Describe the nature and mode of origin of the main types of rock at the earth's crust.

The rocks are generally of three types at crust's: i Igneous Rock ii Sedimentary Rock iii Metamorphic Rock Nature of Rocks: i Igneous → generally made of single ore → low fossil deposits, gets early decomposed ii Metamorphic (Q-Gneiss) → hard & complex due to action of heat & pressure → Rich in fossil depot iii Sedimentary (Q-coal) → Layered Nature, trapping of fossils in layers, Moderate strength Mode of Origin: i Igneous Rock → Volcanic origin, Cooling of magma on earth's crust ii Sedimentary Rock → formed due to deposition of weathered particles, process of lithification to solidify both iii Metamorphic Rock → Action of Heat & pressure on Igneous & Sedimentary Rock, Aes Tough, Rock Cycle Thus, Rock Cycle is process of creation, evolution & destruction

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