JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year GENERAL GEOLOGY Previous Question Paper (August - 2022 - R18)

Rocks are classified into three primary types based on their mode of formation:

1. Igneous Rocks: Formed by the cooling and solidification of molten rock (magma or lava). These are classified as intrusive (plutonic), which cool slowly beneath the surface resulting in coarse grains, or extrusive (volcanic), which cool rapidly on the surface resulting in fine grains. Examples include granite and basalt.
2. Sedimentary Rocks: Formed by the accumulation, compaction, and cementation of mineral particles or organic matter (lithification) over long periods. These often exhibit layering (stratification) and may contain fossils. Examples include sandstone, limestone, and shale.
3. Metamorphic Rocks: Formed from pre-existing igneous or sedimentary rocks that undergo physical or chemical changes due to intense heat, pressure, or chemically active fluids without melting. This process is known as metamorphism. Examples include marble (from limestone) and slate (from shale).

Weathering is the breakdown of rocks at the Earth's surface into smaller fragments or chemical components through three main processes:

1. Physical (Mechanical) Weathering: The disintegration of rocks without chemical change. Key mechanisms include frost wedging (water freezing in cracks and expanding), thermal expansion (repeated heating and cooling causing stress), and exfoliation (pressure release causing outer layers to peel off).
2. Chemical Weathering: The decomposition of rocks through chemical reactions that alter their mineral composition. Major processes include oxidation (reaction with oxygen, common in iron-bearing minerals), carbonation (reaction with carbonic acid, effective on limestone), and hydrolysis (reaction with water to form clay minerals).
3. Biological Weathering: The breakdown of rocks caused by living organisms. This includes physical pressure from plant roots growing into fractures and chemical weathering caused by organic acids released by bacteria, fungi, and lichens that dissolve rock minerals.