1. Warm Up The three groups of rocks are classified by ____.
a. how they formed c. color
b. grain size d. chemical composition
Which of the following is true about rocks?
a. Rocks do not contain any nonmineral matter.
b. Rocks are composed of only one mineral.
c. Coal is not considered a true rock.
d. Most rocks are a mixture of minerals.
What type of rocks are formed by processes powered by the sun?
a. No rocks are formed by energy from the sun.
b. sedimentary rocks
c. igneous rocks
d. metamorphic rocks
Answers: 1) a. 2) d. 3) b.

2. Igneous Rocks
Chapter 3, Section 2

3. Formation of Igneous Rocks
Rocks that form when magma hardens beneath Earth’s surface are called intrusive igneous rocks
They have intruded into the existing rocks
As magma rises it cools, allowing elements to combine and form minerals, which combine to form igneous rocks
When lava hardens, the rocks that form are called extrusive igneous rocks
The have extruded onto the surface

4. Evolution of a Magma

5. Formation of Igneous Rocks
Intrusive - Granite
Extrusive - Rhyolite

6. Classification of Igneous Rocks
Texture and composition are two characteristics used to classify igneous rocks
Texture describes the appearance of an igneous rock based on its size, shape, and arrangement of interlocking crystals
Composition describes the proportions of light and dark minerals in the rock

7. Course/Fine-Grained Texture
If the magma cools slowly, it will have only have a few centers of crystal growth
Slow cooling results in the formation of large crystals (course-grained)
If magma or lava cools rapidly, a large number of tiny crystals compete for available ions
Rapid cooling of magma or lava results in rocks with small, interconnected mineral grains (fine-grained)

8. Course/Fine-Grained Texture
Course-Grained Gabbro
Fine-Grained Basalt

9. Glassy/Porphyritic Texture
Glassy Texture – solids produced so quickly that the ions are not able to align
Porphyritic Texture – rocks that have different size minerals, a result of different rates of cooling

10. Glassy/Porphyritic Texture
Glassy Texture - Obsidian
Porphyritic Texture - Andesite

11. Concept Check
How does the rate of cooling of magma or lava affect the texture of igneous rocks?
A slowly cooling magma or lava will produce rocks in which the mineral grains are relatively large. Quickly cooling molten material will result in rocks with small mineral grains. Lava that cools rapidly will produce a glassy rock. Rocks that form as a result of different cooling rates will have both large and small mineral grains.

12. Granitic/Basaltic Composition
Granitic Composition – Igneous rocks in which quartz and feldspar are the dominant minerals
Most granitic rocks also contain about 10% dark silicate minerals and 70% light silicate minerals
Basaltic Composition – rocks that contain many dark silicate minerals
Basaltic rocks are rich in iron and magnesium

13. Granitic/Basaltic Composition
Granitic Composition - Granite
Basaltic Composition - Gabbro

14. Other Compositional Groups
Andesitic Composition – rocks with a composition between granitic and basaltic
Andesitic rocks contain at least 25% dark silicate minerals
Ultramafic – rocks that are composed mostly of dark silicate minerals
Peridotite is an example of an ultramafic rock, although rare on the crust, it is thought that the mantle is made mostly of peridotite

15. Other Compositional Groups
Andesitic Composition - Andesite
Ultramafic - Peridotite

16. Bowen’s Reaction Series

17. Classification of Igneous Rocks

18. Concept Check
Describe the main differences between granitic and basaltic rocks?
Granitic rocks contain mostly quartz and feldspar and thus are light-colored. Basaltic rocks are rich in iron and thus are dark-colored and more dense.

19. Homework Read Chapter 3, Section 2 (pg. 70-74)
Do Chapter 3 Assessment #1-36 (pg )
For Section 2: Do #’s 5, 12-14, 23, & 35

20. Class Assignment Draw and Label the Rock Cycle. (p.67) Include:
Formation of Sedimentary rocks (5pts)
Weathering
Sediment
Formation of Igneous rocks (5pts)
Cooling Magma
Formation of Metamorphic rocks (5pts)
Heat & Pressure
Effort (5pts)