
make/ write observations about each rock in the table
Such as: texture, composition (colors), determine type of igneous rock (intrusive, extrusive); record if there are vesicles, etc
Name the rock
Add a row for Glassy Texture

20. Period 2 Lab 1 – Jam, Aiden H, Ari Lab 2 – Delaney, Sophia
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