1. Chapter 6 – Rocks Section 6.1 – Rocks and the Rock Cycle

2. Section Objectives
Identify the 3 major types of rock, and explain how each type forms.
Summarize the steps in the rock cycle.
Explain Bowen’s reaction series.
Summarize the factors that affect the stability of rocks.

3. Rocks Are: The materials that make up the solid part of the earth.
A collection of one or more minerals, may not be crystals (glass).

4. 3 Major Types of Rocks (based by the way the rocks form)

5. Igneous Rock (Latin: “from fire”)
Forms when molten rock (magma) cools and hardens.
Magma is called lava when it is erupted on the Earth’s surface.

6. Satellite Photograph;
Sediments
Agents of erosion (wind, water, ice, gravity) break down all types of rock into small fragments.
These fragments of rocks, crystals, and organic matter are known as sediment.
Satellite Photograph;
Rio Tinto, Spain

7. Sediments Deposited
Sediments are carried away and deposited in another area by wind, water, and ice. They are then compressed and/or cemented together to harden into……..

8. Sedimentary Rocks

9. Pressure, Heat, and Chemical Processes
Can change the form of an existing type of rock. The result is an altered rock known as………

10. Metamorphic Rock
Greek: “changed form”

11. The Rock Cycle
Any rock can be changed into another of the three types of rock.
Rock cycle video

12. Changed Conditions = Changed Rock
A particular body of rock does not always pass through each stage of the rock cycle.

13. Properties of Rocks
The physical characteristics of rock reflect the chemical composition of the rock

14. N. L. Bowen (1928)
Proposed that different minerals form at different times during the cooling of magma, and that they generally form in the same order. The pattern of mineral formation depends on the chemical composition of the magma.

15. Bowen’s Reaction Series
Minerals form in one of two ways. The first (right-hand side) is a gradual, continuous formation of plagioclase minerals that have similar chemical compositions.
Zoned Plagioclase:
Ca rich core, Na rich rim

16. The Second Way
Sudden changes in mineral types, the discontinuous reaction series of Fe-Mg minerals (the left-hand side of the diagram).

17. Chemical Stability of Minerals
The rate at which a mineral breaks down is dependent on the chemical stability of the mineral, and is a measure of the tendency to maintain its original composition rather than break down to form a different chemical.

18. Depends on Chemical Bond Strength
Generally, the most resistant minerals have the highest number of bonds between silica and oxygen. This reflects Bowen’s reaction series (first formed, first destroyed).

19. Physical Stability of Rocks
Rocks have natural zones of weakness that are determined by how and where the rocks form. Once the surfaces of these weaknesses are exposed to air and water, chemical and physical weathering begins.

20. Sedimentary rock video
Sedimentary Rocks
Zones of weakness along layers or through fractures that develop when pressure is released when the rock is uplifted to the Earth’s surface.
Sedimentary rock video

21. Metamorphic Rock video
Metamorphic Rocks
Can have layering also, which are zones of weakness.
Metamorphic Rock video

22. Igneous Rocks
Can have evenly spaced zones of weakness, called joints, that form as the rock cools and contracts.
Igneous rock video

23. Assignment Significant Digits 6.1 Key Terms
Rock Cycle Directed Reading
Anguish