1. Igneous Rocks:
* Formation: Igneous rocks form from the cooling and solidification of molten rock, called magma (underground) or lava (above ground).
* Types:
* Intrusive (Plutonic): Formed when magma cools slowly underground, resulting in large crystals. Examples: granite, gabbro.
* Extrusive (Volcanic): Formed when lava cools quickly on the Earth's surface, leading to smaller crystals. Examples: basalt, obsidian.
2. Sedimentary Rocks:
* Formation: Sedimentary rocks form from the accumulation, compaction, and cementation of sediments, which are fragments of pre-existing rocks, minerals, and organic materials.
* Types:
* Clastic: Formed from fragments of other rocks. Examples: sandstone, shale, conglomerate.
* Chemical: Formed from the precipitation of minerals from water solutions. Examples: limestone, rock salt, gypsum.
* Organic: Formed from the accumulation and compaction of organic matter. Examples: coal, oil shale.
3. Metamorphic Rocks:
* Formation: Metamorphic rocks form when existing igneous, sedimentary, or even other metamorphic rocks are subjected to intense heat and pressure, causing their mineral composition and texture to change without melting.
* Types:
* Foliated: Rocks with a layered or banded appearance due to pressure. Examples: slate, schist, gneiss.
* Non-foliated: Rocks with a more uniform texture. Examples: marble, quartzite.
The Rock Cycle:
These three rock types are interconnected through the Rock Cycle, a continuous process where rocks transform from one type to another. The cycle is driven by Earth's internal and external processes:
* Igneous rocks can be weathered and eroded into sediments, which form sedimentary rocks.
* Igneous and sedimentary rocks can be buried deep underground and subjected to heat and pressure, transforming them into metamorphic rocks.
* Metamorphic rocks can melt and solidify to form new igneous rocks, or can be uplifted and weathered to form new sediments.
This constant cycle ensures a dynamic and ever-changing Earth's crust!
