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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, sedimentary rocks typically have grains that one can see, whereas igneous rocks don’t. Crystals in metamorphic rocks are often arranged in bands.
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There are three main categories of rocks, which are defined by how the rocks are formed.
Sedimentary Rocks
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. Some samples of sedimentary rocks include limestone, sandstone, coal and shale.
Igneous Rocks
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. Look for crystals in igneous rocks. Examples of igneous rocks are gabbro, granite, pumice and obsidian.
Metamorphic Rocks
Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. One way to tell if a rock sample is metamorphic is to see if the crystals within it are arranged in bands. Examples of metamorphic rocks are marble, schist, gneiss, and slate.
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