Fracture
Definition
The pattern in which a mineral breaks when it doesn't break along cleavage planes. Common types include conchoidal (shell-like), uneven, and splintery.
Example
Obsidian shows conchoidal fracture, breaking with smooth, curved surfaces like broken glass.
Breaking Without Rules
While cleavage describes how a mineral breaks along lines of weakness, <strong>fracture</strong> describes how it breaks when there are *no* such lines. It is the result of applying stress to a material that has equal bond strength in all directions. Identifying the type of fracture is key for identifying minerals like quartz, obsidian, or garnet which lack cleavage.
Types of Fracture
- Conchoidal: The most famous type, marked by smooth, curved ridges like the inside of a seashell (e.g., Obsidian, Quartz).
- Uneven/Irregular: Rough and random surface (e.g., Pyrite).
- Hackly: Jagged edges with sharp points, often seen in metals (e.g., Copper, Silver).
- Splintery: Breaks into fibers or elongated splinters (e.g., Kyanite, Actinolite).
- Earthy: Crumbles like dry soil (e.g., Kaolinite).