Difference Between Cleavage and Fracture

Cleavage vs. Fracture

While there are many meanings to the words cleavage and fracture, there are two definitions that are centered around geology, the study of rocks. Different rocks and minerals have different chemical structures giving them various characteristics like color, weight, density, strength, and clarity. Cleavage and fracture refer to the characteristics of rocks when they are broken from stress.

For the average human, there may be no differences in the way rocks break or are cut. However, for geologists who specialize in the field, there is a large difference in whether a rock has been fractured or suffered from cleavage. Any mineral in the world has either fractures or cleavage. Some minerals are identified merely by the way that they demonstrate cleavage or fractures.

Cleavage is the type of break that occurs along a weak portion of a mineral. If these minerals are dropped, the breaks that occur are along the weakest areas. This is cleavage. Fractures are breaks that occur when there is no weakness in a particular mineral at all, meaning that an outside source has caused the break. When a fracture occurs, there are no two pieces that are similar. All are going to be different angles and sizes. There are five basic forms of cleavage that include: one directional, two directional, three directional, cubic, and octahedral. If a mineral has one directional cleavage, it peels as in layers. “Two directional” are breaks in two directions that are joined by a right angle. Three dimensional breaks are breaks in three directions with right angles at each. Cubic cleavage is done when a mineral breaks into the shape of a perfect cube with four right angles. Octahedral cleavage is done when a mineral breaks into many pyramids and is the hardest to detect.

Like cleavage there are two types of fractures; conchoidal and non-conchoidal. Conchoidal fractures take a round shape to the break, like if a bottle is broken on the ground. These types of fractures are easy to see and very common in certain types of minerals. Non-conchoidal fractures are different in that they are at random directions and form different planes and swirls from the original structure. Like conchoidal fractures, they are easy to find in certain minerals. Minerals that commonly demonstrate signs of cleavage include: halite, mica, calcite, and feldspar. Other common minerals that are known for fracturing include quartz and obsidian.
Summary:

Cleavage and fracture are two defining characteristics of minerals studied by geologists. Cleavage is the way a break happens along a weak plane of the mineral, and fracture is the way a break happens along a strong plane of the mineral. Fractures never result in two like pieces, rather, all at different sizes, shapes, and angles.
There are two types of fractures: non-conchoidal and conchoidal. There are five types of cleavage: one directional, two directional, three directional, cubic, and octahedral.
All minerals have cleavage or fractures. Halite, mica, and calcite are susceptible to cleavage, whereas quartz and obsidian are susceptible to fractures.

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