Cleavage and Fracture

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Cleavage and Fracture are minerals properties that describe the way a mineral breaks when stressed. Cleavage describes the way a mineral breaks along its plane of weakness. These planes of weakness can be described as where the atomic bonding between atoms in the crystal structure is weak at those points causing the mineral break when stressed much like a stack of papers when drop will spread off in individual sheets. There are five basic types of cleavage.

                One Directional

One Directional Cleavage peels in layers much like taking individual cards off a deck. Mica is a good example of this type of cleavage.

               Two Directional

Two Directional Cleavage breaks along two directions but not at right angles. Students seem to have the hardest time describing or identifying this cleavage. A good rule of thumb to determine this type if your not sure is to eliminate the other types of cleavage which are easier sometimes to see and what is left is the two direction. Feldspar is a good example of this type of cleavage.

Three Directional Not at Right Angles

Three Directional not right angles is often very easy to see. The mineral seems to have three dimensional boxes that would break if dropped. These boxes are leaning on their sides much like a Rhombus. Calcite is a good example of this type of cleavage.

              Cubic Cleavage

Cubic Cleavage is three directional cleavage at right angles. This cleavage can be easily recognize in that in breaks into perfect squares or cubes. A good example of this type of cleavage is the mineral Halite or "Salt" as it is commonly called.

        Octahedral Cleavage

Octahedral Cleavage is complex cleavage system where two four-sided pyramids are stack on top of each other. This cleavage is often hard to see in some mineral samples containing it. A good example of this type of cleavage is the mineral Fluorite.

Fracture

Fracture is a mineral property where the atomic bonding between atoms in the crystal structure is perfect with no weakness. When these minerals are stressed they shatter making no two pieces truly the same. There are two basic types of fractures, Conchoidal and Non-Conchoidal.

         Conchoidal Fracture

Conchoidal Fractures are easy to spot. They have a circular pattern in their break are much like broken bottle glass. Obsidian is a good example of this mineral property.

          Non-Conchoidal Fracture

Non-Conchoidal Fracture minerals are also easy to identify. They have no directional cleavage planes or swirls in there structure. A good example of this is the mineral Quartz.