1. 4-2 Igneous Rocks
forms when molten/melted rock (magma or lava) cools and hardens (solidifies)

2. “How do igneous rocks form?”
Examine samples of granite and obsidian
What is the texture of each?
Coarse, fine, glassy
Which one is NOT made of crystals?
Both are igneous rocks, made of similar minerals. What can you infer about how/where each were formed?
Granite
Obsidian

3. Igneous Rocks probably first rocks on Earth ignis means “fire”
think of “ignite”

4. Label the lava and magma

5. PERFORMANCE TASK 2 CAN BE COMPLETED NOW!!

6. Two Types of igneous rocks
2. Intrusive
from magma (coarse-grained)—cool slowly
ex: granite
most abundant igneous rock
makes up much of continental crust
forms core of many mountain ranges
1. Extrusive
from lava (fine-grained)—cool quickly
ex: basalt
most common extrusive igneous rock
especially common in oceanic crust

7. {enrich} Igneous rock--mineral composition
Mafic
forms dark-colored rocks
lots of calcium, iron, and magnesium (low in silicon)
ex: basalt
Felsic
forms light-colored rocks
less dense
lots of aluminum, potassium, silicon, and sodium
ex: granite

8. Make a Double Bubble or a Venn Diagram
Basalt compared to Granite (see Brainpop)
Include: intrusive/extrusive, coarse/fine grained, minerals that make it up, color, dark or light-colored, and silica content
see handout for help

10. Questions: What is the most common igneous rock? granite
Why does PUMICE float in water?
It came from an explosive volcano, so it had a lot of trapped air bubbles (so density less than 1)
Why does lava cool more quickly than magma?
exposed to the air or water

11. Questions: What determines the texture of an igneous rock?
>>how fast the lava/magma cools (and if the volcano is explosive)
A batholith forms from a large magma chamber that slowly cools deep beneath the earth’s surface. What type of texture is this igneous rock formation most likely to have?
>>coarse-grained

12. PERFORMANCE TASK #3