Rock Types Three Main Types of Rocks: Igneous Sedimentary Metamorphic
Igneous Rocks Formed from magma (molten rock below earth’s surface) or lava (molten rock above earth’s surface). When molten rock crystallizes (cools/hardens), Two types of Igneous Rocks can Form: Intrusive: cool slowly inside earth’s crust allowing for large crystals to grow Extrusive: cool quickly above earth’s surface not allowing for any crystals to grow or allowing for very small crystals to grow Examples include: Granite and gabbro (intrusive) and basalt and obsidian (extrusive)
Sedimentary Rocks Formed from pieces of other rocks (sand, shells, pebbles etc…) i.e. sediment that gets glued and compacted together. Different Types Include: Clastic – made from other pieces Examples sandstone, conglomerate, shale Chemical – precipitates or evaporates Example rock salt (halite) Organic – formed from once living things Examples coal, limestone Fossils are found in sedimentary rocks.
Metamorphic Rocks Formed from intense heat and pressure. Two Types: Foliated: ribbonlike/banded layers Examples slate, phyllite, schist, gneiss Non-foliated: crystals (no banding) Examples quartzite, marble May have shiny crystals as well as the minerals in the rock change due to the intense heat and pressure.
Key Identifying Characteristics Igneous Rocks: Gas bubbles holes created from trapped gas Glassy surface shiny smooth surface from quick cooling rocks Crystals small, flat surfaces that are shiny or sparkly Sedimentary Rocks: Sand or pebbles individual stones, pebbles, or sand grains visible in the rock FossilsI imprints of shells, insects, leaves etc… Metamorphic Rocks: Ribbonlike layers wavy or straight stripes/bands of different colors in the rock
How Rocks Change Rocks change due to various processes. Processes Include: Heat and Pressure Melting and Cooling Weathering and Erosion Compacting and Cementing
Heat and Pressure Heat from the earth’s interior can melt rock and pressure from overlying rock can also morph (change) rocks from one type to another. Heat increases dramatically the deeper a rock gets pulled under the earth’s surface – prior to melting a rock can change chemically to become another rock. Pressure from overlying rock also can change a rock chemically into another type of rock. Heat and pressure work together and this is known as metamorphism thus creating metamorphic rocks.
Melting and Cooling Melting: Temperatures between 600 and 1300 degrees Celsius (1100 – 2400 degrees Fahrenheit) melt rock and turn it into magma Cooling: any rock that forms from cooling magma is an igneous rock Two Types of Igneous Rock: Intrusive form from slowly cooling magma inside earth Extrusive form from quickly cooling lava above/on earth’s crust
Weathering and Erosion Weathering: the breaking apart or wearing down of rock due to water, wind, gravity, temperatures, and other elements at the earth’s surface. Creates sediments. Erosion: Transportation of weathered material via water, wind, or gravity.
Compacting and Cementing Compacting: Sediment formed from weathering and erosion accumulates (is deposited/left behind) in oceans, lakes, and valleys this allows for layers of sediment to build up Each layer presses down on the layer below it, thus compacting (pushing down on) bottom layers. Cementing: When water passes through spaces in between particles of sediment this helps cement the particles together forming sedimentary rock
The Rock Cycle James Hutton (1726-1797) is attributed with the concept of the rock cycle. Main Idea of Rock Cycle: Rocks are continually changing from one type to another and back again Elements that make up rock aren’t destroyed or created, they are just being recycled
Click and Explore the Rock Cycle by Rolling Your Mouse Over It