OVERVIEW

This is the first chapter of Part II which deals with the systems and cycles of the solid earth. This chapter discusses the basic materials of the solid earth - rock and minerals - and some principals of their formation. These are linked to the cycle of rock change which describes how different rock types develop as earth materials are cycled and recycled through geologic time.

• The elements oxygen and silicon account for about 75% of the earth's crust, while the metallic elements iron, aluminum and the base elements account for most of the rest.
• The elements of the crust are combined in inorganic chemical compounds called minerals.
• These minerals are mixed together in various proportions to form many kinds of rock.
• The rocks of the earth's crust are grouped into three major classes: igneous, sedimentary and metamorphic rocks.
• Igneous rocks form when molten material from the earth's interior cools and solidifies in the crust.
• Magma cooled slowly below the surface forms coarse-textured intrusive igneous rocks. Lava cooled rapidly at the surface forms fine-textured extrusive igneous rocks.
• Igneous rocks consist mainly of silicate minerals containing silicon, oxygen and metallic elements. The kind of metallic elements present determines the mineral density.
• Less dense felsic minerals dominate the igneous rocks of the upper crust while more dense mafic and ultramafic minerals dominate those of the lower crust.
• Silicate minerals undergo chemical changes called mineral alteration when exposed to air and water at the earth's surface.
• Most clay minerals are produced by mineral alteration.
• Weathering, or the breakdown of rocks into smaller particles known collectively as sediment, occurs through both mineral alteration and physical disintegration.
• Layers of mineral sediment and organic matter accumulate in oceans and low-lying land areas to be compacted and hardened into sedimentary rocks. Different types of sediment produce different kinds of sedimentary rock.
• Igneous and sedimentary rocks can be altered by heat and pressure to form metamorphic rocks.
• The cycle of rock change describes the circulation of rock material between the earth's interior and the crust. This is a very slow process powered by the heat of radioactive decay deep within the earth.

KEY TERMS

mineral            felsic             lava               
rock               mafic              magma              
igneous rocks      extrusive igneous  andesite           
sedimentary rocks  rock               basalt             
metamorphic rocks  intrusive igneous  granite            
quartz             rock               pluton             
                   mineral                               
                   alteration                            
                   cycle of rock                         
                   change                                

STUDY QUESTIONS

1. What is the earth's crust and what are its major chemical constituents?
2. What is the difference between a mineral and a rock?
3. How does the rate at which molten material cools affect the character of the resulting igneous rock?
4. Define silicate mineral. Distinguish between the felsic, mafic and ultramafic types and give an example of each.
5. Name two igneous rocks that have the same mineral composition but a different texture.
6. List and describe the major chemical processes by which silicate minerals are altered when they are exposed to air and water at the earth's surface.
7. How are most clay minerals formed?
8. What are the three main classes of sedimentary rocks?
9. What is the process of chemical precipitation and how can this contribute to the formation of sedimentary rocks?
10. Hydrocarbon compounds are found in some sedimentary rocks. How are they formed?
11. What are metamorphic rocks? Name three metamorphic rocks and describe how they are formed.
12. Sketch a diagram of the cycle of rock change. Show the main flow pathways, the kinds of rocks formed within the cycle and the power sources for the cycle.
13. Temperature change with depth below the earth's surface is different beneath the oceans than beneath the continents. Sketch a graph to show how it differs. Explain why this difference exists.