Geology: Types of Rocks

Igneous Rocks

• Formed from the cooling and solidification of magma or lava
• Can be either intrusive (formed below the Earth's surface) or extrusive (formed above the Earth's surface)
• Characteristics:
  • Coarse-grained texture (intrusive)
  • Fine-grained texture (extrusive)
  • May contain gas bubbles or minerals
• Examples: granite, basalt, obsidian

Sedimentary Rocks

• Formed from the accumulation and compression of mineral or organic particles
• Can be formed through:
  • Mechanical weathering (erosion and deposition)
  • Chemical weathering (chemical reactions)
  • Organic activity (shell formation, etc.)
• Characteristics:
  • Layered or bedded structure
  • May contain fossils or other inclusions
• Examples: shale, limestone, sandstone

Metamorphic Rocks

• Formed from the alteration of existing rocks under high pressure and temperature conditions
• Can be formed through:
  • Mountain-building processes
  • Tectonic plate movement
• Characteristics:
  • Foliated (banded or layered) or non-foliated texture
  • May exhibit mineral changes or new mineral formation
• Examples: marble, slate, quartzite

Rock Cycle

• The continuous process by which rocks are formed, transformed, and destroyed
• Involves the three main types of rocks (igneous, sedimentary, metamorphic) and their interactions
• Processes involved:
  • Magmatic differentiation (igneous formation)
  • Weathering and erosion (sedimentary formation)
  • Metamorphism (metamorphic formation)
  • Melting and cooling (igneous formation)

Rocks Classification in India

• The Geological Survey of India (GSI) classifies rocks into four categories:
  1. Archaean (>2500 Ma)
  2. Proterozoic (2500-541 Ma)
  3. Phanerozoic (541 Ma-present)
• Classification is based on age, composition, and tectonic setting
• Important rock formations in India include:
  • The Indian Shield ( ancient cratons and mobile belts)
  • The Himalayan Orogen ( collisional mountain-building)

Igneous Rocks

• Formed from cooling and solidification of magma or lava
• Can be either intrusive (formed below Earth's surface) or extrusive (formed above Earth's surface)
• Characteristics:
  • Coarse-grained texture (intrusive)
  • Fine-grained texture (extrusive)
  • May contain gas bubbles or minerals
• Examples: granite, basalt, obsidian

Sedimentary Rocks

• Formed from accumulation and compression of mineral or organic particles
• Can be formed through:
  • Mechanical weathering (erosion and deposition)
  • Chemical weathering (chemical reactions)
  • Organic activity (shell formation, etc.)
• Characteristics:
  • Layered or bedded structure
  • May contain fossils or other inclusions
• Examples: shale, limestone, sandstone

Metamorphic Rocks

• Formed from alteration of existing rocks under high pressure and temperature conditions
• Can be formed through:
  • Mountain-building processes
  • Tectonic plate movement
• Characteristics:
  • Foliated (banded or layered) or non-foliated texture
  • May exhibit mineral changes or new mineral formation
• Examples: marble, slate, quartzite

Rock Cycle

• Continuous process by which rocks are formed, transformed, and destroyed
• Involves the three main types of rocks (igneous, sedimentary, metamorphic) and their interactions
• Processes involved:
  • Magmatic differentiation (igneous formation)
  • Weathering and erosion (sedimentary formation)
  • Metamorphism (metamorphic formation)
  • Melting and cooling (igneous formation)

Rocks Classification in India

• The Geological Survey of India (GSI) classifies rocks into four categories based on:
  • Age
  • Composition
  • Tectonic setting
• Important rock formations in India include:
  • The Indian Shield (ancient cratons and mobile belts)
  • The Himalayan Orogen (collisional mountain-building)
• Time periods for rock classification:
  • Archaean (>2500 Ma)
  • Proterozoic (2500-541 Ma)
  • Phanerozoic (541 Ma-present)

Quiz about the characteristics and formation of igneous and sedimentary rocks, including their textures and examples.