ROCKS AND MINERALS

 🌍 ROCKS AND MINERALS

Geography – Class 7 CBSE | Chapter 2: Inside Our Earth

WHAT ARE ROCKS?

• A rock is any natural mass of mineral matter that forms part of the Earth's crust.

• Rocks vary in colour, size, and texture.

• The Earth’s crust is completely made up of different types of rocks.

TYPES OF ROCKS

There are three major types of rocks based on how they are formed:

🟥 1. Igneous Rocks – "Primary Rocks"

• Formation: When molten magma cools and solidifies, igneous rocks are formed.

• They are called primary rocks because they are the first rocks formed directly from magma.

• Types of Igneous Rocks:

  🔸 Extrusive Igneous Rocks:

  • Formed when molten lava comes out of a volcano and cools quickly on the Earth’s surface.

  • They have a fine-grained structure due to rapid cooling.

  • Example: Basalt (The Deccan Plateau is made of basalt).

  🔸 Intrusive Igneous Rocks:

  • Formed when magma cools slowly deep inside the Earth’s crust.

  • Slow cooling allows the formation of large crystals or grains.

  • Example: Granite (used to make grinding stones for spices).

🟫 2. Sedimentary Rocks

• Formation:

  • Formed from sediments (small rock particles) that are broken off, transported, and deposited by wind, water, or ice.

  • Over time, these loose sediments are compressed and hardened into layers.

• Features:

  • Often contain fossils – remains of plants, animals, and microorganisms.

• Example: Sandstone (formed from compacted sand grains).

🟪 3. Metamorphic Rocks

• Formation:

  • Formed when igneous or sedimentary rocks are subjected to intense heat and pressure inside the Earth.

  • This leads to a change in form, structure, or composition.

• Examples:

  • Clay → Slate

  • Limestone → Marble

🔄 THE ROCK CYCLE

The Earth’s rocks do not stay the same forever — they are constantly changing from one form to another in a cyclic process known as the Rock Cycle.

🌀 Steps of the Rock Cycle:

1. Molten magma cools → forms Igneous Rocks.

2. Igneous rocks break down into small particles → form Sedimentary Rocks.

3. Igneous or Sedimentary rocks under heat & pressure → become Metamorphic Rocks.

4. Metamorphic rocks may melt → form molten magma again.

5. The cycle repeats.

This cycle shows that rocks are always transforming — no rock type is permanent.

💎 MINERALS

• Definition: Minerals are naturally occurring substances with definite chemical composition and physical properties.

• Rocks are made up of one or more minerals.

✅ USES OF MINERALS

Minerals are extremely valuable to humans:

Use	Examples
Fuels	Coal, petroleum, natural gas
Metals for Industry	Iron, gold, uranium, aluminium
Medicines	Various mineral-based compounds
Fertilizers	Minerals improve soil fertility

🎮 ROCKS IN OUR DAILY LIFE

Rocks are not just for construction – they are also part of traditional games!

• Granite is used in grinding stones.

• Stones are used in games like:

  • Pitthoo (Seven Stones)

  • Stapu/Kit Kit (Hopscotch)

  • Gitti (Five Stones)

Ask your parents or grandparents to know more about such fun traditional games!

📝 SUMMARY TABLE

Type of Rock	How It's Formed	Example	Special Features
Igneous	From cooled magma/lava	Basalt, Granite	Primary rocks, fine or coarse grains
Sedimentary	From compressed sediments	Sandstone	Formed in layers, may contain fossils
Metamorphic	From heat and pressure on other rocks	Slate, Marble	Changed form due to internal forces