& Identify Rocks
suggested grade levels: 9-12
view Idaho achievement standards for this lesson
|Rock identification book||Adhesive tape|
|Strong canvas bag||Gloves|
|Chisel||Unglazed white tile|
|Newspaper||Egg carton or muffin tin|
|Notebook and pencil|
Use the geology section of the Digital Atlas of Idaho. To get there: Click on Atlas Home, Geology, Basics, then on Diagrams. Also use the rock section for a description of different rocks. To get there: Click on Idaho Overview, then on Rocks. Encourage your students to examine the rock cycle and click on the diagram for the explanations on the different types of rock. Explain to the students that they will need to know this in order to do this field activity.
Encourage your students to collect and identify rock specimens at home:
1.Try to pick fairly large rock specimens. Use the size of a closed fist as your goal. If you are working in an excavation, collect samples from all layers. When you find a rock you want to keep, stick a small piece of adhesive tape on it. Number the rock and make an entry in your notebook, next to the corresponding number, describing where the rock was found. Wrap the marked rock in newspaper and drop it into your bag. Use the sample as a guide to decide how certain land formations came into being.
2. If you want to group your rocks according to whether they are igneous, sedimentary, or metamorphic, use the following general description of the three kinds of rocks and compare your samples with the classification pictures. Sedimentary rocks have a layered appearance but usually break easily and feel gritty. Igneous rocks have a crystalline appearance, with the crystals mixed and never in layers. Metamorphic rocks are very hard and more crystalline than igneous rocks, but the crystals of each mineral are lined up in bands or layers.
3. Remember that the outside surfaces of a rock are weathered, and you must expose a fresh surface if you wish to study the original characteristics of the rock. Use the hammer to break the rock open so that you can see a clean interior surface.
4. Now that you have collected a number of rock samples and have made notes about where the samples were found, it is time to identify or grade them. There are several techniques you can use to help with this identification: the acid test, the cleavage test, and the streak test. The acid test is very simple. Rocks containing calcite or lime will bubble or fizz when an acid is poured on them. Use vinegar as your acid. If you hold the rock close to your ear and listen carefully, you'll be able to hear any fizzing that might be taking place.
5. When you break rocks, they will either cleave (an easy, flat break) or fracture, depending on the minerals present in them. Some cleavages are good clues to identifying minerals in rock. The way a rock fractures is also a clue to its identity. Hit the rock with a hammer to break it. Place a cloth over the rock before you hit it so that chips won't fly.
6. When you scratch a piece of unglazed white porcelain (the back of a bathroom tile will do) with certain rocks, they make characteristic streaks. For example, although pyrite in rock form looks yellow, it always leaves a black streak on the tile. Noting the streak it makes can identify many rocks.
These are links to access the handouts and printable materials.
Diagrams | Rocks