Types of Rocks
🔹 1. Classification of Rocks
Rocks are generally classified into three main types based on their origin and formation process:
| Rock Type | Formation Process | Key Features |
|---|---|---|
| Igneous | Cooling & solidification of magma/lava | Hard, crystalline, durable |
| Sedimentary | Compaction & cementation of sediments | Layered, fossil-rich, softer |
| Metamorphic | Transformation by heat & pressure | Banded, dense, strong |
🔹 2. Igneous Rocks (Fire Rocks)
Formed when molten rock (magma or lava) cools and solidifies.
| Rock Name | Texture | Type | Characteristics |
|---|---|---|---|
| Granite | Coarse-grained | Intrusive | Strong, used in construction |
| Basalt | Fine-grained | Extrusive | Dark, dense, road metal |
| Pumice | Vesicular | Extrusive | Light, floats in water |
| Obsidian | Glassy | Extrusive | Sharp, black volcanic glass |
| Diorite | Mixed | Intrusive | Salt-pepper appearance |
| Andesite | Fine to medium | Extrusive | Intermediate composition |
🔹 3. Sedimentary Rocks (Layered Rocks)
Formed by deposition and cementation of mineral particles or organic materials.
| Rock Name | Type | Characteristics |
|---|---|---|
| Sandstone | Clastic | Made of sand grains, porous |
| Limestone | Organic/Chemical | Rich in calcium, fossils present |
| Shale | Clastic | Thin layers, made from clay |
| Conglomerate | Clastic | Rounded pebble fragments |
| Breccia | Clastic | Angular rock fragments |
| Coal | Organic | Made from dead plant matter |
🔹 4. Metamorphic Rocks (Changed Rocks)
Formed by alteration of existing rocks under heat and pressure.
| Rock Name | Parent Rock | Characteristics |
|---|---|---|
| Marble | Limestone | Non-foliated, used in sculpture/flooring |
| Slate | Shale | Fine-grained, splits in layers |
| Schist | Shale/Slate | Shiny, foliated, visible minerals |
| Gneiss | Granite | Banded appearance, hard |
| Quartzite | Sandstone | Very hard, used in road construction |
🔸 Quick Summary Table
| Rock Type | Examples | Main Use |
|---|---|---|
| Igneous | Granite, Basalt, Pumice | Construction, roads |
| Sedimentary | Sandstone, Limestone, Shale | Cement, building stone |
| Metamorphic | Marble, Slate, Gneiss | Decoration, tiles, roofing |
📌 Note:
- Igneous = Fire-formed
- Sedimentary = Water-formed
- Metamorphic = Heat & pressure changed
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