🪨

Understanding Minerals and Their Structures

Feb 27, 2025

Lecture Notes: Minerals and Their Composition

Overview of Mineral Composition

  • Minerals are grouped based on their compositions.
  • Silicate Minerals
    • Largest group of rock-forming minerals on Earth.
    • Contain silicon and oxygen, making up about 90% of Earth's crust.
    • Most abundant silicate minerals: Feldspars and Quartz.
      • Feldspars: Plagioclase feldspar, Potassium feldspar (also known as Orthoclase feldspar).
    • Only about 8% of the crust's minerals are non-silicate minerals.

Formation and Structure of Silicate Minerals

  • Formed by igneous processes:
    • Cooling of magma underground.
    • Cooling of lava on Earth's surface.
  • Silicate Tetrahedron
    • Structure: One silicon ion surrounded by four oxygen ions.
    • Covalent bonds between oxygen ions and silicon ion.
    • Extremely strong bonds.

Silicate Mineral Groups

  • Grouped based on the orientation of silicate tetrahedra:
    • Single Tetrahedra: Example - Olivine.
    • Chains of Tetrahedra: Example - Agite.
    • Double Chains, Sheets: Examples - Mica minerals like Biotite and Muscovite.
    • 3-Dimensional Framework: Examples - Quartz, Feldspar.
  • Key point: All silicate minerals contain silicate tetrahedra arranged in different orientations.

Other Mineral Classes

  • Carbonates
    • Example: Calcite (contains carbonate anion).
    • Second most common mineral type in the crust.
  • Oxides
    • Metal atoms bonded with oxygen, e.g., iron oxide (rust).
  • Halides: Example - Fluorite.
  • Sulfides: Example - Pyrite (fool's gold).
  • Sulfates, Phosphates
  • Native Elements
    • Minerals composed of one type of element, e.g., copper, gold, silver, platinum.
    • Include polymorphs graphite and diamond (pure carbon).
    • Tend to be rare, especially precious metals.

Common Rock-Forming Minerals

  • Over 5,000 named minerals, but less than a dozen are very common.
  • Seven Most Common Rock-Forming Minerals:
    • Silicates: Feldspars (two types), Quartz, Amphibole, Biotite, Olivine, Pyroxene.
    • Carbonate: Calcite (forms limestone).
  • Note: Olivine and Pyroxene are significant in Earth's mantle.

Full transcript