CHAPTER 13 Focus Points
13.1 Minerals and Rocks: Building Earth’s Crust
Composition of rocks: Almost all rocks are composed of one or more minerals.
Rock families: All rocks can be grouped into the igneous, sedimentary, and metamorphic rock families.
The rock cycle: Rocks are formed, transformed, and recycled into the mantle through the rock cycle.
13.2 Cooling the Inferno: Igneous Rocks
Melting: Mantle material melts into magma by means of decompression melting and flux melting.
Tectonic settings: Igneous rocks form in hot spots, mid-
Intrusive igneous rocks: Intrusive igneous rocks cool slowly, allowing time for the growth of crystals.
Extrusive igneous rocks: Extrusive igneous rocks cool relatively quickly and have smaller or no crystals.
13.3 Layers of Time: Sedimentary Rocks
Prevalence of sedimentary rocks: Sedimentary rocks cover 75% of the crust’s surface, but they make up only 4% of the crust.
Sedimentary rock types: The three types of sedimentary rocks are clastic, organic, and chemical sedimentary rocks.
Coal: Coal is widely used as an energy source, but its mining can cause environmental problems.
Evaporites: Evaporites are an economically important type of chemical sedimentary rock.
Sedimentary rocks and Earth history: Fossils in sedimentary rock reveal ancient life and ancient environments on Earth.
13.4 Pressure and Heat: Metamorphic Rocks
Metamorphism: Rock of any type can experience metamorphism if it is heated, subjected to high pressures, or both.
Tectonic settings of metamorphism: Most metamorphism occurs at convergent plate boundaries.
13.5 Geographic Perspectives: Fracking for Shale Gas
Fracking and fuel supply: In 2000, shale gas provided about 1% of the U.S. natural gas supply. This number is expected to rise to 50% by 2035.
Pros and cons: The hydraulic fracturing (fracking) technique of extracting natural gas from shale has both positive and negative results.