Understanding Rocks and Minerals

Oct 5, 2024

Lecture on Rocks and Minerals

Introduction

  • The Earth is a dynamic planet with changes geologically and biologically.
  • Focus on geology in this lecture; geophysics in the next chapter.

Metamorphic Rocks

  • Characterized by ribbon-like layers and folding.
  • Understanding the rock cycle.

Earth's Crust Composition

  • Composed mainly of eight elements, predominantly silicon and oxygen.
  • Iron is more prevalent in the Earth's interior.

Differentiating Rocks and Minerals

  • Minerals: Naturally occurring substances with a uniform crystalline structure; composed of repeating elements.
  • Rocks: Assemblages of minerals; can contain one or multiple types of minerals.

Properties of Minerals

  1. Crystal Structure: Tetrahedral, octagonal, rhombohedron, etc.
  2. Color: Not a reliable identifier due to similarities across different minerals.
  3. Streak: Color left when scratched on porcelain.
  4. Hardness: Measured with the Mohs hardness scale (1 to 10).
  5. Reactivity: Reaction with hydrochloric acid.
  6. Luminescence: Some minerals glow under black light.
  7. Luster: The way they reflect light (glassy, metallic, dull).
  8. Cleavage and Fracture: How they break.
  9. Density: Mass and volume.

Formation of Minerals

  • Result from chemical precipitation as water evaporates.
  • Additional formation occurs when magma cools.

Types of Rocks

  1. Igneous Rocks: Form from cooling magma (e.g., obsidian, basalt, granite).
  2. Sedimentary Rocks: Formed from compaction and cementation of sediments; where fossils can be found.
  3. Metamorphic Rocks: Formed from existing rocks under heat and pressure (e.g., limestone to marble).

Weathering and Erosion

  • Weathering: Chemical, mechanical, and biological processes.
  • Erosion: Transportation of materials by wind, water, etc.

Geophysical Processes

  • Evidence of Earth's internal structure (e.g., seismic waves, magnetism).
  • Lithosphere and asthenosphere.

Seismic Waves

  • P-waves: Faster, travel through solids and liquids.
  • S-waves: Slower, only through solids.

Earth's Layers

  1. Lithosphere: Solid rock layer.
  2. Asthenosphere: Semi-liquid layer.
  3. Mantle: Mostly molten rock.
  4. Core: Divided into liquid outer core and solid inner core.

Rock Cycle

  • Igneous, sedimentary, and metamorphic rocks transform through various processes.
  • Igneous rocks form from cooled magma.
  • Sedimentary rocks form from lithified sediments.
  • Metamorphic rocks form under heat and pressure.

Conclusion

  • Overview of rock types and cycles.
  • Upcoming lab on the rock cycle.
  • For questions, contact the instructor.