Display an apple for the class to view. Facilitate a class discussion of the physical characteristics of the apple. “Tell me what you see.” (an apple) “How do you know it’s an apple just by looking at it?” Note student comments (color, shape, size, etc.) on the board.
“In science class, what would we call these comments you made on the apple?” (observations) “What are your observations describing?” (physical properties of the apple) “So, physical properties are . . .” Facilitate a class discussion and post the class definition on the board. (In general, physical properties are characteristics of an object that can be observed without changing what the object is made of.) “How did we use the physical properties of the apple?” (to describe its appearance so we could identify the object as an apple) “So one use of the physical properties of an object is to help us identify what an object is. Today, we’ll be using physical properties of rocks to help us figure out what types of rocks they are and how they formed.”
“What are rocks and minerals, and how are they related to each other?” Facilitate a short class discussion guiding students to learn that rocks are naturally occurring solid mixtures of minerals (and sometimes nonminerals like volcanic glass or coal). Minerals are naturally occurring, solid crystalline substances. Examples of rocks are granite, sandstone, and slate. Examples of minerals are quartz, calcite, and feldspar. “The rock specimens we will examine today belong to a large group of rocks called igneous rocks.” Show students images of igneous rocks (S-6-1-1_Igneous Rock Pictures.doc). “An igneous rock forms through the solidification of magma or lava (hot molten rock). The term igneous comes from the Latin ignis, which means fire. Let’s take a look at some minerals that make up a common igneous rock called granite.”
Divide students into small groups and hand out copies of the Physical Properties of Igneous Rocks Worksheet (S-6-1-1_Physical Properties of Igneous Rocks Worksheet and KEY.doc). Explain and demonstrate how to use a magnifying lens properly. “You will be using a magnifying lens to examine rock and mineral specimens as part of our lesson today. Please leave the specimens on the table as you observe them. Remain sitting upright and slowly move the lens towards the specimen until the image of the specimen comes into focus. Do not place the lens close to your eyes; the lenses are not sterile. Do not allow the lenses to touch the specimens; the lenses will get scratched. Carefully place the lenses back into the box when they are not in use.” Distribute the mineral boxes and magnifying lenses. “Examine the mineral specimens and complete Part I of the worksheet. Be prepared to contribute your findings to a class discussion.” Monitor students and give feedback as students examine the specimens, noting physical properties that would help them identify the minerals. Instruct students not to peel off sheets of the biotite. Facilitate a short class discussion of student observations. Physical properties listed could include color, shape, luster, or unusual appearance.
“I’m going to distribute a specimen of the rock, granite, to each group. Examine the specimen and complete Part II of the worksheet. Be prepared to report your findings to a class discussion.” Monitor students and give feedback as students complete Part II of the worksheet. Facilitate a short class discussion of student findings. Instruct students to return the mineral box, keeping the granite specimen and magnifying lenses.
“We’ll be investigating three more rock specimens: basalt, pumice, and obsidian.” Distribute the igneous rock boxes to the groups. “Complete Part III of the worksheet. Be prepared to contribute to a class discussion of group results.” Monitor students and provide feedback. Facilitate a short class discussion of their results, noting similarities and differences in grouping characteristics.
“Rocks composed of minerals can be classified (grouped) by overall color and the size of the crystals that make them up. Examine the granite and basalt specimens and complete Part IV of the worksheet. Be prepared to contribute to a class discussion of group results.” Monitor students and provide feedback. Facilitate a short class discussion of their results.
“Some rocks are made of natural glass. Minerals are made of patterns of particles of matter that can be translated to fill space, just like tessellations in math class. Glass is made of irregular patterns of matter that do not translate well. Let me show you what I mean.” Project the images of a crystalline vs. a noncrystalline (glass) arrangement of particles of matter found at http://www.benbest.com/cryonics/noncryst.gif —point out the irregularities in the glass particle patterns.
“Pumice is an igneous rock made of natural glass that contains a lot of spaces. These spaces were left by air bubbles that formed when very sticky lava was blown out of a volcano. It feels very light in weight, doesn’t it? By the way, what’s the difference between lava and magma?” (Lava is magma that erupts on top of the surface of the Earth. Magma is molten rock beneath the surface of the Earth.) “Obsidian is a natural volcanic glass erupted onto the surface of the Earth. Obsidian can be most any color. Be careful when examining these rock specimens because the edges can cut you. Examine these rock specimens with the magnifying lens. You may see a few crystals included within the glass. Complete Part V of your worksheet. Be prepared to contribute to a class discussion of group results.” Monitor students and provide feedback. Facilitate a short class discussion of their results.
“As we examined each of the four igneous rock specimens today, we noted whether the rock specimen was composed mainly of larger mineral crystals that we could see without using the magnifying lens, whether it was composed of crystals too small to see well (even with a magnifying lens), or whether it was composed mainly of glass (maybe just a few crystals). Let’s see what controls whether or not crystals develop or whether crystals grow large or stay small.”
Distribute the igneous rock formation worksheet (S-6-1-1_Formation of Igneous Rocks Worksheet and KEY.doc). Model and explain how to perform the activity. Distribute materials to the groups. Instruct students to assign roles (timekeeper, recorder, macaroni transfer technician, materials manager). Monitor students during the activity and while completing the questions on the worksheet, providing feedback.
When students have completed the activity, have them return to their desks. Continue the lesson with the following assignment: “To show what you have learned today, complete the Lava and Magma worksheet” (S-6-1-1_Lava and Magma Sketch.doc). “Directions are listed on the worksheet.”
An extension for all students is to make rock candy in the classroom to demonstrate crystal growth in the formation of igneous rocks. Follow the directions on the Rock Candy Directions (S-6-1-1_Rock Candy Directions.doc). Throughout, have students make connections between the crystal growth in different types of igneous rocks and the candy being formed.
Students who may need opportunities for additional learning can use a teacher-made reference sheet, which includes basic vocabulary definitions and visuals, throughout the lesson’s activities. The reference sheet will serve as a modification for students who need extra practice with the standards. You may also provide students with worksheets with appropriately modified questions and material to suit individual student needs.
Students who may be going beyond the standards can investigate tektites (meteoric glass), decide whether tektites should be classified as igneous rocks, write a short essay that states their opinion, and defend their position with at least three supporting details.