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Types of Rocks Use the Text to Answer Each Question Below Name Date Types of Rocks Use the text to answer each question below. 1. There are three types of rocks on Earth. Each rock type forms in a different way. Igneous rocks were the first rocks on Earth. They form from molten rock. Molten rock is rock that has turned to liquid because of extreme heat. Lava is the name for the molten rock that erupts from volcanoes. When molten rock is below the Earth’s surface, it’s called magma. When molten rock—either lava or magma—cools, it hardens into a solid. This forms igneous rocks. Some examples of igneous rocks are granite, obsidian and basalt. Much of Hawaii’s coast is covered in basalt. Waves break the basalt down over time, creating the black sand of some Hawaiian beaches. Which of the following is true about lava and magma? A. Lava and magma are both types of B. Magma uses waves to break down lava molten rock. over time. C. When magma cools and hardens it D. Lava is called magma when it’s below the becomes lava. Earth’s surface. 2. Sedimentary rocks begin forming when existing rocks are worn away by wind and rain in a process called weathering. Weathering breaks rock into smaller pieces called sediment. Erosion is the removal and movement of sediment. Weathering and erosion happen slowly, over thousands and even millions of years. Eventually, layers of sediment are deposited on top of one another and pressed together. Sedimentary rock is formed when sediment sticks together after liquid is squeezed out. Sometimes, fossils get trapped between sediment layers. The sediment of sedimentary rocks can range in size from a grain of sand to a shell or pebble. The name of the rock that’s created depends on the sediment that it’s made of. For example, shale is made of clay. Conglomerate is made of coarse sediment the size of small pebbles. The sediments of limestone are small shells. Which of the following is an example of erosion? A. Wind breaking down an existing rock into B. Layers of sediment pressed and sticking smaller pieces. together. C. Small shells being moved by water to the D. Animal fossils getting trapped between shore. sediment layers. 1 3. “Metamorphosis” means a change in form. Metamorphic rocks form when existing “parent” rocks change because of intense heat and/or pressure. The deeper a rock is in the Earth, the more pressure it is under. There is also pressure from the boundaries of tectonic plates pushing together. Heat can come from being exposed to the hot material below the Earth’s crust. Remember that metamorphic rocks don’t melt from heat--igneous rocks form from liquid rock. The heat and pressure that form metamorphic rock changes an existing rock’s structure. It’s like a ball of raw pizza dough being flattened and baked in the oven. It doesn’t melt, just changes form! Slate is a metamorphic rock formed from the sedimentary rock, shale. Gneiss is another metamorphic rock formed from granite, an igneous rock. Marble forms when limestone morphs from heat and pressure. Which of the following describes how metamorphic rock forms? A. Tectonic plate boundaries break apart an B. An igneous rock deep in the Earth is existing parent rock. exposed to hot material. C. Molten rock solidifies and hardens on top D. A parent rock is baked and melted into of the Earth’s crust. liquid rock in the Earth. 4. The rock cycle describes the formation, breakdown and reformation of rocks. It includes many processes that move and shape Earth’s materials. After an igneous rock forms, it can melt into magma and then cool into a new igneous rock. Or, weathering and erosion can break it into sediments that create a sedimentary rock. Otherwise, it may be heated and/or put under pressure, transforming into a metamorphic rock. Like igneous rocks, a metamorphic rock can break down into sediment and then become part of a sedimentary rock. A metamorphic rock can also melt into molten rock and cool into an igneous rock. If exposed to exposed to wind and water, a sedimentary rock can become sediment again. That sediment might be eroded, deposited and compacted as a new sedimentary rock. Or, like igneous rock, a sedimentary rock can be heated and put under pressure to become a metamorphic rock. Which of the following is true? A. Igneous rock can melt and cool to form B. Igneous rock can break into sediments new igneous rock. that will form a sedimentary rock. C. Metamorphic rock can break into D. All of the above. sediments that form sedimentary rock. 2 5. We identify types of rocks by how the rocks form. If you’re not sure what type of rock you’re holding, look for clues. Because igneous rocks form when magma and lava cool, they often have crystals. Crystals are clear, hard solids. The longer the rock takes to cool, the bigger the crystals will be. Basalt has large crystals because it cools slowly. Other igneous rocks cool so quickly that gas from the magma doesn’t have time to escape into the air before the magma turns solid. This leaves some igneous rocks, like scoria, with holes or spaces in them. Igneous rocks rarely contain fossils and are not layered. What do holes in igneous rocks indicate about the cooling process of the magma? A. The magma cooled too quickly for gas to B. The molten rock cooled slowly. escape. C. The magma cooled in layers. D. The rock cooled with fossils in each of the holes or spaces. 6. How can you tell if a rock is sedimentary? Again, thinking about how rocks form can help you. Look for particles, or sediment, in the rock—like sand, pebbles or shells—that might be stuck together. Sedimentary rocks tend to be softer than the other rock types. They also are much more likely to contain fossils. Some sedimentary rocks contain stripes due to the layers of sediment that form them. The red stone of Sedona, Arizona, are striped in this way. Those rocks are sandstone, a sedimentary rock. Which of the following would be a clue that a rock is sedimentary? A. No fossils or layers can be seen. B. There are small clear, hard crystals visible. C. The rock crumbles easily in your hand. D. There are ribbon-like bands of minerals. 7. Metamorphic rocks are a bit harder to identify because they can share traits with the other rock types. Again, thinking about the formation process can help. Metamorphic rocks have been heated and squashed. This can lead the minerals in them to line up, creating ribbon-like layers called bands. These rocks are called foliated metamorphic rocks. You can see these bands in gneiss. If a metamorphic rock has fossils, you know it was formed from a sedimentary rock. Because of the heat and pressure, the fossil will be hard to recognize and out of shape. Which of the following best describes foliated metamorphic rocks? A. There are easily recognizable fossils. B. The rock has ribbon-like layers of bands. C. They have crystals like igneous rocks. D. Different sized sediments can be seen. 3.
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