Cleavage and fracture


Cleavage and fracture

When crystals break, they can either split leaving a clean, flat face called a cleavage plane, or fracture leaving a more rough, uneven surface. We can find out more about a crystal by looking at the way it breaks.

Cleavage planes form along the weakest area of mineral's structure. If you break a mineral with a hammer it will always split along its weakest points. This is quite important, and gives some minerals a characteristic shape.

Mica, for example, has only one really good cleavage plane, it splits easily into very thin layers. Another example, calcite, will split along three cleavage planes giving a 'diamond' shape called a rhombohedron. You can see this in the example below .



set of calcite minerals



About this resource

Science topic: Minerals

Key Stage: KS2, KS3

Type: Information

Keywords: minerals, mineral properties, mineral cleavage plane, mineral fracture

mica mineral
diamond rombohedron


If a mineral's structure is equally strong in all directions it will not have any cleavage planes. Instead it will break unevenly, or fracture. There are different types of fracture. In the example below, quartz has a conchoidal (shell-shaped) fracture. Copper can have a jagged, hackly fracture.

quartz conchoidal fracture
copper mineral



Cleavage and fracture are important tools you can use to identify minerals, but you don't need to break your specimens to see this. Take a closer look, you should be able to see cleavage or fracture on any broken surface.



Learn about other properties of minerals