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

(i) Igneous Rock (ii) Sedimentary Rock (iii) Metamorphic Rock

Nature of Rocks

1. Igneous → generally made of single one → low fossil deposits → gets easily decomposed

2. Metamorphic → hard & complex due to action of heat & pressure (eg) - gneis → Rich in fossil deposit Relatively stable nature

3. Sedimentary → Layered Nature (eg) - Coal → Trapping of fossils in layers Moderate strength

Mode of origin

1. Igneous Rock → Volcanic origin → cooling of magma on earth's crust

1. Sedimentary Rock → formed due to deposition of weathered particles → process of lithification to solidify rock

2. Metamorphic Rock → Action of Heat & pressure on igneous & sedimentary rock → Are Tough