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Give each group a copy of the Word Sunburst handout on Rocks and ask them to write one-word observations about their rocks. When they finish, give students another index card and a marker and ask each to write one observation from their Sunburst (using big printing) on the card. Make a whole class Sunburst out of flipchart paper, with the word ROCK in the center. Ask each student to come up and tape a “rock word” to the rays of the Sunburst (hard, shiny, gray, black, pointy, crystals, rough, sandy, sharp, etc.) When everyone is finished, ask students what they now know about rocks that they didn’t know before. Also ask them what questions they now have about rocks that they hadn’t thought of before the investigation. Write these down for later.
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Complete this investigation by asking your students to reflect on this question and how their answers may have changed as a result of this investigation. For example, most rocks are pretty hard and are solid, but they are different in color, texture, size, shape and shininess.
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There are three main categories of rocks, which are defined by how the rocks are formed.
Sedimentary Rocks
Sedimentary rocks are formed from sediment, which is solid, loose pieces of rocks (in the form of sand, silt, clay, and gravel), or the remains of living things found at the surface of the Earth. Sediment is material that has been eroded and deposited by wind, running water, waves, and ice. Sediment can also form from material left behind by the evaporation of seawater, or the settling of the remains of animals and plants in oceans, lakes, and swamps. In certain conditions, and over a very long period of time, sediment can become compacted and cemented into sedimentary rock. Sedimentary rock is often found in layers. One way to tell if a rock sample is sedimentary is to see if it is made from grains.
Igneous Rocks
Rocks are mixtures of one or more minerals. Just like the apples, butter, flour, and sugar are the ingredients of apple pie, minerals like quartz, mica, and feldspar are the ingredients of an igneous (from the Latin word for fire) rock called granite. Igneous rocks come from melted rock material, or magma, that lies under Earth’s surface. Igneous rocks form when magma from inside the Earth moves toward the surface, or is forced above the Earth’s surface as lava and ash by a volcano. Here it cools and crystallizes into rock.
Metamorphic Rocks
Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. In the very hot and pressured conditions deep inside the Earth’s crust, both sedimentary and igneous rocks can be changed into metamorphic rock. In certain conditions these rocks cool and crystallize, usually into bands of crystals. Later they can become exposed on Earth’s surface. One way to tell if a rock sample is metamorphic is to see if the crystals within it are arranged in bands.
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