Crystal system

Welcome to the third episode of the Mineralogy and Crystallography course! Building upon our previous discussions of mineralogy and crystals, this episode delves into the fascinating world of crystal systems. We will explore how the internal arrangement of atoms in a crystal dictates its external symmetry and overall shape. The episode will cover the seven crystal systems – cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic – and their defining characteristics. You'll learn how to identify these systems based on their symmetry elements and crystallographic axes. Understanding crystal systems is fundamental to classifying minerals and predicting their physical properties. This will lay the groundwork to discuss concepts such as the Mohs scale, silicate minerals, and other topics in the future.

Check your understanding

These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

How many crystal systems are there?

  1. 3
  2. 5
  3. 7
  4. 10
  5. 14
  6. 32

Which crystal system has the highest symmetry?

  1. Triclinic
  2. Monoclinic
  3. Cubic
  4. Hexagonal
  5. Orthorhombic
  6. Tetragonal

Which of the following defines the axes of the tetragonal system?

  1. a = b = c; α = β = γ = 90°
  2. a = b ≠ c; α = β = γ = 90°
  3. a ≠ b ≠ c; α = β = γ = 90°
  4. a = b ≠ c; α = β = 90°, γ = 120°
  5. a = b = c; α = β = γ ≠ 90°
  6. a ≠ b ≠ c; α ≠ β ≠ γ ≠ 90°

Which of the following is NOT a symmetry element used to define crystal systems?

  1. Rotation axis
  2. Mirror plane
  3. Center of symmetry
  4. Color
  5. Crystal Face
  6. Options 3 and 4

Why is understanding crystal systems important in mineralogy?

  1. It helps determine the age of a mineral.
  2. It influences a mineral's physical properties.
  3. It helps classify and identify minerals.
  4. It reveals the exact chemical composition of a mineral.
  5. Options 2 and 3
  6. It has no use

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