📖 Lesson 3: Types and Formation of Rocks

👩🏽‍🏫 Introduction

Hello explorer of the Earth! 🌍

When you walk on the ground, climb a hill, or visit a beach, you’re standing on rocks. These aren’t just random stones—they are Earth’s memory books, telling stories about volcanoes, rivers, mountains, and even ancient creatures.

In this lesson, we’ll discover how rocks form, the three main types of rocks, and how they change over time. By the end, you’ll know why some rocks sparkle, others crumble, and how rocks help us understand Earth’s past and build its future.

📘 Core Concepts

🔹 What Are Rocks?

A rock is a natural solid material made of one or more minerals. Rocks are found in the Earth’s crust and form the base of landscapes and soil.

🔹 The Three Main Types of Rocks

Rocks are grouped based on how they form. Here are the three main types:

1. Igneous Rocks – “Born from Fire” 🔥

Formed when molten rock (magma or lava) cools and hardens.

📌 Real-life example: Lava from a volcanic eruption cools to form basalt.

2. Sedimentary Rocks – “Layered Stories” 🏞️

Formed from particles of other rocks or remains of plants and animals that are pressed together in layers over time.

📌 Examples: Sandstone, limestone, shale
🦴 May contain fossils!

3. Metamorphic Rocks – “Changed by Pressure & Heat” 🔁

Formed when existing rocks (igneous or sedimentary) are changed by heat and pressure—but don’t melt.

📌 Used in: Building materials and sculptures (e.g. marble floors).

🔁 The Rock Cycle

Rocks are constantly changing through a cycle:

1. Magma cools → Igneous rock

2. Weathering → Sediments

3. Compaction → Sedimentary rock

4. Heat & pressure → Metamorphic rock

5. Melting → Magma again

📍 Diagram Suggestion: Draw a circular flow with arrows showing the rock cycle.

🧩 Sample Problem Walkthrough

🧠 Problem:
You find a rock that has layers and contains shell fossils. What type of rock is it, and how did it form?

✅ Solution:

• Fossils and layers → Sedimentary rock.

• Formed from compacted sediments, likely from sea life remains.

✔️ Answer: It is a sedimentary rock formed from sediments with shell fossils.

✍🏽 Practice Exercises

1. Fill in the blanks

(a) Rocks made from cooled magma are called _______ rocks.
(b) _______ rocks form in layers from compressed sediments.
(c) When rocks change due to heat and pressure, they become _______ rocks.

Answers:
(a) igneous
(b) sedimentary
(c) metamorphic

2. Match the Rock Type to Its Feature

Answers:
(i) → B, (ii) → A, (iii) → C

3. Short Answer

Q: Describe one way that a sedimentary rock can become a metamorphic rock.

Sample Answer:
If a sedimentary rock is buried deep in the Earth and exposed to heat and pressure, it can change into a metamorphic rock.

🌀 Recap

Today, we learned:

• Rocks are natural materials made of minerals.

• There are 3 main types of rocks:

  • Igneous (from magma/lava),

  • Sedimentary (from compressed sediments),

  • Metamorphic (changed by heat and pressure).

• Rocks are part of a rock cycle, constantly transforming from one type to another.

• We can identify rock types by their features like layering, crystals, or fossil content.

💭 Reflection Prompt

Take a walk or look outside your window. Do you see a stone, gravel, or hillside?
What kind of rock might it be? Based on what you learned today, describe how that rock might have formed.