Diamonds are known for their exceptional hardness, often considered the strongest natural material. Despite their scratch resistance, diamonds can break. How they break depends on whether force aligns with their internal atomic structure, resulting in either cleavage or fracture. This distinction is important for understanding a diamond’s durability and handling.
What is Mineral Cleavage?
Mineral cleavage refers to a mineral’s tendency to break along flat, smooth surfaces, known as cleavage planes. This property occurs due to inherent weaknesses in the mineral’s atomic structure, where chemical bonds are weaker in specific directions. When force is applied precisely along these planes, the mineral splits cleanly, creating a flat, reflective surface. Examples of minerals exhibiting distinct cleavage include mica, which splits into thin sheets, and calcite, which breaks into rhomboid shapes.
Diamonds, despite their strength, exhibit “perfect octahedral cleavage.” They have four distinct cleavage planes, parallel to an octahedron’s faces, the natural crystal habit of many rough diamonds. These planes are directions where carbon atom bonds are relatively weaker, allowing a diamond to split if struck precisely.
What is Mineral Fracture?
Mineral fracture describes the way a mineral breaks along irregular, uneven, or curved surfaces, rather than along predefined planes of weakness. This type of breakage occurs when force is applied in a direction that does not align with any inherent cleavage planes, or when the mineral’s atomic bonds are of relatively equal strength in all directions. The resulting surfaces are typically rough and jagged, lacking the smooth, flat appearance characteristic of cleavage surfaces.
Different fracture types exist. Conchoidal fracture, for instance, produces smooth, curved, shell-like surfaces, like broken glass or quartz. Other types include uneven (rough, irregular) or hackly (sharp, jagged points). Diamonds can also exhibit conchoidal fracture when struck away from their cleavage planes.
Why Diamonds Have Both
Diamonds possess both cleavage and fracture due to their unique atomic arrangement. Each carbon atom bonds strongly to four others in a repeating tetrahedral pattern, forming a rigid three-dimensional lattice. This dense network accounts for a diamond’s exceptional hardness.
However, within this strong structure, cleavage planes exist where carbon atom bonds are relatively weaker. An impact along these planes causes the diamond to cleave, resulting in a clean break. Conversely, a blow not aligned with these planes causes irregular fracture. This dual behavior shows that while diamonds are the hardest natural material, they can still break under sharp, directed impact.
Impact on Diamond Durability and Use
Both cleavage and fracture significantly impact diamond durability and use. Diamond cutters and polishers exploit cleavage, splitting rough diamonds into smaller pieces. This technique, known as cleaving, requires precise skill and knowledge of the diamond’s internal structure to avoid shattering the stone.
For consumers, understanding that diamonds can cleave or fracture is important for proper care. Despite their hardness, a sharp blow, especially to a thin girdle or pointed facet, can cause chipping or breakage. Avoid wearing diamond jewelry during activities with direct impacts, like sports or heavy labor. Regular jeweler inspections can also help identify loose settings or vulnerabilities.