ROCK CYCLE LESSON
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Students should read the passage
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What are rocks? Rocks are solid, natural elements made of minerals and other materials. Rocks can be as small as a pebble or as large as a canyon wall. Some rocks are smooth, while others are very rough.
Thick layers of rock make up the earth. Scientists group rocks by how they form. The three main types of rock are igneous, sedimentary, and metamorphic.
Igneous rock forms in the mantle below earth's surface. Heat beneath the surface melts rock. The melted rock then mixes with hot gases to form magma. Magma changes into igneous rock when it cools. Igneous rocks that form below earth's crust are called intrusive rocks. Igneous rocks that form outside on earth's surface are called extrusive rocks. Intrusive rocks form when hot magma fills cracks in earth's crust. Mineral crystals form as the magma cools. Diamonds and quartz are some minerals that form in intrusive rock. Rock that forms from quickly cooled lava, such as rhyolite, has small mineral grains. Rocks that form from slowly cooled magma, such as granite, have large mineral grains.
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