Lithosphere and Rock Formation

Lithosphere Definition

  • Derived from the Greek word "lithos" meaning rock.
  • The solid outer layer of Earth, consisting of:
    • Earth's crust (the "skin" of rock).
    • The upper part of the upper mantle (cool, dense, and rigid).
  • Thickness: extends from Earth's surface to about 44-62 mi (70-100 km).

Layers of the Earth

  • Crust: Thin outermost layer (0.6% of Earth's volume).
    • Thinner under oceans (6-11 km); thicker (25-90 km) for continental crust.
  • Mantle: Makes up over 80% of Earth's volume, primarily made of magnesium, iron, and silicon oxides.
    • Upper Mantle: Rigid and part of the lithosphere.
    • Lower Mantle: Flows slowly, ~few cm per year.
  • Core: Comprises 1/3 of Earth's mass with two parts:
    • Inner Core: Solid, ~1,250 km thick, primarily iron with nickel/cobalt.
    • Outer Core: Liquid, ~2,200 km thick, primarily iron, generating Earth's magnetic field.

Types of Crust

  • Continental Crust:
    • Made up of Felsic rocks (granite).
    • Lighter minerals like quartz and k-feldspar; high silica content but lower Fe/Mg content.
  • Oceanic Crust:
    • Comprised of Mafic rocks (basalt).
    • Darker minerals like olivine; lower silica but higher Fe/Mg.

Plate Boundaries

  • Plate Boundary: Location where two tectonic plates meet.
    • Transform Boundaries: Plates slide past each other (sinistral or dextral).
    • Divergent Boundaries: Plates move apart.
    • Convergent Boundaries: Plates move together, forming subduction zones or causing continental collisions.

Rock Types

  • Igneous Rocks: Formed from cooling and solidification of magma.
    • Plutonic (Intrusive): Cools slowly within Earth. Example: granite.
    • Volcanic (Extrusive): Cools quickly at Earth's surface. Example: basalt, rhyolite.
  • Sedimentary Rocks: Formed by deposition at Earth's surface.
    • Clastic: Fragments of other rocks. Example: sandstone.
    • Chemical: Minerals from solutions. Example: limestone.
    • Organic: From remains of organisms. Example: coal.
  • Metamorphic Rocks: Altered under heat and pressure. Example: marble.

Minerals

  • Naturally occurring solid with specific physical/chemical properties.
  • Composed primarily of silicates (O2 and Si combined with metals like Al, Fe, Ca).
  • Categories of Minerals:
    • Silicious: Contain silicon (e.g., quartz).
    • Non-metallic: Used in industry, break easily (e.g., sulfur).
    • Metal Ore: Valuable for mining (e.g., copper).
    • Gem Minerals: Used for jewelry (e.g., diamond).

Common Rock-forming Minerals

  1. Quartz: Transparent, varies in color (hard).
  2. Feldspar: Light-colored, dull to opaque.
  3. Mica: Cleaves into thin sheets (muscovite and biotite).
  4. Pyroxene: Dark green to black (augite).
  5. Amphibole: Similar to pyroxene, longer, shinier (hornblende).
  6. Olivine: Yellow-green, not well-developed crystals.

Properties of Minerals

  • Color: Easiest but tricky to identify.
  • Luster: Reflection of light (metallic or non-metallic).
    • Types: vitreous, resinous, pearly, greasy, silky, adamantine.
  • Density: Weight and arrangement of atoms (specific gravity).
  • Hardness: Resistance to scratching, measured by Mohs scale (1-10 from talc to diamond).
  • Cleavage/Fracture: Smoothness of breakage; good cleavage vs. jagged fracture.