Geography Notes Chapter 7 Rocks and Rock Types Class 6 Maharashtra Board

1. What are Rocks?

• Rocks are hard substances that make up the Earth’s crust.
• They are found on land, riverbeds, mountains, and ocean floors.
• Rocks are made of different minerals like silica, aluminium, magnesium, and iron.
• The properties of rocks depend on which minerals they are made of and how they were formed.

2. Types of Rocks

Rocks are divided into three types based on their formation:

1. Igneous Rocks (Primary Rocks)
2. Sedimentary Rocks
3. Metamorphic Rocks

1) Igneous Rocks (Primary Rocks)

• These rocks are formed when hot magma (inside the Earth) or lava (on the surface) cools and hardens.
• They are called primary rocks because they were the first rocks to form on Earth.

Characteristics of Igneous Rocks:

• • Hard and heavy
  • No fossils
  • Homogeneous (uniform structure)

Examples:

1. Basalt → Found in the Sahyadri Hills and Maharashtra Plateau
2. Granite → Used for making buildings
3. Pumice → A light, porous rock that can float on water

2) Sedimentary Rocks

• These rocks are formed when small rock particles (sand, mud, pebbles) are carried by rivers, wind, or glaciers and settle in layers.
• Over time, the pressure of the upper layers turns these sediments into rocks.
• Fossils of dead plants and animals are often found in these rocks.

Characteristics of Sedimentary Rocks:

• Layered structure
• Brittle and light
• Porous (can absorb water)

Examples:

1. Sandstone → Used for making buildings (Red Fort in Delhi is made of sandstone)
2. Limestone → Used for making cement
3. Coal → Used as fuel
4. Shale → Used for making bricks

3) Metamorphic Rocks

• These rocks are formed when igneous or sedimentary rocks change due to high heat and pressure inside the Earth.
• The minerals in the rocks get rearranged, making them harder and shinier.
• These rocks do not contain fossils.

Characteristics of Metamorphic Rocks:

• Hard and durable
• Shiny or crystal-like appearance
• No fossils

Examples:

1. Marble → Formed from limestone (Used in Taj Mahal)
2. Diamond → Formed from coal (Very expensive)
3. Slate → Formed from shale (Used for making tiles)
4. Quartzite → Formed from sandstone

4. How are Fossils Formed?

• Fossils are the preserved remains or impressions of dead plants and animals found in sedimentary rocks.
• Over time, layers of rock cover dead organisms, and their shape gets preserved.
• Fossils help us understand the history of life on Earth.

Example:

• Dinosaur fossils have been found in sedimentary rocks.

5. Distribution of Rocks in Maharashtra

• Basalt is found in most parts of Maharashtra due to ancient volcanic eruptions.
• Laterite rocks are common in Konkan regions like Ratnagiri and Sindhudurg.

6. Importance of Rocks

1. Construction → Rocks like granite, sandstone, and limestone are used in buildings, roads, and bridges.
2. Energy → Coal is used as fuel to generate electricity.
3. Jewelry → Diamonds, gold, and gemstones are obtained from rocks.
4. Tools and Machinery → Some rocks are used to make cutting tools and equipment.
5. Soil Formation → Weathered rocks break down to form soil.

7. Difference Between Igneous, Sedimentary, and Metamorphic Rocks