DIFFERENT TYPES OF ROCKS
• Many of the materials we use everyday are made from different kinds of rocks.
• Depending on the way they are formed, rocks are grouped as:
• All rocks on Earth were initially igneous in nature.
Figure 6: Igneous rocks
• The Earth's core is made of molten rock.
• When a volcano erupts, this molten rock flows out.
• It later cools and solidifies to form igneous rock. Inside the Earth, molten rock is called magma and when it flows out onto the surface, it is called lava.
Figure 7: (a) Magma (b) Lava
• Almost 95% of the Earth's crust is made up of igneous rocks.
• These contain minerals such as mica, feldspar, and magnesium.
Figure 8: Granite- A hard igneous rock
Figure 9: Obsidian- Smooth and glassy igneous rock
Figure 10: Pumice- A porous igneous rock
• These rocks are formed by the deposition of the material present at the Earth’s surface.
Figure 11: Sedimentary rocks
• Rain, wind, rivers flowing down mountains, etc., wear down rocks on mountains.
• These small bits of rocks are then carried down and deposited elsewhere.
• Repeated deposition presses down the lower layers and hardens them into rock.
• Such rocks are called sedimentary rocks.
• These rocks are used in the construction of roads; houses; tunnels; canals; etc.
Figure 12: Road and houses made up of rocks
Figure 13: Limestone- A soft sedimentary rock
Figure 14: (a) Sandstone- A soft stone made up of sedimentary rock
(b) Red Fort, Delhi- made up of red sandstone
Figure 15: Conglomerate- A cemented sedimentary rock
Figure 16: Shale- A solidified clay
POINT TO REMEMBER:
Many sedimentary rocks have fossils in them because, along with the bits of rocks, animal and plant remains also get deposited during rock formation.
• These rocks are a combination of rock types; compressed together by high pressure which gives them a more hard texture than the other types of rocks.
Figure 17: Combination of rock types- Metamorphic rocks
• They are the rocks that have changed their form to metamorphose.
Figure 18: Different types of metamorphic rocks
Figure 19: Marble- A changed sedimentary rock
Figure 20: Taj Mahal
Figure 21: Slate- Formed from shale
Figure 22: Gneiss- Formed from granite
Figure 23: Quartzite- Formed from sandstone