1 How Rocks Form

1. You Rock! Well… at least the Earth Rocks! 1How Rocks Form 2Igneous Rocks 3Sedimentary Rocks 4Metamorphic Rocks

2. How Rocks Form VOCABULARY In general, a rock is a group of minerals bound together. rock igneous Igneous, sedimentary, and metamorphic rocks are formed, broken down, and reformed in a recurring process called the rock cycle. magma sedimentary sediment metamorphic rock cycle click image to enlarge

3. 6.2Igneous Rock Granite is igneous rock formed from felsic magma. Basalt is igneous rock formed from mafic magma. VOCABULARY Igneous rocks form as molten rock solidifies, as magma deep in the crust or lava at Earth’s surface cool. felsic mafic pluton Felsic magmas form light-colored, silica-rich rocks. Mafic magmas form dark-colored rocks rich in iron and magnesiums. batholith Igneous rock texture depends mainly on the rate at which magma or lava cools.

4. 6.2Igneous Rock Chemical Composition Texture coarse- grained fine- grained glassy porous felsic granite rhyolite obsidian most pumice felsic- intermediate granodiorite intermediate diorite andesite basalt glass mafic gabbro basalt scoria peridotite, dunite, pyroxenite ultramafic VOCABULARY Igneous rocks are grouped into families by mineral composition and texture. felsic mafic pluton batholith diabase

5. 6.2Igneous Rock Volcanic neck Laccolith Volcano Stock Dike Sill VOCABULARY Magma that solidifies underground forms various types of igneous intrusions. felsic mafic pluton batholith Batholith

6. Sedimentary Rock VOCABULARY Sedimentary rocks form from sediments that result from weathering and erosion of rock at Earth’s surface. They often occur in layers, formed over time as different sediments are deposited on top of each other. cementation stratification fossil

7. Sedimentary Rock Clastic: Sandstone Chemical: Rock Salt Flat Organic: Limestone Cliffs VOCABULARY Sedimentary rocks are grouped by the type of sediment from which they form: clastic, chemical, or organic. cementation stratification fossil

8. 6.3Sedimentary Rock Sands and Gravels Silt and Clay Sands Conglomerate Sandstone Shale VOCABULARY Clastic sediments are often sorted by water action before pressure and mineral cements turn them into rock. cementation stratification fossil 1. A river moves sediment into a lake. 2. Particles are sorted by size. The largest gravels are the first to be deposited, followed by sands, and then silt and clay. 3. Over time, the sediments are buried, compacted, and may be cemented.

9. Sedimentary Rock VOCABULARY Clastic sediments are often sorted by water action before pressure and mineral cements turn them into rock. cementation stratification fossil Fossils, ripple marks, mud cracks, nodules, concretions, and geodes features associated with sedimentary rocks.

10. 6.4Metamorphic Rock becomes becomes Shale Slate becomes Phyllite Schist VOCABULARY Metamorphic rocks form when heat or pressure or both alter parent, or preexisting, rocks. parent rock metamorphism deform

11. 6.4Metamorphic Rock VOCABULARY Metamorphic rocks form when heat or pressure or both alter parent, or preexisting, rocks. parent rock metamorphism deform Metamorphism can occur across a region, as in mountain building events, or it can occur in smaller local areas. A metamorphic rock may be described and identified according to its parent rock, mineral composition, and texture.