Sedimentary Rocks
* Origin: Formed from existing rocks (igneous, metamorphic, or even other sedimentary rocks) that have been broken down, transported, and deposited in layers.
* Process:
1. Weathering: Rocks are broken down into smaller pieces (sediments) by wind, water, ice, or chemical reactions.
2. Erosion: These sediments are then transported by wind, water, or ice to a new location.
3. Deposition: The sediments settle and accumulate in layers.
4. Compaction: The weight of overlying sediments compresses the lower layers, squeezing out water and air.
5. Cementation: Dissolved minerals in the water precipitate between the sediment grains, binding them together to form solid rock.
* Key Characteristics:
* Layering (strata) is common.
* May contain fossils.
* Often porous and permeable.
* Examples: sandstone, limestone, shale, conglomerate.
Metamorphic Rocks
* Origin: Formed from existing igneous, sedimentary, or even other metamorphic rocks that have been subjected to intense heat and pressure.
* Process:
1. Heat: Heat from the Earth's interior or from the intrusion of magma melts and recrystallizes the existing minerals.
2. Pressure: The weight of overlying rocks or tectonic forces squeeze the rock, causing the minerals to rearrange.
3. Chemical Reactions: The intense heat and pressure can lead to chemical reactions that create new minerals.
* Key Characteristics:
* Often have a banded or foliated texture (layers of minerals).
* May have a glassy or recrystallized appearance.
* Usually harder and denser than the original rock.
* Examples: marble (from limestone), slate (from shale), gneiss (from granite), quartzite (from sandstone).
In Summary:
* Sedimentary rocks are formed from fragments of existing rocks that are cemented together.
* Metamorphic rocks are formed when existing rocks are transformed by heat and pressure without melting completely.
