Igneous Rocks

Key Notes:

Formation of Igneous Rocks:

• Igneous rocks are formed from the cooling and solidification of molten rock, known as magma (inside the Earth) or lava (when it reaches the surface).

Types of Igneous Rocks:

• Intrusive (Plutonic) Igneous Rocks: Form when magma cools slowly beneath the Earth’s surface, resulting in large crystals (e.g., granite).
• Extrusive (Volcanic) Igneous Rocks: Form when lava cools quickly on the Earth’s surface, resulting in small or no crystals (e.g., basalt).

Characteristics of Igneous Rocks:

• They are typically hard and dense.
• They can be glassy or grainy in texture depending on how fast they cool.
• They contain minerals such as quartz, feldspar, and mica.

Examples of Igneous Rocks:

• Granite: An intrusive igneous rock that has large, visible crystals and is commonly used in construction.

• Basalt: An extrusive igneous rock that forms from lava flows and is the most common rock on the ocean floor.

• Pumice: A light, porous extrusive rock that can float on water due to trapped gas bubbles during formation.

Uses of Igneous Rocks:

• Granite is used for building and monuments due to its durability.
• Pumice is used in personal care products (like exfoliants) and in polishing.

Role in Earth’s Structure:

• Igneous rocks are a major component of the Earth’s crust, forming both continental and oceanic plates.