# Model the Rock Cycle with Crayons

## Summary

6th-8th
Group Size
2-3 students
Active Time
1 hour
Total Time
1 hour
Area of Science
Geology
Key Concepts
Rock cycle, types of rocks
Credits
Ben Finio, PhD, Science Buddies
Starburst is a registered trademark of Wm. Wrigley Jr. Company.
Crayon Rock Cycle

## Overview

Can one type of rock turn into another type of rock? In this lesson plan, your students will explore the rock cycle and model it using crayons. Can they turn a sedimentary "rock" made from crayon shavings into a metamorphic rock? What about an igneous rock? Try this lesson to find out!

## Learning Objectives

• Understand the cycling of matter that forms rocks inside Earth and on Earth's surface.
• Explain how crayons can be used to model the rock cycle.

## NGSS Alignment

This lesson helps students prepare for these Next Generation Science Standards Performance Expectations:
• MS-ESS2-1. Develop a model to describe the cycling of Earth's materials and the flow of energy that drives this process.
This lesson focuses on these aspects of NGSS Three Dimensional Learning:

 Science & Engineering Practices Disciplinary Core Ideas Crosscutting Concepts Science & Engineering Practices Developing and Using Models. Develop and use a model to describe phenomena. Disciplinary Core Ideas ESS2.A: Earth's Materials and Systems. All Earth processes are the result of energy flowing and matter cycling within and among the planet's systems. This energy is derived from the sun and Earth's hot interior. The energy that flows and matter that cycles produce chemical and physical changes in Earth's materials and living organisms. (MS-ESS2-1) Crosscutting Concepts Systems and System Models. Models can be used to represent systems and their interactions—such as inputs, processes, and outputs—and energy, matter, and information flows within systems. Scale Proportion and Quantity. Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small.

## Materials

Each group will need:

• Crayons (at least 2, each a different color)
• Potato peeler, paring knife, or cheese grater
• Aluminum foil (1 sheet)
• Access to a frying pan and stove, or a hot plate
• Tongs or oven mitts
• Toothpicks (several)
• Small bowls (one for each crayon color)
• Ice water

## Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

The rock cycle describes the cycling of matter on and within Earth, which results in the three main types of rocks: sedimentary, metamorphic, and igneous (Figure 1).

• Sedimentary rocks are formed when small particles (like sand and dust) are compressed together in layers.
• Metamorphic rocks are formed when existing rocks are changed by heat and pressure.
• Igneous rocks are formed when other types of rocks melt, forming magma, and then re-cool into solid rocks.

Figure 1. From left to right, examples of the three types of rock: a sedimentary rock, a metamorphic rock, and an igneous rock. Note that while distinct layers are clearly visible in the sedimentary and metamorphic rocks pictured here, that might not always be the case.

Each type of rock can turn into other types of rock through various processes within Earth or on Earth's surface (Figure 2). For example:

• Rocks can be broken into smaller pieces by weathering and erosion. These pieces accumulate to form layers (deposition), and are gradually compressed (lithification) to form sedimentary rocks.
• Rocks can be heated and compressed by the high temperatures and pressures under Earth's surface in a process called metamorphism. This deforms them and turns them into metamorphic rocks.
• Rocks can be melted by the high temperatures beneath Earth's surface, forming magma. When magma cools—either when it crystallizes below Earth's surface, or when it emerges through a volcano and is exposed to water or air—it forms igneous rocks.

rock cycle diagram showing igneous rock, metamorphic rock, sedimentary rock, and magma with the following transitions: All three types of rocks can turn into magma by melting; Magma turns into igneous rock by crystallizing; Igneous and metamorphic rocks turn into sedimentary rock by erosion, deposition, and lithification; Igneous and sedimentary rocks turn into metamorphic rocks by metamorphosis

Figure 2. The rock cycle, showing how sedimentary, metamorphic, and igneous rocks can each turn into the other types. (Wikimedia Commons user Actualist, 2013. CC BY-SA 3.0).

In this lesson plan, your students will develop a model for the rock cycle using crayons. First they will use a sharp kitchen utensil (like a knife, potato peeler, or cheese grater) to make crayon shavings. These crayon shavings can be compressed in layers to form a sedimentary "rock". From there, students will explore how they can turn their sedimentary rock into other types of rocks, and whether they can change the other types of rock back. They will develop analogies for how processes that they use in the classroom (like pressing the crayon shavings together or heating them on a hot plate) relate to processes that occur within Earth, such as lithification (the process in which sediments compact under pressure) or heating from Earth's core.

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