Igneous Rocks

• "Igneous" means "fire-formed" (from Latin "ignis" = fire).
• How they are made:
• Formed from molten rock called magma.
• Magma is hot, liquid rock underneath the Earth's crust.
• When magma cools down and becomes solid (solidifies), it forms igneous rocks.
• Characteristics of Igneous Rocks:
• Crystalline Structure: Made of crystals that are usually tightly packed together. Think of salt or sugar crystals.
• No Layers (Strata): They don't form in layers like some other rocks. They are more like solid masses.
• No Fossils: Usually no fossils inside because the magma is too hot to preserve them.
• Two Main Types of Igneous Rocks (based on where they cool):
• Plutonic Rocks (Intrusive):
• Formed: Deep inside the Earth's crust.
• Cooling: Cool down very slowly because they are insulated by surrounding rock.
• Crystals: Slow cooling allows large crystals to grow. You can often see them easily.
• Examples: Granite, diorite, gabbro.
• How we see them: They are brought to the surface over millions of years by denudation and erosion (wearing away of the land).
• Volcanic Rocks (Extrusive):
• Formed: When molten rock (lava) is poured out of volcanoes onto the Earth's surface.
• Cooling: Cool down very quickly because they are exposed to air or water on the surface.
• Crystals: Fast cooling makes small crystals (or sometimes almost no crystals). Often harder to see individual crystals.
• Example: Basalt is a common volcanic rock.
• Basalt Forms:
• Lava flows: Rivers of lava that spread out.
• Lava sheets: Wide, flat layers of lava.
• Lava plateaus: Large, high, flat areas made of lava (e.g., Deccan Plateau in India, Columbia-Snake Plateau in USA, Antrim Plateau in Northern Ireland).
• Columnar Basalt: Some basalt cools in a special way to make long, column-like shapes (polygonal columns). Example: Giant's Causeway in Northern Ireland is famous for this.
• Dykes and Sills: Sometimes magma pushes up through cracks (clefts) in the Earth and solidifies:
• Dykes: Vertical, wall-like formations.
• Sills: Horizontal, sheet-like formations.
• Properties and Uses of Igneous Rocks:
• Very Hard and Resistant: They are strong and don't wear away easily.
• Uses:
• Road-making: Crushed igneous rocks are used for roads.
• Monuments & Gravestones: Polished igneous rocks (like granite) are used for statues, memorials, and tombstones because they last a long time.

In Simple Words: Igneous rocks are "fire rocks" made from cooled magma or lava. They are usually hard, crystalline, and don't have layers or fossils. There are two main types: plutonic (cooled slowly deep inside, big crystals like granite) and volcanic (cooled quickly on the surface, small crystals like basalt). We use igneous rocks for roads and monuments because they are strong.