Mineralogy and Petrology

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Mineralogy and Petrology

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Mineralogy and Petrology
 
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1. Classification of Minerals and Their Properties

What Are Minerals?

Minerals are naturally occurring inorganic substances with a definite chemical composition and crystalline structure. Classification of MineralsMinerals are classified based on their chemical composition into the following groups:1. Silicate Minerals (Most Abundant - 90% of Earth’s Crust)
  • Contain silicon (Si) and oxygen (O), often combined with metals.
  • Form the building blocks of rocks.
  • Examples: Quartz (SiO₂), Feldspar, Mica, and Olivine.
2. Non-Silicate Minerals (Less Common but Economically Important)Divided into several groups:
  1. Native Elements: Pure single elements.
    • Example: Gold (Au), Silver (Ag), Diamond (C), Graphite (C).
  2. Oxides: Minerals with oxygen bonded to metals.
    • Example: Hematite (Fe₂O₃), Magnetite (Fe₃O₄).
  3. Sulfides: Contain sulfur and a metal.
    • Example: Pyrite (FeS₂), Galena (PbS).
  4. Carbonates: Contain carbonate (CO₃²⁻).
    • Example: Calcite (CaCO₃), Dolomite.
  5. Sulphates: Contain sulfate (SO₄²⁻).
    • Example: Gypsum (CaSO₄·2H₂O).
  6. Halides: Contain halogen elements (Cl, F, Br).
    • Example: Halite (NaCl), Fluorite (CaF₂).
  7. Phosphates: Contain phosphate (PO₄³⁻).
    • Example: Apatite (Ca₅(PO₄)₃(F,Cl,OH)).
Properties of Minerals

Minerals are identified based on their physical and chemical properties:
  1. Color: The visible color of a mineral. (Least reliable for identification).
  2. Streak: The color of the mineral’s powdered form.
  3. Luster: The way a mineral reflects light (e.g., metallic, glassy, dull).
  4. Hardness: Measured using Mohs Hardness Scale (from 1 to 10).
    • Example: Talc (1) is the softest; Diamond (10) is the hardest.
  5. Cleavage and Fracture:
    • Cleavage: The tendency to break along flat planes.
    • Fracture: Irregular breakage (e.g., Quartz has a conchoidal fracture).
  6. Specific Gravity: Density of the mineral compared to water.
  7. Magnetism: Some minerals (e.g., Magnetite) are magnetic.
  8. Reaction with Acid: Carbonates like Calcite react with HCl by fizzing.
📌 Key Point: Silicate minerals dominate Earth's crust, while non-silicates are important for industrial use.

3. Igneous, Sedimentary, and Metamorphic Rocks

Rocks are naturally occurring aggregates of minerals and are classified based on their formation into three types.1. Igneous Rocks (Formed from Cooled Magma or Lava)
  • Formed when molten rock (magma or lava) cools and solidifies.
  • Intrusive (Plutonic) Igneous Rocks: Formed inside the Earth, cool slowly, have large crystals.
    • Example: Granite, Diorite, Gabbro.
  • Extrusive (Volcanic) Igneous Rocks: Formed on the surface, cool quickly, have small or no crystals.
    • Example: Basalt, Rhyolite, Obsidian, Pumice.
📌 Key Point: Igneous rocks form the Earth's crust and provide essential minerals.

4. Sedimentary Rocks (Formed by Deposition and Lithification of Sediments)
  • Formed by the accumulation and compaction of sediments (fragments of rocks, minerals, and organic material).
  • Clastic Sedimentary Rocks: Made of broken rock fragments.
    • Example: Sandstone, Shale, Conglomerate.
  • Chemical Sedimentary Rocks: Formed from mineral precipitation.
    • Example: Limestone, Rock Salt.
  • Organic Sedimentary Rocks: Contain remains of plants and animals.
    • Example: Coal, Chalk.
📌 Key Point: Sedimentary rocks preserve fossils and tell us about Earth's past environments.

5. Metamorphic Rocks (Formed by Heat and Pressure on Existing Rocks)
  • Formed when igneous or sedimentary rocks undergo heat and pressure.
  • Foliated Metamorphic Rocks: Show layers or bands.
    • Example: Slate (from shale), Schist, Gneiss (from granite).
  • Non-Foliated Metamorphic Rocks: No layers, appear uniform.
    • Example: Marble (from limestone), Quartzite (from sandstone).
📌 Key Point: Metamorphic rocks are used in construction (e.g., Marble for statues and buildings).

3. Rock-Forming Minerals and Their Significance

Rock-forming minerals are the essential minerals that make up most rocks. They belong mainly to the silicate group.Common Rock-Forming Minerals:
  1. Quartz (SiO₂): Found in granite, sandstone, and metamorphic rocks.
  2. Feldspar (Orthoclase, Plagioclase): Major component of igneous rocks like granite.
  3. Mica (Biotite, Muscovite): Found in igneous and metamorphic rocks.
  4. Olivine (Mg,Fe)₂SiO₄: Found in basalt and peridotite.
  5. Amphibole (Hornblende): Present in igneous and metamorphic rocks.
  6. Calcite (CaCO₃): Main mineral in limestone and marble.
  7. Clay Minerals: Formed from weathering of feldspar, present in shale.
Significance of Rock-Forming Minerals✅ Economic Importance:
  • Quartz → Used in glass and electronics.
  • Feldspar → Used in ceramics.
  • Mica → Used in electrical insulators.
  • Calcite → Used in cement and steel production.
✅ Environmental Importance:
  • Clay minerals hold water and nutrients for plants.
  • Carbonate minerals (like calcite) help regulate Earth's carbon cycle.
✅ Geological Importance:
  • Helps geologists determine the history and formation process of rocks.
  • Used in dating rocks (e.g., Feldspar helps in radiometric dating).
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