Igneous and Metamorphic Rocks

Active learning works for this topic because students need to connect abstract processes like cooling rates and pressure to visible textures and structures. When students manipulate materials, observe changes, and discuss their findings, they build mental models that connect crystal size to formation conditions.

• 6th Grade
• Science
• 4 activities
• 15 min–40 min

Learning Objectives

1. Classify igneous rocks as intrusive or extrusive based on crystal size and formation environment.
2. Explain the transformation of existing rocks into metamorphic rocks through the processes of heat and pressure.
3. Analyze the relationship between cooling rate and crystal size in igneous rocks, connecting texture to origin.
4. Compare the mineral composition of parent rocks to their metamorphic equivalents, such as limestone to marble.

Inquiry Circle

⏱ 40 min·Small Groups

Inquiry Circle: Cooling Rate Crystal Lab

Groups grow alum crystals under different cooling conditions including an ice bath, room temperature, and a warm water bath. They compare crystal sizes under hand lenses and connect their findings to the textural differences between intrusive and extrusive igneous rocks.

Prepare & details

Differentiate between intrusive and extrusive igneous rocks.

Facilitation Tip: During the Socratic Discussion about marble, sit in the circle with students to model turn-taking and prompt quieter students with questions like, 'What changed in your rock sample when you applied heat and pressure?'

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Gallery Walk

⏱ 30 min·Small Groups

Gallery Walk: Rock Texture Stations

Rock samples including granite, basalt, obsidian, pumice, gneiss, and quartzite are displayed at stations. Students record crystal size, luster, and banding for each sample, then write a brief 'formation story' explaining what conditions the rock experienced.

Prepare & details

Explain how the heat and pressure of Earth's interior recycle old rock.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: Intrusive vs. Extrusive

Present two unlabeled rock photographs and ask partners to determine which is intrusive and which is extrusive based on texture alone. Each pair defends their reasoning before comparing conclusions with adjacent pairs.

Prepare & details

Analyze what the texture of an igneous rock reveals about its cooling history.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Gallery Walk

⏱ 20 min·Whole Class

Socratic Discussion: Marble's Identity

Pose the question: if marble and limestone are both made of calcite, why are they classified as different rock types? Students use evidence about heat, pressure, and crystal structure to build a class consensus about what makes a metamorphic rock distinct.

Prepare & details

Differentiate between intrusive and extrusive igneous rocks.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Teaching This Topic

Teach this topic by starting with observable textures before introducing processes. Research shows students grasp solid-state transformations better when they first manipulate physical models. Avoid beginning with definitions—instead, let students discover concepts through structured exploration, then formalize the vocabulary together.

What to Expect

Students will explain how cooling rates create different crystal sizes in igneous rocks and describe how heat and pressure change rocks without melting them. They will use specific vocabulary like intrusive, extrusive, and recrystallization to justify their observations.

Watch Out for These Misconceptions

Common Misconception

During the Cooling Rate Crystal Lab, watch for students using 'lava' and 'magma' interchangeably when describing their sugar crystal setups.

What to Teach Instead

Ask students to relabel their setups with the correct terms and explain why the environment (below or above ground) matters for crystal growth, using their sugar crystals as evidence.

Common Misconception

During the Gallery Walk: Rock Texture Stations, watch for students assuming that any rock changed by heat must have melted.

What to Teach Instead

Have students act out recrystallization by pressing and rearranging blocks of clay to show how pressure changes shape without melting, then relate this to the metamorphic rock samples at their station.

Common Misconception

During the Cooling Rate Crystal Lab, watch for students classifying obsidian as a mineral due to its smooth, glassy texture.

What to Teach Instead

Use the lab’s microscopes or magnifiers to show students that obsidian lacks visible crystals, then explain that minerals must have an ordered atomic structure, which obsidian does not have.

Assessment Ideas

Quick Check

After the Gallery Walk: Rock Texture Stations, provide students with images of granite and basalt. Ask them to identify each rock type, state whether it is intrusive or extrusive, and write one sentence explaining how its texture indicates its cooling rate.

Discussion Prompt

During the Think-Pair-Share: Intrusive vs. Extrusive, pose the question: 'Imagine a large mountain range forming. What types of rock transformations are likely occurring deep within the Earth's crust, and why?' Listen for students to discuss heat, pressure, and the formation of metamorphic rocks.

Exit Ticket

After the Cooling Rate Crystal Lab, have students draw a simple diagram showing magma cooling underground versus lava cooling on the surface. Label the resulting rock types and briefly explain the difference in crystal size.

Extensions & Scaffolding

• Challenge early finishers to research and present on how the crystal sizes in pegmatite (a type of intrusive igneous rock) differ from granite and why.
• Scaffolding for struggling students: Provide a word bank and sentence frames during the Cooling Rate Crystal Lab, such as 'The ______ cooled slowly, so it formed ______ crystals.'
• Deeper exploration: Have students research how metamorphic foliation relates to the original rock’s mineral composition and present their findings in a short video.

Key Vocabulary

Magma	Molten rock found beneath the Earth's surface. When magma cools and solidifies, it forms intrusive igneous rocks.
Lava	Molten rock that erupts onto the Earth's surface. When lava cools and solidifies, it forms extrusive igneous rocks.
Intrusive igneous rock	Igneous rock formed from magma that cools slowly beneath the Earth's surface, resulting in large, visible crystals.
Extrusive igneous rock	Igneous rock formed from lava that cools quickly on the Earth's surface, resulting in small, fine-grained crystals.
Metamorphic rock	A rock that has been changed from its original form by heat, pressure, or chemical reactions, without melting completely.