1. Igneous Rocks

2. BIG Idea
Igneous rocks were the first rocks to form as Earth cooled from a molten mass to the crystalline rocks of the early crust.

3. The word ‘Igneous’ means:
of or like fire [Latin ignis fire]

4. What are igneous rocks?

5. IGNEOUS rocks are…
rocks that form when molten material cools and hardens either below or on Earth’s surface.

7. How do we define MOLTEN? melted changed into liquid form by heat
glowing ‘red-hot’

8. MAGMA: THE PARENT TO ALL ROCKS
Molten rock beneath the surface of the Earth (forms underground)

9. LAVA: molten rock that flows out ON to Earth’s surface

10. Igneous rocks are classified based on:
mineral composition
crystal size
texture

11. Two (2) Types of Igneous Rocks:
EXTRUSIVE: RAPID (fast) COOLING LAVA ON THE EARTH’S SURFACE
small or no crystals
fine-grained or glassy textures
INTRUSIVE: SLOW COOLING MAGMA DEEP WITHIN THE EARTH’S CRUST
larger crystals
coarser texture

12. TEXTURE What is the ‘texture’ of an igneous rock?
the size, shape, and arrangement of the crystals

13. 1. EXTRUSIVE: SMALL (or no) CRYSTALS - FINE GRAIN (fast cooling, no time to grow)

14. EXTRUSIVE rocks can have air pockets due to fast cooling…
Can you name this rock?
Hints:
it’s the only rock that will float on water, and
it’s used for pedicures…

15. Pumice!

16. This texture is described as ‘vesicular’
Gas pockets (holes) make the rock look ‘spongy’
pumice
vesicular basalt

17. scoria

18. Obsidian: cooled too quickly for crystals to form
Also known as ‘volcanic glass’

19. 2. INTRUSIVE: LARGE WELL-DEVELOPED CRYSTALS = COARSE GRAIN TEXTURE (slow cooling, a lot of time to grow)

21. PORPHYRITIC: LARGE AND SMALL CRYSTALS
Magma cooled in two stages

22. COMPOSITION OF IGNEOUS ROCKS
1. FELSIC:
high silica (Si and O) and aluminum (Al) content
light color
low density
Rhyolite

23. high iron (Fe) and magnesium (Mg) content
2. MAFIC:
high iron (Fe) and magnesium (Mg) content
dark color
high density
Basalt

24. 3. INTERMEDIATE:
medium color
medium density
Diorite

26. Lava Plateaus