Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Each rock sample should be labeled with the appropriate number using a permanent marker, disc labels and Super Glue.
2. Label each rock as follows:

   Igneous

   1. Obsidian
   2. Gabbro
   3. Rhyolite
   4. Granite
   5. Basalt
   6. Scoria
   7. Pumice

   Sedimentary

   8. Sandstone
   9. Limestone, chemical
   10. Shale
   11. Rock salt
   12. Limestone, shell
   13. Coal
   14. Conglomerate
   15. Breccia

   Metamorphic

   16. Marble
   17. Gneiss

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

All materials may be saved for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All materials are reusable. This laboratory activity can reasonably be completed in two 50-minute class periods.
• Enlist the help of a teacher’s aide or another student for the labeling of the rocks.
• Super Glue may be helpful in placing the labeled discs on the rock specimens.
• Extra disc labels are provided for additional rock specimen labeling or if initial labels fall off.

Teacher Tips

• Have students use a textbook, rock guide or the Internet as additional resources, if desired.
• If the pumice rock has been used all day it might become too saturated and sink. Keep fresh pieces handy for later classes if needed.
• Have students identify unnumbered samples of the igneous, sedimentary and metamorphic rocks given in this kit.
• Have students research and/or identify other types of igneous, sedimentary and metamorphic rocks. Use actual gathered rock specimens and a rock field guide.
• Have students investigate the different types of fossils that can be preserved in sedimentary rocks.
• Investigate how various rocks respond to being heated in an oven.
• Have students research how rocks are used in our everyday lives.

Sample Data

Igneous Rock Classification Data Table

Part 1

Part 2 Sedimentary Rock Classification Data Table

Part 1 Part 2 Metamorphic Rock Classification Data Table

Answers to Questions

Igneous Rock

1. How are igneous rocks formed?

   Igneous rocks form from the cooling of molten material from volcanic activity. Magma that is trapped below the Earth’s surface is insulated by the rocks surrounding it. This holds in the heat and causes the magma to cool slowly. As the magma cools slowly, the atoms have enough time to arrange into large crystals called mineral grains. The mineral grain size is determined by how fast the magma cools. Rock forms as these mineral grains grow together.

2. Explain the difference between intrusive and extrusive igneous rocks.

   Igneous rocks that grow deep below the Earth’s surface and are cooled very slowly are known as intrusive igneous rocks. Extrusive igneous rocks are formed when lava cools at or near the Earth’s surface.

3. Rocks 3 and 4 both contain the same basic minerals. Other than the color, name a difference between these two rocks. Which one formed near the surface of the Earth and which one formed deeper in the Earth? How do you know?

   These two rocks have different grain sizes. Rock 3 formed near the surface of the Earth and rock 4 formed deeper in the Earth. Rock 4 has a larger grain size.

4. What is the main difference between rocks 2 and 5? Which one formed near the surface of the Earth and which one formed deeper in the Earth?

   These two rocks have different grain sizes. Rock 5 formed near the surface of the Earth and Rock 2 formed deeper in the Earth. Rock 5 has a smaller grain size.

5. What do you think caused the holes in rocks 6 and 7?

   Gases escaping while the rock was cooling caused the holes.

6. Are the textures of rocks 6 and 7 large-grained, fine-grained or vesicular?

   Vesicular.

7. One of the rocks 6 or 7 will float. Which of the rocks do you think will float? Place samples 6 and 7 in a beaker of water and see.

   The pumice rock should float. It is slightly less dense than water. The scoria is slightly more dense than water and should sink.

Sedimentary Rock

1. What are the three types of sedimentary rocks? How do they differ?

   There are three types of sedimentary rock—clastic, organic and chemical. Clastic sedimentary rocks are made of broken fragments of other rocks. These sediments are compacted and cemented together. Organic sedimentary rocks form from the remains of once living things. Chemical sedimentary rocks form from minerals dissolved in solution.

2. Which samples were the easiest to identify? Why?

   Answers will vary.

3. If a creek brought sediments into a lake and clastic rocks were formed, which type of rock from this activity would be found nearest the shoreline? Which one would be found the farthest from shore?

   The conglomerate will be found close to shore because it consists of the heaviest sediments. The shale will be found farthest from shore because it consists of the lightest sediment.

Metamorphic Rock

1. How do metamorphic rocks form?

   Metamorphic rocks are rocks that have changed due to temperature and pressure increases. Metamorphic rocks may be formed from changes in igneous, sedimentary or other metamorphic rocks.

2. What is the difference between foliated and non-foliated?

   When mineral grains flatten and line up in parallel bands, a metamorphic rock will have a foliated texture. In some metamorphic rocks, no banding occurs. The mineral grains change, grow and rearrange but they do not form bands. This process produces a non-foliated texture.

3. Look at samples 1–7. Which sample was most likely metamorphosed into gneiss? Why?

   Rock 4 granite. It consists of similar minerals as the gneiss.

4. Look at samples 8–15. Which sample was most likely metamorphosed into marble? Why?

   Rock 9 chemical limestone or 12 shell limestone. They both have a similar appearance to the marble.

5. Which type of rock will form in a lake in a region with a hot climate—igneous, sedimentary or metamorphic?

   The high temperature will cause excessive evaporation, causing many sediments to be precipitated as chemical sedimentary rocks.

6. Describe the appearance of the large sphere and small spheres after they were pressed together in Part B. What type of metamorphism caused this change?

   Answers will vary. Pressure caused the change.

7. Would this be defined as foliated or non-foliated texture? Explain.

   Foliated because banding is present.

Introduction

What is a rock and how are rocks formed? Examining and classifying rocks can help us understand not only how rocks are formed but also the transformation of rocks via the rock cycle.

Concepts

• Igneous rock
• Sedimentary rock
• Metamorphic rock
• Rock cycle

Background

Rocks are mixtures of minerals such as quartz, feldspar, mica and calcite, to name a few. The rock cycle shows how rocks change over time by a variety of physical and chemical processes (see Figure 1). Natural processes that are part of the rock cycle include weathering, erosion, lithification, metamorphism, melting and cooling. Weathering involves both the chemical and physical breakdown of rock at or near the Earth’s surface. This results in the accumulation of sediments—loose materials, such as rock and mineral fragments or pieces of animal and plant remains, that have been transported. Lithification is the transformation of sediment into a rock. The main processes involved in lithification are cementation—large sediments are held together by natural cements, and compaction—layers of sediments are compressed by the weight of the layers above them. Metamorphism is the process by which rocks are changed by heat, pressure, shear, stress or chemicals. Rocks are classified into three distinct groups—igneous, metamorphic or sedimentary—based on how they are formed.

Igneous rocks (the most abundant type of rock on Earth) are formed by the cooling of molten material from volcanic activity. Magma that is trapped below the Earth’s surface is insulated by the rocks surrounding it. This holds in the heat and causes the magma to cool slowly. As the magma cools slowly, the atoms have enough time to arrange into large crystals called mineral grains. The mineral grain size is determined by how fast the magma cools. Rock forms as these mineral grains grow together. The most common minerals found in igneous rocks are feldspar, quartz and biotite. Feldspar is generally a white or chalky-looking grain, quartz is a dark-gray glassy grain, and biotite is a small black grain. Intrusive igneous rocks grow deep below the Earth’s surface, are cooled very slowly and have a large grain size. Extrusive igneous rocks are formed when lava cools at or near the Earth’s surface. When lava cools on the Earth’s surface, it is exposed to air and moisture. Lava cools very quickly under these conditions, hence, only small mineral grains will form. Sometimes extrusive igneous rocks cool so rapidly that there is no time for crystals to form. This give rocks of this type a glassy appearance. Other extrusive igneous rocks form as gas bubbles pop which gives them a bubbly or vesicular appearance.

Sedimentary rocks form when sediments become pressed or cemented together or when sediments fall out of solution. Sediments are moved by erosion to a new location where they are deposited. As layer upon layer of sediment is settled in this location, pressure from the upper layers pushes down on the lower layers. The sediment then sticks together and forms solid sedimentary rock. There are three types of sedimentary rock—clastic, organic and chemical. Clastic sedimentary rocks are made of broken fragments of other rocks. These sediments are compacted and cemented together. Organic sedimentary rocks form from the remains of once living things. Chemical sedimentary rocks form from minerals dissolved in solution. Metamorphic rocks are rocks that have changed due to temperature and/or pressure increases.

Metamorphic rocks may be formed from changes in igneous, sedimentary or other metamorphic rocks. When mineral grains flatten and line up in parallel bands, a metamorphic rock will have a foliated or banded texture. In some metamorphic rocks, no banding occurs. The mineral grains change, grow and rearrange but they do not form bands. This process produces a non-foliated texture.

Experiment Overview

In this activity, the properties of igneous, metamorphic and sedimentary rocks will be investigated.

Materials

Safety Precautions

Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

I. Classifying Igneous Rocks

Part A

1. Examine rock samples 1–5 using a magnifier.
2. Determine the grain size or texture of each sample and record the observations on the Igneous Rock Classification Data Table. Note: Use descriptions such as fine-grained, large-grained or glassy.
3. Classify each rock sample as intrusive or extrusive on the Igneous Rock Classification Data Table.

Part B

4. Identify the minerals present in samples 1–5 (if any) using a magnifier, the Background information and your textbook.
5. Record the types of minerals present on the Igneous Rock Classification Data Table.

Part C

6. Examine rock samples 6 and 7 using a magnifier.
7. Record all observations on the Igneous Rock Classification Data Table.

Part D

8. In Part 2 of the Igneous Rock Classification Data Table, different types of igneous rocks are described in terms of their texture and mineral content. Read each description carefully and identify the rock sample number corresponding to each type of igneous rock.
9. Record the rock sample number corresponding to each rock name in Part 2 of the Igneous Rock Classification Data Table.
10. Answer the Igneous Rock Questions.

II. Classifying Sedimentary Rocks

Part A

1. Examine rock samples 8–15 using a magnifier.
2. Observe the color, texture, form and appearance of each rock sample and record all observations in the Sedimentary Rock Classification Data Table. Use the Background information to help identify features.

Part B

3. Use the Sedimentary Rock Classification Data Table to classify each rock sample 8–15.
4. Record the rock sample number corresponding to each rock name in Part 2 of the Sedimentary Rock Classification Data Table. Use the Background information to help identify features.
5. Answer the Sedimentary Rock Questions.

III. Metamorphic Rocks

Part A

1. Examine samples 16 and 17 using a magnifier.
2. Record all observations and determine the name for each of the samples on the Metamorphic Rock Classification Data Table. Use the Background information to help identify features.

Part B

3. Obtain 1-inch cubes of two different colors of modeling clay.
4. Mold one of the pieces of clay into a sphere.
5. Mold the other piece of clay into five smaller spheres.
6. Place the small spheres of clay onto the larger sphere of clay.
7. Slowly press down and flatten the clay.
8. Answer the Metamorphic Rock Questions.
9. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13531_Student1.pdf