Final answer:
Cleavage is the property of minerals to break along planes where chemical bonds are weakest, forming cleavage planes. It is key for identifying minerals, while fracture describes irregular breakage due to the absence of weak bond planes. Defects such as line and plane defects within the crystal structure significantly affect a material's mechanical properties.
Step-by-step explanation:
The tendency to split apart along regular, well-defined planes where bonding is weakest refers to cleavage in the context of mineralogy, a sub-discipline of Chemistry. This occurs when minerals break along planes where the chemical bonds are weakest, producing flat, shiny surfaces known as cleavage planes. Minerals can have varying numbers of cleavage planes, and cleavage is an important property for identifying minerals. Recognizing whether a mineral, such as amphibole or pyroxene, contains cleavage can provide insights into the mineral's geologic history.
In contrast to cleavage, fracture describes minerals that break irregularly, which happens when there are no planes of weakness for the bonds to break cleanly. Understanding the difference between cleavage and fracture is crucial for proper mineral identification. Line defects and plane defects are imperfections in the crystal structure that can impact the mechanical properties of materials, with the former often being responsible for plastic behavior due to the movement of dislocations.