Grade Level: 4th-8th grades Subject Area: Earth Science Objectives: Introduce students to the rock cycle. Students will have an opportunity to categorize rocks from the three rock types. Students investigate the rock cycle and experiment with changing materials from type to another. method: With hands on experience the students will have a better understanding of the characteristics of the three types of rocks and with the changes that take place in the rock cycle. background: Rocks are composed of one or more minerals. Minerals are naturally occurring elements (gold) or inorganic compounds (quartz). Each mineral is a naturally occurring, inorganic solid with a specific crystal structure and chemical composition. There are three major categories of rocks: igneous, sedimentary, and metamorphic. Igneous rocks form from molten rock (magma) that has cooled. Examples are granite, basalt and pumice. Igneous rocks that cool slowly beneath the Earth s surface usually contain large interlocking crystals. Igneous rocks that are created in volcanic eruptions have smaller crystals or may be glassy in texture. Detrital or clastic sedimentary rocks form when sediments are deposited by water or wind on the surface of the earth, they are lithified over time, as the sediment grains are cemented together to form rock. Other sedimentary rocks form by chemical processes. Sedimentary rocks are commonly layered, a result of the way the sediments that make them up are deposited. Metamorphic rocks can begin as any rock type but they are altered (not melted) by heat, pressure and/or chemically active fluids. Some examples are: sandstone which metamorphoses into quartzite, limestone with metamorphoses into marble, and granite which metamorphoses into gneiss. Crystals commonly seen in metamorphic rocks are usually oriented in lines or sheets called foliation. Weathering, erosion and mass wasting are acting on Earth materials at or near the Earth s surface at all times. As they do they transform rock into sediment, crumble mountain ranges, fill lakes and streams with sediments and continuously change the landscapes around us. Weathering and erosion are two different processes. Weathering refers to the physical and chemical breakdown of Earth materials at or near the surface. Erosion refers to the physical removal of Earth materials by water, wind or ice. 1
materials: There are two main types of weathering: mechanical and chemical. Mechanical weathering processes act to break Earth materials into smaller pieces. Examples of mechanical weathering include: frost wedging, unloading, thermal expansion and some biological activity. Chemical weathering involves chemical reactions that convert Earth materials to one or more new compounds. Examples of chemical weathering processes include: dissolution, oxidation and hydrolysis. Sample of igneous, sedimentary and metamorphic rocks Or pictures of each type of rock shown on page 3 Rock Cycle diagram Sugar cubes Granulated sugar Mortar & Pestle or other device to crush sugar cubes Container to melt sugar grains in Hot plate or heating device String or popsicle stick Procedure: Part 1 Categorizing rocks by major rock type 1. Introduce the rocks using the following information and the pictures below or hand samples of the rocks. Igneous rocks are formed from rocks that melted deep within the Earth. These melted rocks are called magma. As magma is pushed up toward the surface of the Earth, it begins to cool. Different igneous rocks are formed depending on the presence of different minerals and how fast the magma cools. Some igneous rocks include pumice, granite, obsidian and basalt. The rapid cooling of lava that is erupted from a volcano can produce pumice, a rock with a large volume of air spaces in it, similar to a sponge. The rapid cooling of lava can also produce obsidian and fine-grained igneous rocks such as basalt, andesite and rhyolite. Slower cooling produces larger crystals and rocks such as granite, gabbro and diorite. 2
Some sedimentary rocks are formed through the weathering, erosion, transportation, deposition and lithification of sediments. Sediment consists of sand, mud, bodies of animals, shells, gravel and other materials. Over long periods of time, these sediments can be covered by other particles and layers are pressed down by the weight of sediments and water above. Gradually, the sediments are lithified into sedimentary rock. Geologists can determine the age of a sedimentary rock by its thickness, and mineral layers, and the plant and animal remains it may contain. Nearly 75 percent of the land area of the Earth is covered with sedimentary rocks. Limestone, shale, sandstone, breccia and conglomerate are some examples. Part 2 Investigating the rock cycle 1. Give each group several sugar cubes. Ask students to make observations of the sugar cube. 2. Ask students which major rock type the sugar cubes share the most characteristics with. They should note that sugar grains are like grains of sediment and that the sugar grains are cemented together like sand grains in sandstone (sedimentary rock). 3. Ask students to crush the sugar cubes. Metamorphic rocks are formed from igneous, sedimentary, or other metamorphic rocks. They are rocks that have been changed by heat, pressure, or chemically active fluids. Heat and pressure inside the Earth can cause minerals in rocks to change. Examples of metamorphic rocks are marble, gneiss, schist, some types of coal and slate. Many metamorphic rocks show foliation. Foliation is the alignment of mineral grains within the rock. Foliation forms when pressure is applied to rocks with mineral grains that are long and thin or flat and platy. The mineral grains line up with each other. 2. Split the students into two (or more) teams. 3. Give each team a set of pictures or hand samples of rocks. Ask the students to spread them out so everyone on the team can see them. 4. The teacher should have three cards. One for each of the main rock types: IGNEOUS, SEDIMENTARY, METAMORPHIC. The teacher holds up one of the cards. Students on each team organize their pictures/ rock samples and separate out the ones that match the rock type the teacher is holding up. 5. Award each team points for their correct answers. 3
4. Help students understand that this is similar to mechanical weathering. The sugar cubes are broken own mechanically into much smaller grains. 5. Pour the broken down sugar cube grains into a container that can be heated. Tell students that moving the grains from one place to another is like erosion. 6. Heat the sugar grains slightly until they just begin to stick together (but DO NOT melt). Applying heat, but not melting the sugar is like metamorphosis. You might give students the example of a magma chamber from a nearby volcano heating up rocks surrounding it and metamorphosing them. 7. Return the sugar to the heat. Continue to heat until all of the sugar grains melt. The melted sugar grains represent magma. 8. Allow the melt to cool and crystallize without disturbing it. This will take several minutes. This process simulates the crystallization of igneous rock. 9. Remove the cooled sugar from the container. Break into small pieces (again simulating weathering). 10. Extension activity to simulate creating a sedimentary rock from a solution: add additional sugar so that the ratio is about 1 cup of sugar to ½ cup of water. Heat in a container until all of the sugar dissolves and the solution just comes to a boil. Place a string or popsicle stick in the solution and allow to stand for several days. Sugar crystals (rock candy) will grow on the string/stick from the solution. Discussion: Ask students what is happening at each step in the activity. Relate the steps to the rock cycle. At the conclusion of the activity show students the rock cycle diagram or give them a copy. Ask them to write what they observed for each step in the process. Emphasize that rocks continue to change and that each type of rock and each step in the cycle is an important step in the rock cycle and the everchanging Earth. Ask students to volunteer thoughts about how the changes in rocks and the Earth affect them and their community. 4
Extension activities: Use the rock cycle diagram to help students organize an investigation to identify regions around the globe where each of the processes shown in the rock cycle are presently occurring. Students could use Google Earth to create a tour around the globe showing the different locations. Have students research Sunset Crater in Arizona. This location shows recent volcanic activity. Students could consider the geology of the area, relate it to the Grand Staircase region and add in information about local indigenous peoples living in the area when Sunset Crater was active. references: Rock Cycle Diagram http://www.geolsoc.org.uk/gsl/ education/rockcycle/page3446.html Igneous rock images http://geology.csupomona.edu/alert/ igneous/texture.htm Sedimentary rock images http://facweb.bhc.edu/academics/ science/harwoodr/geol101/labs/ Sediment/ Metamorphic rock images http://geology.csupomona.edu/alert/ metamorphic/metarxs.htm Mechanical weathering diagram http://www.berkeleycitycollege.edu/ faculty/rhaberlin/images/mwmech.gif Contact metamorphism diagram http://volcano.oregonstate.edu/ vwdocs/vwlessons/lessons/metrocks/ Picture4.gif The National Park Foundation is the national charitable partner of the National Park Service. 5