• Assess the cooperation of each student in small-group discussions.

• Assess worksheet responses in terms of student usage of scientific vocabulary and understanding of the metamorphic rock-forming processes.

“We’re going to conclude our investigation of the three basic rock types today. In Lesson 1, we analyzed igneous rocks; in Lesson 2, sedimentary rocks. What is the third basic rock type?” (metamorphic) “The term metamorphic comes from the Greek words for change (meta) and form (morphe). So, metamorphic rocks are rocks that have been changed somehow. Do you think these changes would involve melting?” (No. Melting is an igneous rock process.) “Do you think the changes would involve weathering into sediments?” (No. Weathering is a sedimentary rock process that happens at the Earth’s surface.) “So the changes that a pre-existing (parent) rock undergoes to become a metamorphic rock would have to be changes that occur while the rock is in the solid state and changes that occur deep within the Earth’s crust. Otherwise, an igneous or sedimentary rock would be formed instead of a metamorphic rock. Let’s see what types of changes are metamorphic changes.”

Show students images of metamorphic rocks (S-6-1-3_Metamorphic Rock Pictures.doc). Divide students into groups and distribute the metamorphic rock specimens. “These are specimens of the metamorphic rocks slate, quartzite, marble, and gneiss. They are specimens of rocks that have undergone changes while remaining solid and deep within the Earth’s crust.” Distribute the magnifying lenses and the Metamorphic Rock Worksheet (S-6-1-2_Sedimentary Rocks Worksheet and KEY.doc). Instruct students to examine the specimens and complete questions 1 through 6 on the worksheet. Monitor students, providing feedback. Facilitate a short class discussion. “Each of these rock specimens started out as a parent rock (pre-existing rock) that was changed into a metamorphic rock by Earth processes. Let’s see what kinds of changes these rocks went through.”

Distribute the mineral and rock specimen sets from Lessons 1 and 2. Students complete the Metamorphic Rocks worksheet as the class engages in the activities.” Let’s start with the metamorphic rock gneiss. Granite is the igneous parent rock for this particular gneiss specimen. Remember, granite is made of the minerals feldspar, biotite, and quartz. Examine your granite specimen. Look for the feldspar, biotite, and quartz crystals that make up the granite. Can you recognize them?” Monitor students, providing feedback. “Now examine your gneiss specimen. Do you see crystals of feldspar, biotite, and quartz?” Monitor students, providing feedback. “The granite and gneiss specimens, then, contain the same minerals. Is there a difference in how the mineral crystals are arranged in the gneiss as compared to the granite?” (Yes. There are bands of light and dark minerals in the gneiss.) “Since metamorphic rocks form deep within the Earth’s crust, they form under high temperature/high pressure conditions. The parent rock granite did not melt when changing into gneiss, but its minerals did recrystallize to adjust to the high temperature and high pressure the rock was subjected to. The banding is due to this recrystallization. The crystals grew perpendicular to the direction of pressure, with the light and dark minerals separating out. So, in case of the granite changing to gneiss, the granite crystals regrew parallel to each other, creating the banding characteristic of the gneiss.” Monitor students as they complete the worksheet, providing feedback.

“Now, let’s compare sandstone and quartzite. Sandstone is the sedimentary parent rock of the metamorphic rock quartzite. How can you distinguish the sandstone specimen from the quartzite specimen? How did the sandstone change into quartzite?” Facilitate class discussions. Monitor students as they examine the rock specimens and complete the worksheet.

“Find the limestone specimen and the marble specimen. Limestone is the sedimentary parent rock of the metamorphic rock marble. How can you tell the limestone from the marble? How did the limestone change into marble?” Facilitate class discussions. Monitor students as they examine the rock specimens and complete the worksheet.

“Find the shale specimen and the slate specimen. Shale is the sedimentary parent rock of the metamorphic rock slate. How can you tell the shale from the slate? How did the shale change into slate?” Facilitate class discussions. Monitor students as they examine the rock specimens and complete the worksheet. Collect the rock and mineral specimens and the magnifying lenses. Instruct students to wash their hands and clean up their work areas.

Have students return to their desks and instruct them to complete question 11 on the Metamorphic Rock worksheet. Monitor students, providing feedback. In order to dispel possible misconception, explain to students: “We worked with metamorphic rock samples that came from only igneous and sedimentary parent rocks today. However, metamorphic rocks can form from metamorphic parent rocks as well. For example, if slate is exposed to higher temperature and pressure, it will become a rock called schist. If the schist is exposed to even higher temperature and pressure, it will become gneiss (a different kind of gneiss than the granitic gneiss because slate is its parent rock). So, metamorphic rocks can form from igneous, sedimentary, or metamorphic parent rocks.”

Hand out to students the metamorphic rock essay question (S-6-1-3_Metamorphic Rock Essay Questions and Rubric.doc). Instruct students to respond to the following question in complete sentences and in paragraph form. They may refer to their notes and worksheet (especially column titles in question 11) when composing their paragraphs. Student paragraphs need not go into specific detail for the rock samples.

Explain what metamorphic rocks are and how they form. Your explanation must include: 1) a general explanation of what metamorphic rocks are; 2) a description of the general conditions under which metamorphic rocks form; 3) a summary of the two general types of changes that transform parent rocks to metamorphic rocks; and 4) an explanation of what parent rocks are.

Extension:

• Students who might need opportunities for additional learning can compare the process of metamorphism to something common in the average household: baking. Students can melt chocolate, wax, butter, etc. over a safe heat source and record observations during the process. They can then place the liquid in its container on a bag of ice, where they will continue to make observations while the liquid is solidifying. When the liquid has solidified, they will match the steps in the baking process to the steps in metamorphosis (heating, liquidification, cooling, and solidifying) as well as the heat and cold sources found in each circumstance.

• Students who may be going beyond the standards can research metamorphic rocks in Pennsylvania and write an essay relating metamorphism to mountain building processes.