<P> Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes . These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye . </P> <P> Cleavage forms parallel to crystallographic planes: </P> <Ul> <Li> Basal or pinacoidal cleavage occurs when there is only one cleavage plane . Graphite has basal cleavage . Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets . </Li> <Li> Cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees . Halite (or salt) has cubic cleavage, and therefore, when halite crystals are broken, it will form more cubes . </Li> <Li> Octahedral cleavage occurs when there are four cleavage planes in a crystal . Fluorite exhibits perfect octahedral cleavage . Octahedral cleavage is common for semiconductors . Diamond also has octahedral cleavage . </Li> <Li> Rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees . Calcite had rhombohedral cleavage . </Li> <Li> Prismatic cleavage occurs when there are two cleavage planes in a crystal . Spodumene exhibits prismatic cleavage . </Li> <Li> Dodecahedral cleavage occurs when there are six cleavage planes in a crystal . Sphalerite has dodecahedral cleavage . </Li> </Ul> <Li> Basal or pinacoidal cleavage occurs when there is only one cleavage plane . Graphite has basal cleavage . Mica (like muscovite or biotite) also has basal cleavage; this is why mica can be peeled into thin sheets . </Li>

What is the difference between a crystal face and cleavage plane