Crystal parting occurs when minerals break along planes of structural weakness due to external stress, along twin composition planes, or along planes of weakness due to the exsolution of another mineral. Parting breaks are very similar in appearance to cleavage, but the cause is different. Cleavage occurs because of design weakness while parting results from growth defects (deviations from the basic crystallographic design). Thus, cleavage will occur in all samples of a particular mineral, while parting is only found in samples with structural defects. Examples of parting include the octahedral parting of magnetite, the rhombohedral and basal parting in corundum, and the basal parting in pyroxenes.