Intro
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Cleavage and fracture describe how a mineral breaks when it is stressed. Observing break patterns helps identify minerals because some break along flat planes while others break irregularly.
• Cleavage produces flat surfaces
• Fracture produces uneven surfaces
• Important for distinguishing similar minerals
What Is Cleavage?
Cleavage occurs when a mineral breaks along flat, smooth planes.
• Breaks in predictable directions
• Reflects internal atomic structure
• Produces repeating flat surfaces
The planes form because of weak bonds within the crystal structure.
Types of Cleavage
Minerals may have different numbers and angles of cleavage planes.
Common types include:
• One direction (mica)
• Two directions at 90° (feldspar)
• Three directions at 90° (halite)
• Three directions not at 90° (calcite)
The angle between planes helps with identification.
What Is Fracture?
Fracture occurs when a mineral breaks irregularly.
• No flat surfaces
• Uneven or curved break
• Less predictable pattern
Fracture happens when there are no weak planes in the structure.
Types of Fracture
Common fracture patterns include:
• Conchoidal (smooth, curved)
• Uneven
• Fibrous
Quartz commonly shows conchoidal fracture.
Why Cleavage vs Fracture Matters
Break patterns help identify minerals that look similar.
For example:
• Quartz fractures
• Calcite shows cleavage
Even if color and luster are similar, break patterns differ.
Conclusion
Cleavage and fracture describe how minerals break under stress. Observing these patterns provides valuable clues for mineral identification.
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