1. Weathering and Erosion:
* Weathering: Igneous rocks exposed at the Earth's surface are broken down by physical and chemical processes:
* Physical weathering: Freezing/thawing, wind abrasion, and plant roots can break the rock into smaller pieces.
* Chemical weathering: Rainwater (slightly acidic) reacts with minerals in the rock, dissolving and altering them.
* Erosion: Once broken down, the fragments are transported by wind, water, or ice to a new location.
2. Deposition:
* The eroded fragments (sediments) settle in a new location, often in layers.
* This location might be a lake, riverbed, ocean floor, or even a desert.
* The sediments are deposited in layers, with heavier particles settling first.
3. Burial and Compaction:
* Over time, more sediments are deposited on top, burying the earlier layers.
* The weight of the overlying layers compresses the sediments, squeezing out water and air, and compacting the layers.
4. Cementation:
* Dissolved minerals in groundwater seep through the compacted sediment layers.
* These minerals crystallize and bind the sediment particles together, forming a solid rock.
* This process is called cementation.
5. Formation of Sedimentary Rock:
* The compacted and cemented sediments become a sedimentary rock.
* The type of sedimentary rock depends on the original sediments and the cementing minerals.
* Examples include sandstone (from sand grains), limestone (from calcium carbonate shells), and shale (from clay particles).
Important Note:
* This process is very slow and takes millions of years.
* The sedimentary rock formed from the igneous rock may contain fragments of the original igneous rock, giving clues to its origin.
In summary:
The transformation from igneous to sedimentary rock is a cycle driven by:
* Breakdown: Weathering and erosion break the igneous rock into fragments.
* Transport: Sediments are transported away from their source.
* Burial: The sediments are buried under more sediment layers.
* Compaction: The weight compresses the sediments.
* Cementation: Minerals bind the sediment particles together, forming the sedimentary rock.
