Chapter 8 Lesson 4, "Metamorphic Rocks"

Materials:

• Mineral kit samples, (40, 35, 38, 33, 39, 31)
• Worksheet, "Metamorphic Rocks"

Objective:

• Students will explain how metamorphic rocks form.
• Students will identify samples of foliated and nonfoliated metamorphic rocks.

Anticipatory Set:* Show the students a series of pictures of a caterpillar turning into a butterfly series (1, 2, 3, 4). Ask them for the word that is used to describe the change the caterpillar goes through to turn into the butterfly. (Metamorphosis) Tell them that rocks go through a huge change as well deep under the surface of the earth because of intense heat (above 320 degrees C)and pressure. The igneous and sedimentary rocks are twisted, squeezed, and bent as hot fluids move around the rocks. What is the term for those types of rocks? Metamorphic Foliation and Creation

Students will be given six samples of rock. Tell them that one of these rocks turns into another of the rocks. There are three pairs. Try to match up the parent rock to the metamorphic rock that it turns into. 40 Marble comes from 35 limestone; 39 Schist can come from a lot of different combinations but can come from 31 Granite; Slate 38 mainly comes from 33 shale.)

Teacher Input:* Tell the students that there is different kinds of stress put on rock as it lies under the surface. The most common place the stress can come from is plate tectonics. The stress and pressure can have a lot of effects on the rocks. It can straighten crystals, take rounded stones in sedimentary rocks and flatten them and twist different layers of rock.

Geologists divide metamorphic rocks into two categories Foliated and Non foliated. In foliated rock minerals have been rearranged into visible bands. Here are some examples:

• Slate Slates form at low metamorphic grade by the growth of fine grained chlorite and clay minerals. The preferred orientation of these sheet silicates causes the rock to easily break along the planes parallel to the sheet silicates, causing a slate cleavage. (Slate diagram, Slate Rock)
• Schist - The size of the mineral grains tends to enlarge with increasing grade of metamorphism. Eventually the rock develops a near planar foliation caused by the preferred orientation of sheet silicates (mainly biotite and muscovite). Quartz and Feldspar grains, however show no preferred orientation. The irregular planar foliation at this stage is called schistosity. (Schist diagram, Schist rock)
• Gneiss As metamorphic grade increases, the sheet silicates become unstable and dark colored minerals like hornblende and pyroxene start to grow. These dark colored minerals tend to become segregated in distinct bands through the rock, giving the rock a gneissic banding. Because the dark colored minerals tend to form elongated crystals, rather than sheet- like crystals, they still have a preferred orientation with their long directions perpendicular to the maximum differential stress.(Gneiss diagram, Gneiss rock)

The second type is Nonfoliated Rock in which the rock does not show bands because it is made from one basic type of material. This is a harder type of rock Here are some examples:

• Marble - Since limestones are made up of essentially one mineral, Calcite, and calcite is stable over a wide range of temperature and pressure, metamorphism of limestone only causes the original calcite crystals to grow larger. Since no sheet silicates are present the resulting rock, a marble, does not show foliation.Many uses; Building, Artwork, fountains and furniture.Difficult to mine because large pieces are needed by sculptures and builders.
• Quartzite - Metamorphism of sandstone originally containing only quartz, results in re crystallization and growth of the quartz, producing a non foliated rock called a quartzite. Can be used many ways but must commonly as building products.

Guided Practice:* Students will work together to answer the questions at the end of the section on Page 193.

Independent Practice:* Students will complete the Worksheet, "Metamorphic Rocks"

Check for Understanding:* Students will complete the quiz on "Metamorphic Rocks"

Duration:

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).

Alaska Content Standards Addressed in this lesson:

• SCI A-9 Students will understand the transfers and transformations of matter and energy that link living things and their physical

• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge); and: