Difference between Fracture and Cleavage
Fracture and cleavage are two distinct types of rock properties that are crucial in understanding the behavior and structure of geological materials. While both are related to the way rocks break, they differ significantly in their mechanisms and characteristics. In this article, we will explore the difference between fracture and cleavage, highlighting their unique features and the factors that influence their formation.
Fracture
Fracture refers to the process of rock breaking along planes that do not follow the mineral grain boundaries. This type of breakage occurs when the stress applied to the rock exceeds its strength, causing it to fail. Fractures can be classified into several types based on their orientation and the forces that cause them. The most common types of fractures include:
1. Joints: These are planar fractures that do not show significant displacement along the fracture plane. Joints are typically parallel to each other and can be either open or closed.
2. Faults: Faults are fractures that show significant displacement along the fracture plane. They can be further classified into normal faults, reverse faults, and strike-slip faults, depending on the direction of movement.
3. Shear fractures: These fractures result from the application of shear stress and are characterized by a high degree of displacement along the fracture plane.
Fractures can occur in rocks of various types and are influenced by factors such as temperature, pressure, and the presence of fluids. They can be a result of tectonic forces, thermal expansion, or the presence of inclusions within the rock.
Cleavage
Cleavage, on the other hand, is a property of rocks that describes their tendency to break along planes that are parallel to the mineral grain boundaries. These planes are called cleavage planes, and they are characterized by a high degree of slip along the mineral grain boundaries. Cleavage is a common feature in foliated rocks, such as slates, schists, and gneisses.
The formation of cleavage is related to the alignment of mineral grains within the rock, which is influenced by factors such as pressure, temperature, and the presence of fluids. Cleavage planes are typically parallel to each other and can be used to identify the rock type and its geological history.
There are several types of cleavage, including:
1. Perfect cleavage: This is the highest degree of cleavage, where the rock breaks along planes that are perfectly parallel to the mineral grain boundaries.
2. Good cleavage: The rock breaks along planes that are parallel to the mineral grain boundaries, but with some degree of grain misalignment.
3. Poor cleavage: The rock breaks along planes that are not perfectly parallel to the mineral grain boundaries, resulting in a more irregular fracture.
Conclusion
In conclusion, the difference between fracture and cleavage lies in the mechanisms and characteristics of rock breakage. Fracture refers to the breaking of rocks along planes that do not follow the mineral grain boundaries, while cleavage describes the tendency of rocks to break along planes that are parallel to the mineral grain boundaries. Understanding these properties is essential for geologists to interpret the geological history and structure of rocks.
