Chapter: Minerals and Rocks

• Introduction to Minerals

  • Definition: Naturally occurring, inorganic, solid substances with a definite chemical composition and atomic structure.
  • Basic Building Blocks: Rocks are composed of single or multiple minerals.
  • Number of Elements in Earth's Crust: 98% is composed of eight major elements (Oxygen, Silicon, Aluminium, Iron, Calcium, Sodium, Potassium, Magnesium).

• Physical Characteristics of Minerals

  • Crystal Form: External shape determined by internal molecular arrangement.
  • Cleavage: Tendency to break along planes of weak bonding.
  • Fracture: Direction in which a mineral breaks irregularly.
  • Luster: Appearance of a mineral's surface in reflected light (e.g., metallic, silky).
  • Color: Determined by internal molecular structure or impurities.
  • Streak: Color of the mineral's powder when rubbed on porcelain.
  • Transparency: Opaque, translucent, or transparent.
  • Structure: Particular arrangement of individual grains or crystals.
  • Hardness: Resistance to scratching (measured on Mohs' Scale from 1 to 10).
  • Specific Gravity: Ratio of the weight of a mineral to the weight of an equal volume of water.

• Major Groups of Minerals

  • Silicates: Most abundant group (e.g., Quartz, Feldspar, Zeolite, Olivine).
  • Oxides: Combination of oxygen and other elements (e.g., Haematite, Magnetite).
  • Sulphides: Combination of sulphur with metals (e.g., Pyrites, Galena).
  • Sulphates: Presence of sulphate ion (e.g., Gypsum, Barytes).
  • Carbonates: Carbon combined with other elements (e.g., Calcite, Dolomite).
  • Halides: Salts like fluorite, halite.
  • Native Elements: Occur in pure form (e.g., Gold, Silver, Copper, Diamond).

• Rocks

  • Definition: Aggregates of one or more minerals forming the Earth's crust.
  • Petrology: The scientific study of rocks.
  • Classification based on Mode of Formation:
    • Igneous Rocks
      • Formed by cooling and solidification of magma/lava.
      • Parent rocks of all other rocks.
      • Subtypes:
        • Intrusive Igneous Rocks: Cool slowly deep inside crust (e.g., Granite).
        • Extrusive Igneous Rocks: Cool rapidly on the surface (e.g., Basalt, Gabbro).
    • Sedimentary Rocks
      • Formed through lithification (compaction and cementation of sediments).
      • Characterized by layers or strata.
      • Subtypes:
        • Mechanically formed: Sandstone, Conglomerate, Shale.
        • Organically formed: Limestone, Coal.
        • Chemically formed: Chert, Gypsum, Halite.
    • Metamorphic Rocks
      • Formed under the influence of heat, pressure, and solution (Metamorphism).
      • Subtypes:
        • Foliated Rocks: Presence of bands or light/dark stripes (e.g., Gneiss, Schist).
        • Non-foliated Rocks: Lack of banding (e.g., Marble, Quartzite).

• The Rock Cycle

  • Continuous process of transformation between igneous, sedimentary, and metamorphic rocks.
  • Magma cools to form Igneous Rocks.
  • Igneous rocks weather and erode to form Sedimentary Rocks.
  • Igneous and Sedimentary rocks undergo heat and pressure to form Metamorphic Rocks.
  • Rocks melt back into Magma under extreme heat and pressure inside the Earth.