1. Igneous Rocks

2. How are igneous rocks formed?
Key Concept #1
How are igneous rocks formed?
the melting and
solidification of
magma

3. How to Tell Igneous Rocks
The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that:
•Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks.
•They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale.
•Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals).
How to Tell Igneous Rocks
The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that:
•Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks.
•They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale.
•Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals).
How to Tell Igneous Rocks
The key concept about all igneous rocks is that they were once hot enough to melt. The following traits are all related to that:
•Because their mineral grains grew together tightly as the melt cooled, they are relatively strong rocks.
•They're made of primary minerals that are mostly black, white or gray. Any other colors they may have are pale.
•Their textures generally look like something that was baked in an oven. The even texture of coarse-grained granite is familiar from building stones or kitchen counters. Fine-grained lava may look like black bread (including gas bubbles) or dark peanut brittle (including larger crystals).

4. Name four places where igneous rocks form
Igneous Rocks: Key Concept #2
Name four places where igneous rocks form

5. Volcanoes
Rifts/Ridges

6. Igneous rocks form at four main places on Earth:
•At divergent boundaries, like mid-ocean ridges, plates rift apart and form gaps that are filled by magma.
•Subduction zones occur whenever a dense oceanic plate is subducted underneath another oceanic or continental plate. Water from the descending oceanic crust lowers the melting point of the above mantle, forming magma that rises to the surface and forms volcanoes.
•At continental-continental convergent boundaries, large landmasses collide, thickening and heating the crust to melting.
•Hot spots, like Hawaii, form as the crust moves over a thermal plume rising from deep in the Earth. Hot spots form extrusive igneous rocks.

7. What determines crystal size?
Igneous Rocks: Key Concept #3
What determines crystal size?

8. cooling time

9. crystal size
cooling time

10. Large Crystals Indicate
long cooling time
Small Crystals Indicate
short cooling time

11. What’s the difference between extrusive and intrusive igneous rocks?
Igneous Rocks: Key Concept #4
What’s the difference between
extrusive and intrusive igneous rocks?

12. Intrusive
Extrusive
form on or near the
surface
(small crystals)
form below the
surface
(large crystals)

13. Igneous Rocks: Key Concept #5
Characteristics used to classify igneous rocks

14. Key Concept #5 texture glassy } extrusive fine
Characteristics used to classify igneous rocks
texture
glassy }
extrusive
fine

15. Key Concept #5 texture coarse } intrusive very coarse
Characteristics used to classify igneous rocks
texture
coarse }
intrusive
very coarse

16. Key Concept #5 color dark light
Characteristics used to classify igneous rocks
color
dark
light

17. low high Key Concept #5 density
Characteristics used to classify igneous rocks
density
low
high

18. Key Concept #5 composition mafic contains Fe and Mg felsic contains Al
Characteristics used to classify igneous rocks
composition
mafic
contains Fe and Mg
felsic
contains Al

19. Key Identifying Features of Igneous Rocks
Igneous Rocks: Key Concept #6
Key Identifying Features of Igneous Rocks

20. the grains have been melted and are now physically connected
Glassy Texture
usually black in color
Interlocked Grains
the grains have been melted
and are now physically connected

21. Igneous Rocks as Resources