Lecture Notes: Identifying Minerals Through Physical Characteristics

Introduction

• Objective: Understand different physical characteristics of minerals for identification purposes.
• Key Characteristics:
  • Color
  • Streak
  • Luster
  • Breakage
  • Hardness
  • Other characteristics

Color

• Description: Visible color of a mineral to the naked eye.
• Challenges: Not reliable for identification; similar colors in different minerals.
  • Examples:
    • Quartz vs. Fluorite (both purple)
    • Calcite vs. Halite (both milky white)
    • Magnetite vs. Galena (both metallic silver)
  • Note: Quartz exists in multiple colors, further complicating color-based identification.

Streak

• Description: Color of the mineral in its powdered form.
• Testing Method: Rub mineral on an unglazed ceramic streak plate (black and white tiles).
• Examples:
  • Galena: Metallic silver whole, blackish streak
  • Sulfur: Yellowish white streak
  • Azurite: Blueish streak
  • Calcite: White streak despite blue appearance

Luster

• Description: The way light reflects off the surface of the mineral.
• Types:
  • Metallic: Resembles metal, reflective (e.g., gold, silver)
  • Nonmetallic: Dull, less reflective (e.g., potassium feldspar, olivine)
  • Other types: Vitreous, pearly, silky, waxy

Breakage

• Description: How a mineral breaks apart.
• Types:
  • Cleavage: Breaks along smooth planes, predictable
    • Examples: Biotite mica (sheets), Calcite, Galena
  • Fracture: Breaks along irregular surfaces, unpredictable
    • Example: Olivine

Hardness

• Description: Resistance of a mineral to being scratched.
• Scale: Mohs scale of hardness (1 to 10)
  • Softest: Talc (1), can be scratched by a fingernail
  • Hardest: Diamond (10)
• Testing Method: Scratch test using known surfaces (e.g., glass hardness = 5.5)

Other Characteristics

• Chemical reactions:
  • Calcite fizzing with acid
  • Dolomite fizzing when powdered
• Fluorescence: Some minerals glow under UV light (e.g., Fluorite)
• Double Refraction: Visible in Calcite
• Magnetism: Magnetite
• Taste and Smell:
  • Halite tastes salty
  • Sulfur smells like rotten eggs

Conclusion

• Key Insight: All physical characteristics result from the internal arrangement of atoms in the mineral.
  • Influence properties like color, luster, streak, hardness, etc.

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