Rocks How Rocks Form Section 6.1
While You Read • Igneous Rocks: formed by cooling and hardening of magma. • Sedimentary Rocks: formed when sediment compacts and cements together. • Metamorphic Rocks: formed when heat and pressure change other rocks.
6.1 After You Read List as many natural forces contributing to the rock cycle as you can. Heat/pressure; melting, Solidification from cooling; weathering and erosion; burial and compaction
6.1 After You Read Explain why the rock cycle is complex and variable. Give an example. The rock cycle can take many shortcuts past some steps or can retrace steps. For example, a sedimentary rock may melt directly into magma without passing through a metamorphic stage.
6.2 Igneous Rocks • felsic • mafic • underground • granite • gabbro • diorite
6.2 After You Read Choose a mineral discussed in the section. Use the organizer you made while reading to classify the mineral. Describe the mineral’s chemical and physical properties. Basalt is a mafic rock. It hardens at the surface from lava flows. Basalt is fine-grained and belongs to the gabbro family.
6.3 After You Read 1. List and describe the three types of clastic sedimentary rocks. • Conglomerate rocks are made of large fragments loosely bound into a coarse rock. • Sandstone rocks are made of small quartz sand grains, with a lot of air space around them. • Shale rocks are made of tiny fragments of densly packed clay minerals.
6.3 After You Read 2. Explain the origin of nodules, concretions, and geodes. Nodules and concretions result when minerals gather around a fragment or other impurity. Geodes may form when minerals concentrate in cavities left by groundwater.
6.4 Metamorphic RocksWhile You Read 1. Metamorphic process: Rock’s characteristics are changed by heat and pressure from Earth’s internal layers, the weight of other rocks, or rock deformation during mountain building.
6.4 Metamorphic RocksWhile You Read 2. Local metamorphism occurs in small, distinct areas. 3. Hot magma heats and changes existing rock coming in contact with it. 4. Deformations occur as high pressure from stress of friction changes the shape of rocks.
6.4 Metamorphic RocksWhile You Read 5. Regional metamorphism occurs as large areas change when pressure of mountain building compacts rocks and pushes them toward hotter inner Earth layers.
6.4 After You Read • Name the factors that contribute to metamorphism and describe how they can interact to form different metamorphic rocks. Factors are heat, pressure, fluids or gases the rocks contacts, and dryness of parent rock. They can combine in many ways, resulting in different changes to parent rocks, and thus different metamorphic rocks result.
6.4 After You Read 2. Explain why some metamorphic rocks foliate while others do not. Rocks made of densely packed and uniform crystals tend to not foliate while those made in layers or bands tend to foliate.