Question

Consider statements regarding Cleavage and Fracture: Which of the statements is/are correct?

1. Cleavage occurs along parallel planes due to internal atomic structure.
2. Fracture occurs when minerals break but not through cleavage planes.
3. Irregular crystals tend to exhibit cleavage rather than fracture.

• A. 1 only
• B. None of these
• C. 2, 3
• D. 1, 2

Answer 1

Answer:

D. 1, 2

Mineral Breakage: Cleavage and Fracture

Cleavage

• Cleavage is a fundamental property of minerals that describes how they break along specific, flat planes.

• These planes are determined by the mineral's internal atomic structure. Weak bonds between atoms in certain directions lead to preferential breaking along these lines.

• Minerals can exhibit cleavage in one, two, three, or even more directions.

• Examples: Mica minerals show one direction of cleavage, producing thin, flexible sheets. Feldspars often exhibit two directions of cleavage, at or near 90 degrees. Halite (rock salt) has three directions of cleavage, resulting in cubic fragments.

Fracture

• Fracture is the term used when a mineral breaks in a way that does not follow cleavage planes.

• This occurs when the force applied to break the mineral is not aligned with the planes of weakness.

• Fracture surfaces can be irregular, uneven, or exhibit distinct patterns.

• Types of Fracture:

  • Conchoidal fracture: Smooth, curved surfaces resembling the inside of a seashell. (e.g., Quartz, Obsidian)

  • Fibrous or Splintery fracture: Breaks into needle-like or splinter-like pieces. (e.g., Asbestos)

  • Irregular or Uneven fracture: Rough, jagged surfaces. (Most common type)

Relationship between Crystal Form and Breakage

• Minerals with well-defined internal structures and weaker bonds in specific directions are more likely to exhibit cleavage.

• Irregular crystals, particularly those with amorphous or poorly ordered internal structures, are less likely to show distinct cleavage planes and may fracture more randomly.

• Crystalline structure is key to cleavage; therefore, minerals with ordered atomic arrangements will cleave, while amorphous substances will fracture.