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Name ______________________________ Lesson 3 Summary Use with pp. 208–213 Lesson 3: How are rocks classified? Vocabulary igneous type of rock that forms from molten rock sedimentary type of rock that forms when layers of sediments settle on top of one another and harden metamorphic type of rock formed when heat and pressure change the properties of rock Rocks are classified by how they form, or are made. Below Earth’s surface, rocks get so hot that they become melted, or molten. Molten rock is called magma. Igneous rocks are made from magma. Igneous rocks are usually hard. They do not have layers. They often have crystals that interlock, or fit together. Magma erupts to Earth’s surface through volcanoes. When molten rock reaches the surface, it is called lava. Magma Cooling Quickly On Earth’s surface, lava cools quickly. Some igneous rocks are made from lava that cools quickly. These rocks have small crystals. Pumice and basalt are rocks that form when lava cools quickly. Magma Cooling Slowly Some igneous rocks are made below Earth’s surface. Magma below Earth’s surface cools very slowly. The magma forms igneous rocks with large crystals. Granite is an igneous rock. It forms when magma cools slowly. Granite has large crystals of quartz, feldspar, and mica. Granite is very hard. Sedimentary Rocks Sediments are made of soil, shells, small pieces of rock, and dead plant and animal matter. Water, wind, ice, and gravity can move sediments from one place to another. Sediments settle and gather on the bottoms 40 Chapter 6, Lesson 3 Summary of rivers, lakes, and oceans. Sedimentary rocks form when layers of sediments settle on top of each other. The weight of the layers pushes the sediments together. Sticky clay minerals also hold the sediments together. The layers gradually get harder and form rocks. The layers on top are usually the newest, and the layers on the bottom are the oldest. This means that fossils in a lower layer of rock are older than fossils in a higher layer. Sedimentary rocks are usually soft and have layers. They are made of different sediments. Limestone is made of the shells of tiny sea animals that lived long ago. Metamorphic Rock It is very hot inside the Earth. There is also a lot of pressure. The rocks above squeeze and press on the rocks below. The heat and pressure together can change the properties of rocks. This makes metamorphic rocks. Metamorphic rocks can be made from sedimentary rocks, igneous rocks, or other metamorphic rocks. The heat and pressure can change the crystals in a rock. The crystals can be a different size or shape. Sometimes new minerals form. Metamorphic rocks are usually hard. They can break into flat sheets or slabs. Slate is a metamorphic rock with thin layers. Intervention Study Guide © Pearson Education, Inc. 4 Igneous Rocks Name ______________________________ Lesson 3 Questions Use with pp. 208–213 Lesson 3 Questions 1. What are the three types of rocks? 2. What are igneous rocks made from? 3. What is limestone made of? What type of rock is limestone? © Pearson Education, Inc. 4 4. What is one example of a metamorphic rock? Intervention Study Guide Chapter 6, Lesson 3 Questions 41