Cleavage refers to the quality of a rock’s cleavage. Some minerals have perfect cleavage, others have good cleavage, and some have poor cleavage. Minerals can be cleaved on two or three sides. If a mineral has cleavage on two sides, it has perfect cleavage on both sides.
To determine if a rock has cleaved edges or surfaces, look closely at the surface and the edges of the rock. You should note the smoothness of the cleaved edges or surfaces. You can also check if a mineral specimen has cleavage by chipping off a small piece of the specimen, but you should do this carefully so you don’t destroy the value of the specimen. If you notice any fractures, it’s likely that the cleavage is poor.
A mineral’s cleavage planes are controlled by the lattice of the crystal. Normally, the cleavage planes of a mineral are parallel to each other. If two parallel planes are found in a single rock, it’s a prismatic cleavage.
A mineral’s cleavage occurs when it splits on a plane called the pinacoidal plane. A mineral’s cleavage surface is often quite distinctive. For instance, it may look like rice terraces on a mountainside.
A cleavage can also be found on a mineral’s face. In feldspars, for example, the cleavage surface is usually adorned with fine striations that are caused by the twinning of grains. You can see these fine striations by using a hand lens, or by tilting the sample so that the cleavage surfaces reflect light.
A rock with cleavage is often cracked along its face. In addition, it may have a jagged fracture surface. If you’re unsure of whether or not a rock has cleavage, you can always break it with a rock hammer to determine its cleavage. Just remember to use a rock hammer in a safe area and use caution.
In order to identify a mineral, you must know its cleavage planes. The number of cleavage planes and the angle at which they intersect can help you identify the mineral. Cleavage angles are helpful in determining the crystal form of a mineral.
Cleavage is a characteristic of minerals that tends to break along particular planes. In mica, cleavage produces mica sheets. Similarly, cleavage in calcite produces blocky fragments shaped like a warped rectangle. In comparison, the cleavage in galena produces true cubes.
Cleavage can also refer to the quality of a mineral’s cleavage. Some minerals display cleavage in terms of their habit of forming spherical groups, drusy crystals, or stellated crystals. While most minerals show cleavage, some are broken along a plane that is flat, irregular, or otherwise irregular.