Igneous rocks
🌋 This Topic is About...
- 🪨 I will learn that rocks come in different types and each has special features.
- 📸 I will use diagrams and photos to help describe igneous rocks.
- 🌋 I will find out how igneous rocks form when magma cools and hardens.
- 🔮 I will make predictions about how rocks form and check if they are right.
- 🧪 I will draw conclusions from my results using what I know about science.
- ⚠️ I will learn how to plan and carry out experiments safely.
- 🔍 I will sort and group rocks by looking at their differences.
- 🗝️ I will complete a key to identify igneous rocks using what I observe.
Let’s become rock detectives! 🧭🪨
🌟 Key Words
- crystal
- crystalline
- extrusive igneous rock
- geologist
- igneous rock
- intrusive igneous rock
- mineral
- naked eye
- sedimentary rock
- solidification
📖 Tap to Learn the Meanings!
- 💎 crystal: A solid substance with flat sides and a regular shape.
- ✨ crystalline: Made up of crystals or having a crystal-like structure.
- 🌋 extrusive igneous rock: Rock formed when lava cools quickly on the Earth’s surface.
- 🧑🔬 geologist: A scientist who studies rocks, minerals, and the Earth’s structure.
- 🪨 igneous rock: Rock formed when hot molten material (magma or lava) cools and hardens.
- 🌋 intrusive igneous rock: Rock formed when magma cools slowly beneath the Earth’s surface.
- 🔸 mineral: A natural solid found in rocks with a definite structure and composition.
- 👀 naked eye: Seeing something without using a microscope or magnifying tool.
- 🪵 sedimentary rock: Rock formed from layers of sand, mud, or other small pieces pressed together.
- ❄️ solidification: The process of a liquid cooling and becoming solid.
Fantastic! You now know the key rock science words! 🪨🔍
🔍 Think Like a Scientist 1: Collect and Sort Rocks
- Find some samples of rock. Make sure you don’t choose ‘manufactured’ materials like concrete and brick. Good places to look are rock cuttings where a road passes through and the rocks are exposed, or a quarry where rock is being cut out to use for building materials. Ask an older sibling or adult to help you.
🛡️ Safety: Be careful not to fall or climb any steep rock faces! ⚠️
- Put a label on each rock with your name and the place where you found the rock. Bring your rock samples to class.
- Work in groups and use a hand lens to study your rocks.
- Investigate your rocks by answering these questions about each rock:
- Does the rock have only one colour or different colours?
- Does the rock consist of grains stuck together?
- Can you see shiny crystals in the rock?
- Divide your rocks into two groups:
- 🪨 Rocks which are one main colour and consist of grains stuck together are called sedimentary rocks. You will find out more about them in the next topic.
- 🌋 Rocks which have shiny crystals and may have several colours and a spotted appearance are called igneous rocks. We will focus on igneous rocks in this topic.
💭 How am I doing?
- Did you manage to find a rock sample?
- Could you see the differences between the rocks everyone collected?
Choose from one of these faces: 😊 😐 😞
🌟 Tap to Reflect
- If you collected rocks safely and observed their colours and grains, you did great! 👏
- Noticing crystals or differences between rocks means you’re thinking like a real geologist! 🧭
Excellent job exploring rocks, young scientist! 🪨🔍
🔥 What Are Igneous Rocks?
The word ‘igneous’ means fire. Igneous rocks come from magma that has cooled into solid rock. Magma is very hot—like a fire.
🌍 Magma Comes From Deep Inside Earth
Look at the diagram. Magma rises from the mantle, deep below Earth’s surface. When magma cools it becomes a solid. This change is called solidification.
🌋 Lava Cools to Make Extrusive Rocks
Some magma reaches the surface as lava. When lava cools, it solidifies into an extrusive igneous rock. ‘Extrusive’ means outside the Earth’s crust, on the surface. A common extrusive rock is black basalt.
🪨 Magma That Stays Inside Makes Intrusive Rocks
Some magma stays within the Earth’s crust. It cools slowly and becomes an intrusive igneous rock. ‘Intrusive’ means inside the crust. A well-known intrusive rock is granite. Over time, when the rocks above wear away, the granite can appear at the surface.
💎 What Are Igneous Rocks Made Of?
All igneous rocks are made of minerals. Each mineral is made from a different group of substances. The most common substances in the Earth’s crust are silica, oxygen, aluminium, magnesium, and iron. These combine in different ways to form minerals.
🔮 Crystals in Igneous Rocks
The most important feature of igneous rocks is that they are crystalline. Crystals form when minerals cool and become solid. Quartz, for example, is a mineral made of silica and oxygen and forms shiny, solid crystals.
🌋 How Crystals Form
When magma is deep below the Earth’s surface, it cools slowly. This slow cooling allows large crystals to form. These crystals can be seen with the naked eye. Because the crystals grow close together, they do not form separate shapes like quartz crystals do when they grow freely.
🪨 Granite and Its Minerals
Granite is an example of an intrusive igneous rock. It has different colours because it contains different minerals such as quartz, feldspar, and mica. These minerals give the rock a speckled look.
🔥 Rocks That Cool Quickly
When lava cools quickly at the surface, it forms an extrusive igneous rock. The crystals in these rocks are too small to see with the naked eye. A common example of this kind of rock is basalt.
🧂 Making Crystal Models
In the next activity, you are going to make salt crystals in both a warm and a cool environment. This models how crystals form in intrusive and extrusive igneous rocks.
🔍 Think Like a Scientist 2: Make Your Own Crystals
🤔 Question: How does temperature affect how crystals form?
🧰 You will need: 2 glass jars, 2 paper clips, 2 pencils, 2 × 10 cm pieces of string, 1 cup of coarse salt, hot water, a teaspoon 🧂💧
🛡️ Safety First:
- Be careful with hot water! 🔥
- Ask an adult to help you pour and handle jars safely. 👩🔬
📝 Method:
- Before beginning, talk about how to stay safe when using very hot water.
- Tie a paper clip to one end of each piece of string.
- Half fill each jar with hot water. Be careful not to burn yourself!
- Add coarse salt to each jar and stir until it dissolves. Keep adding more salt until no more dissolves. Leave jar 1 to cool.
- Lower the paper clip into jar 2. Wind the other end of the string around a pencil and rest the pencil across the top of the jar, as shown in the diagram.
- Leave jar 2 in a warm place for a week. Check and observe daily. Unwind the string if needed so the crystal stays in the salt solution. Crystals will form on the paper clip.
- Once jar 1 has cooled, lower its paper clip into the jar as you did for jar 2. Keep jar 1 in the fridge for a week. Check daily and unwind the string so the crystal stays in the solution.
❓ Questions:
🌟 Tap to Reflect
- Jar 2 in the warm place will form crystals faster but smaller. 🌞
- Jar 1 in the cool fridge will form crystals more slowly but they’ll be larger. ❄️
- This models how extrusive rocks (like basalt) and intrusive rocks (like granite) form. 🪨
Great observation work, young scientist! 👏🔍