Cleavage Vs. Fracture: Detailed Comparison

The Difference Between Cleavage and Fracture

Cleavage and fracture are two different ways that minerals break, and they are crucial for identifying and understanding mineral properties. Here's a detailed comparison of the two:

Definition:

• Cleavage: The tendency of a mineral to break along flat, even surfaces that are parallel to zones of weak bonding in the crystal structure.
• Fracture: The way a mineral breaks along surfaces that are not related to its crystal structure, often resulting in irregular or uneven surfaces.

Cleavage Vs. Fracture: Detailed Comparison

Causes:

• Cleavage occurs because of the alignment of weaker bonds within the crystal lattice of the mineral. These planes of weakness correspond to planes of atoms that are less tightly bonded to each other compared to the rest of the structure.
• Fracture occurs when a mineral is subjected to stress that exceeds the strength of its bonds, but not along any particular planes of weakness. The atomic structure does not have natural planes of separation, so the break is more random.

Appearance: 

• Cleavage: Minerals that exhibit cleavage will break into pieces that have smooth, flat surfaces. These surfaces are often parallel to one another.
• Fracture: Fractured surfaces are uneven, rough, or curved, and do not follow any consistent pattern.

Predictability:

• Cleavage: Occurs in predictable and repeatable based on the mineral's crystal structure.
• Fracture: Fracture surfaces are not predictable and do not follow any particular pattern.

Consistency:

• Cleavage: The angles between cleavage planes are consistent for a given mineral and can be used for identification purposes.
• Fracture: May vary in appearance even within the same mineral sample.

Common Descriptions Terms:

• Cleavage: Described by quality (perfect, good, poor) and number of directions
• Fracture: Described by the appearance of the broken surface. Common fracture descriptions include conchoidal (shell-like, e.g., glass), hackly (sharp and jagged, e.g., some metals), and splintery (long, thin fragments, e.g., some gemstones).

Minerals Cleavage and Fracture Examples

Importance:

• Cleavage: Often a key identifying (The number and angle of cleavage planes) characteristic for many minerals.  
• Fracture: Fracture is not typically a key property used for mineral identification, although it can be helpful in some cases.

Example of Cleavage and Fracture:

• Cleavage: Common minerals that exhibit cleavage include mica (which cleaves into thin sheets), halite (which cleaves into cubes), and calcite (which cleaves into rhombohedrons).
• Fracture: Minerals that typically show fracture include quartz (conchoidal fracture), obsidian (conchoidal fracture), and pyrite (uneven or hackly fracture).

Read also:
The Streak of Minerals
Luster of Minerals: Types & Examples