Lecture Notes: Formation of Rocks

Introduction

• Rocks are classified based on their formation.
• Understanding rock formation provides insight into the rock's characteristics and classification.

Types of Rocks

Igneous Rocks

• Origin of the Name: Derived from the Greek word "ignis," meaning fire.
  • Associated with fire due to volcanic origin (magma/lava).
• Formation Process:
  • Formed from molten rock (magma or lava) that cools and hardens.
  • Magma: Molten material below the Earth's crust.
  • Lava: Molten material above the Earth's crust.
• Types:
  • Intrusive Igneous Rocks: Cool and harden below the Earth's crust.
  • Extrusive Igneous Rocks: Cool and harden above the Earth's crust.

Sedimentary Rocks

• Root Word: "Sediments"—small particles that can form rocks.
• Formation Process:
  • Formed from compacted sediments often found near water sources (rivers, oceans).
  • Water presence aids in compacting the sediments into layers.
  • Layers are formed over time as different sediments accumulate.
• Examples: Limestone, Sandstone.

Metamorphic Rocks

• Origin of the Name: Comes from "morph," meaning change.
• Formation Process:
  • Formed through change in structure/composition due to pressure and heat.
  • Existing rocks (igneous or sedimentary) undergo transformation.

The Rock Cycle

• Concept: Continuous cycle where rocks change form and recycle over time.
• Sequence:
  • Start: Igneous rock forms from molten materials.
  • Erosion: Igneous rocks erode to form sediments.
  • Sedimentation: Sediments compact to form sedimentary rocks.
  • Metamorphosis: Sedimentary rocks transform under pressure/heat into metamorphic rocks.
  • Melting: Metamorphic rocks melt to form igneous rocks.
• Interactions:
  • Metamorphic rocks can also erode into sediments.
  • Both igneous and metamorphic rocks can undergo weathering and erosion to become sediments.
  • Processes:
    • Compaction/Cementation: Sediments to sedimentary rocks.
    • Metamorphosis: Sedimentary to metamorphic rocks due to pressure/heat.
    • Crystallization: Cooling of molten material to form igneous rocks.

Conclusion

• Understanding the rock cycle and formation types is essential for geology.
• Future topics include weathering, which also affects rock formation and features.