1. Metamorphic Rocks Chapter 2 Section 4 p. 44 - 49 Vocabulary: 1. foliated 2. nonfoliated

2. Origins of Metamorphic Rock p. 44 Rocks can also go through a process call metamorphism. This word comes from the Greek words meta, which means “changed” and morphos, which means “shape.” Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have changed. If the temperature or pressure of the new environment is different from the one in which the rock formed, the rock will undergo metamorphism. It is the depth and pressure at which metamorphic rocks form that allows the rock to heat to very high temperatures and still keep its solid form. Large movements within the crust of the Earth add additional pressure during metamorphism.

3. Contact Metamorphism p. 45 One way rock can undergo metamorphism is by being heated by nearby magma. When magma moves through the crust, the magma heats the surrounding rock and changes it. The greatest change takes place where magma comes into direct contact with the surrounding rock. The effect of heat on rock gradually decreases as the rock’s distance from the magma increases and as temperature decreases. Contact metamorphism occurs near igneous intrusions.

4. Regional Metamorphism p. 45 When pressure builds up in rock that is buried deep below other rock formations or when large pieces of the Earth’s crust collide with each other, regional metamorphism occurs. The increased pressure and temperature causes rock to become deformed and chemically changes. Regional metamorphism occurs over thousands of cubic kilometers deep within the Earth’s crust. Rocks that have undergone regional metamorphism are found beneath most continental rock formations.

5. Composition of Metamorphic Rock p. 46 Metamorphism occurs when temperature and pressure inside the Earth’s crust change. The original minerals change into minerals that are more stable in the new conditions. Some metamorphic minerals form only at certain temperatures and pressures. These minerals, known as index minerals, are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism.

6. Textures of Metamorphic Rock p. 47 All metamorphic rock has one of two textures – foliated and nonfoliated. Foliated Metamorphic Rock The texture of metamorphic rock in which the mineral grains are arranged in planes or bands is usually called foliated. It usually contains aligned grains of flat minerals. What you see in this picture is an example of a sedimentary rock called shale. When it is exposed to slight heat and pressure, the clay minerals change into mica minerals. The shale becomes slate. The process continues until it becomes the metamorphic rock known as gneiss.

7. Nonfoliated Metamorphic Rock p. 46 The texture of metamorphic rock in which the mineral grains are not arranged in planes or bands is called nofoliated. Nonfoliated rocks are commonly made of one or only a few minerals. During metamorphism, the crystals of these minerals may change in size or the mineral may change in composition in a process called recrystallization. The marble and quartzite shown here are examples of sedimentary rocks that have recrystallized during metamorphism.

8. Metamorphic Rock Structures p. 49 Metamorphic rocks can tell you something about their history by looking at the rock’s changes through a process called deformation. Deformation is a change in the shape of a rock caused by a force placed on it. Folds, or bends in metamorphic rock are structures that indicate that a rock has been deformed.

10. Quiz Time! 2. Explain the difference between contact metamorphism and regional metamorphism. Contact metamorphism occurs near igneous intrusions where magma comes into direct contact with surrounding rock. Regional metamorphism occurs when large pieces of Earth’s crust collide causing rock to become deformed and chemically changed. 1. What does a metamorphic rock need to form? heat and pressure

11. 3. Why is marble considered a nonfoliated metamorphic rock? Its mineral grains are not arranged in planes or bands. 4. What does the composition of a metamorphic rock tell you about the rock’s origin and formation? Different metamorphic minerals indicate the temperature and pressure conditions that existed when the rock formed. Science Humor… What did the marble say to the slate? Don’t take me for granite!