Untitled Quiz

Petrology

• Scientific study of rocks, defined as solid mixtures of minerals or organic matter.
• Classification of rocks: igneous, sedimentary, and metamorphic based on their formation process.

Rock Formation and Classification

• Rocks categorized by formation, composition, and texture.
• Igneous rocks form from cooled magma; sedimentary rocks from accumulated sediments; metamorphic rocks from heat and pressure transformations.

The Rock Cycle

• Illustrates the transformation of one type of rock material to another through geological processes.
• Involves interactions between the geosphere, hydrosphere, atmosphere, and biosphere.
• Processes in the rock cycle include weathering, erosion, deposition, compaction, and cementation.

Transformation Processes

• Igneous to Sedimentary: Weathering and erosion lead to sediments being deposited, compacted, and cemented.
• Sedimentary to Metamorphic: Heating and pressure transform sedimentary rocks into metamorphic rocks.
• Metamorphic to Igneous: Cooling and crystallization of magma forms igneous rocks.

Igneous Rocks

• Form when magma cools and solidifies; can occur due to heating, pressure release, or composition change.
• Textural classification:
  • Plutonic (Intrusive): Coarse-grained, cool slowly beneath the surface (e.g., granite).
  • Volcanic (Extrusive): Fine-grained, cool quickly at the surface (e.g., basalt).
• Compositional classification:
  • Mafic: Dark minerals, rich in iron and magnesium.
  • Felsic: Light minerals, rich in aluminum and silica.

Sedimentary Rocks

• Form from weathering, erosion, and deposition of sediments at or near the Earth's surface without heat and pressure.
• Layered structures (strata) due to stratification processes.
• Types include:
  • Clastic: Fragments of rock cemented together (e.g., breccia).
  • Chemical: Minerals crystallized from solution (e.g., limestone).
  • Organic: Derived from accumulated biological materials (e.g., coal).

Metamorphic Rocks

• Form through changes in temperature and pressure, usually deep in the Earth.
• Types of metamorphism:
  • Contact Metamorphism: Heating by nearby magma leads to mineral changes.
  • Regional Metamorphism: Pressure builds in rocks deeper in the Earth due to tectonic activity.
• Textural classification:
  • Foliated: Aligned mineral grains (e.g., gneiss).
  • Non-Foliated: Randomly arranged minerals (e.g., marble).

Key Minerals and Composition

• Hornfels: Fine-grained non-foliated metamorphic rock from contact metamorphism.
• Gneiss: Banded appearance from foliation and typically contains quartz or feldspar.
• Marble: Non-foliated formed from limestone, primarily composed of calcium carbonate.

Rock Identification Examples

• Obsidian: Mafic, fine-grained, extrusive volcanic glass.
• Breccia: Clastic rock with large angular fragments cemented together.
• Coal: Organic sedimentary rock, significant as a fossil fuel.