The Rock Cycle

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The Rock Cycle & Classification of Rocks

The rock cycle is the formation, breakdown and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes. The rock cycle is an illustration that is used to describe how the three rock types are related and how Earth processes change a rock from one type to another over time. Each group contains a collection of rock types that differ from each other on the basis of the size, shape and arrangement of mineral grains. Due to the driving forces of the rock cycle, plate tectonics and the water cycle, rocks are forced to change as they encounter new environments as they do not remain in equilibrium.


At the Earth’s surface, rocks are broken down; this is caused by rainwater, extremes of temperature, and biological activity. Weathering should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, wind and gravity. There are three types of weathering: physical, chemical and biological. Physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions such as heat, water ice and pressure. Chemical weathering involves rain water combining with mineral grains in rocks to form new minerals. Living organisms such as trees, bacteria, and animals contribute to biological weathering.

Erosion is the removal of soil and rock particles. It usually occurs due to transport by wind, water or ice.

Deposition of sediment
Deposition is the laying down of sediment carried by wind, water, or ice. Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of particle weight and friction which resist motion. Burial and compaction:

Layers of sediments are piled one upon another, so the weight of the layers compacts the sediment grains.

Sedimentary rock
Sedimentary rocks are those formed by other pieces existing rocks,...
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