The tendency of a stone is, to split along:
🪨 Understanding How Stones Break
The way a mineral or rock breaks is a key diagnostic property. This question asks for the specific term that describes the tendency to split along smooth, flat surfaces.
🔬 Detailed Analysis of the Options
C. Cleavage
This is the correct answer. Cleavage is the tendency of a crystalline material (a mineral) to split along definite planes of structural weakness. These planes exist because the atomic bonds are weaker in those directions. When the mineral is struck, it breaks cleanly along these planes, creating smooth, flat surfaces.
- Cause: Weaknesses in the internal atomic structure.
- Result: Predictable, flat, often shiny surfaces.
- Example: Mica has perfect cleavage in one direction, allowing it to be peeled into paper-thin sheets. Slate (a rock) has slaty cleavage, allowing it to be split into thin roofing tiles.
B. Fracture
Fracture is the term used when a mineral breaks in a direction where there is no cleavage plane. The break is irregular and not flat because the atomic bonds are of roughly equal strength in all directions. It breaks like glass.
- Cause: Atomic bonds are of equal strength in all directions.
- Result: Irregular, rough, or curved surfaces.
- Example: Quartz does not have cleavage; instead, it exhibits a conchoidal (curved, shell-like) fracture.
A. Texture
This is incorrect. Texture describes the size, shape, and arrangement of the mineral grains within a rock. It refers to how the rock looks and feels (e.g., coarse-grained, fine-grained), not how it breaks.
D. Structure
This is incorrect. Structure refers to the large-scale features of a rock mass, such as layers (stratification), folds, or faults. While a rock will certainly break along a large structural weakness like a bedding plane, the inherent tendency of the *mineral itself* to split cleanly is called cleavage.
📊 Cleavage vs. Fracture: A Key Distinction
| Property | Cleavage | Fracture |
|---|---|---|
| Definition | Tendency to break along flat planes. | Breaking in an irregular pattern. |
| Cause | Planes of weak atomic bonds. | Atomic bonds are equally strong everywhere. |
| Resulting Surface | Smooth, flat, often reflective. | Rough, uneven, or curved. |
| Example | Mica, Slate, Calcite. | Quartz, Obsidian. |
💡 Study Tips
- Cleavage = Clean: The word "cleavage" sounds like "cleave," as in a meat cleaver making a clean cut. It describes a clean, flat break.
- Fracture = Fragment: "Fracture" sounds like "fragment." It describes a rock breaking into irregular, random fragments.
- Think of Mica vs. Glass: Mica peels into perfect sheets (cleavage). Glass shatters into sharp, curved pieces (fracture).