Lecture: Minerals and Rocks

What is a Mineral?

• Definition: Inorganic, naturally occurring solid with a definite chemical composition and atomic structure.
  • Inorganic: Not living, never was living.
  • Naturally Occurring: Not man-made.
  • Solid: At standard surface conditions.
  • Definite Chemical Composition: Unique elemental makeup.
  • Specific Atomic Structure.

Common Minerals

• Examples:
  • Potassium Feldspar (Orthoclase)
  • Sulfur
  • Muscovite Mica
  • Galena
  • Calcite
  • Olivine
  • Quartz

Mineral Identification

• Characteristics:
  • Color: Can vary; not reliable except for some (e.g., sulfur is yellow).
  • Hardness: Measured using Mohs scale (1 = softest, 10 = hardest).
    • Test using a glass scratch test (glass hardness = 5.5).
  • Luster: Metallic or non-metallic.
  • Streak: Color of the mineral in powdered form, tested with a streak plate.
  • Breakage:
    • Cleavage: Predictable breaking pattern.
    • Fracture: Random breaking pattern.
  • Other Characteristics: Magnetism, taste, odor, reaction to acid, UV light glow.

Rocks and their Classifications

• Formation: Minerals combine to form rocks.
• Types of Rocks:
  • Igneous Rocks: Form from cooling and solidification of magma or lava.
  • Sedimentary Rocks: Form from compacted sediments.
  • Metamorphic Rocks: Formed under intense heat and pressure.

Igneous Rocks

• Types:
  • Extrusive (Volcanic): Lava cools quickly on the Earth's surface, forming fine-textured rocks (e.g., Basalt, Rhyolite).
    • Glassy Rocks: Obsidian (non-crystalline).
    • Vesicular Rocks: Pumice (contains air bubbles).
  • Intrusive: Magma cools slowly underground, forming coarse-textured rocks (e.g., Granite, Pegmatite).
• Characteristics:
  • Color and Density:
    • Lighter colors and less dense (left side of the chart).
    • Darker colors and more dense (right side).
  • Composition:
    • Felsic: Rich in Silicon and Aluminum.
    • Mafic: Rich in Iron and Magnesium.
• Rock Cycle: Form from melting into magma and solidification.

Sedimentary Rocks

• Formation: Compaction and cementation of sediments.
• Types:
  • Clastic: Made of compacted and cemented sediments (e.g., Conglomerate, Breccia, Sandstone, Siltstone, Shale).
  • Crystalline: Formed from evaporation of minerals in water (e.g., Rock Salt).
  • Bioclastic: Formed from organic matter (e.g., Limestone, Bituminous Coal).
• Rock Cycle: Weathering, erosion, deposition, compaction, and cementation.

Metamorphic Rocks

• Formation: Intense heat and/or pressure.
• Types:
  • Foliated: Formed from regional metamorphism (e.g., Shale → Slate → Phyllite → Schist → Gneiss).
  • Non-foliated: Formed from contact metamorphism or a combination of heat and pressure (e.g., Anthracite Coal, Quartzite, Marble).
• Characteristics:
  • Foliation: Mineral alignment or banding (unique to metamorphic rocks).
  • Processes:
    • Regional Metamorphism: Pressure-dominant.
    • Contact Metamorphism: Heat-dominant.
• Rock Cycle: Change into other types of rocks under heat and pressure.

The Rock Cycle

• Rocks continuously change from one type to another through processes like weathering, melting, and exposure to heat and pressure.
• Example Flow:
  • Igneous → Weathering → Sediments → Sedimentary → Metamorphism → Metamorphic → Melting → Igneous.

Remember, rocks and minerals are fundamental Earth materials that undergo continual transformation through geological processes.