Question

Explain the difference between fracture and cleavage.

Short answer

Fracture leads to jagged surfaces, while cleavage creates smooth ones.

Step-by-step solution

Understanding Fracture

Fracture refers to the way a mineral breaks along irregular surfaces, often resulting in rough, jagged edges. This breakage occurs because the mineral lacks planes of weakness, so it breaks in various directions that do not form smooth or flat surfaces.

Understanding Cleavage

Cleavage is the tendency of a mineral to break along specific planes of weakness within its structure, creating smooth, flat surfaces. These planes are where the bonds holding the mineral together are weakest, allowing it to split along these specific paths.

Comparing Fracture and Cleavage

The main difference between fracture and cleavage lies in the surface created after the break. Fracture results in irregular, rough surfaces, whereas cleavage results in smooth, flat surfaces. Additionally, cleavage occurs along specific planes of weakness, while fracture does not have such defined paths.

Key concepts

Fracture

When minerals break, fracture describes how they crack and shatter in random directions, leading to jagged and uneven surfaces. Fracture happens because the internal structure of the mineral doesn't have consistent lines of weakness. This means that when force is applied, the mineral does not split in predictable patterns. Instead, fractures can lead to a variety of shapes and textures depending on the internal arrangement of atoms.
For example, some minerals display a conchoidal fracture which resembles the curved surface of a broken piece of glass or shell. Others might have fibrous or splintery fractures. This unpredictability makes fractures useful in identifying certain minerals since the pattern can give clues about the mineral's internal structure.
To observe fracture, try applying light pressure to the mineral and see how it breaks. Remember that safety is important, so ensure you do so carefully to avoid injury.

Cleavage

Cleavage in minerals describes the tendency to split along flat, smooth planes. This happens because minerals have specific planes within their crystal structures where bonding forces between atoms are weaker.
When sufficient force is applied, minerals with good cleavage will break easily along these planes, resulting in flat surfaces. The direction and number of cleavage planes are determined by the mineral's crystal lattice. For instance, mica exhibits perfect cleavage and can be peeled off into thin sheets owing to its layered structure.
Cleavage is a key identifier in mineralogy. Minerals are often classified based on their number of cleavage planes and how these planes intersect each other. To test for cleavage, try gently tapping a mineral and observe if it splits along the expected planes.

Mineral Breakage

The collective term "mineral breakage" encompasses both fracture and cleavage, describing how minerals respond to applied force. Understanding these breakage types helps in identifying minerals and determining how they can be used in various applications.
Fracture and cleavage reveal significant details about a mineral's internal structure. Fracture results in irregular shapes, providing insight into minerals lacking specific weakness planes. Cleavage, however, highlights structured weaknesses and is more predictable in terms of resulting shapes.
Knowing the difference in breakage patterns can also inform practical uses. For instance, minerals with high cleavage like talc are used for marking purposes, while those that fracture—such as quartz—are often used in jewelry because of their unique break patterns.

• Mica splits easily along one plane due to its sheet-like structure.
• Quartz, with no cleavage, breaks with a distinctive conchoidal fracture.
• Understanding mineral breakage helps in determining suitable minerals for building materials, manufacturing, and more.