Cleavage, in a geological context, refers to the process of separation along natural planes in rocks. This occurs when minerals within the rock break apart due to stress or pressure, creating distinct layers or fractures. Cleavage is often observed in metamorphic rocks, where the alignment of minerals results in a smooth, flat surface. In biology, cleavage describes the early stages of cell division in an embryo. After fertilization, the single cell divides into multiple smaller cells, known as blastomeres. This process is crucial for the development of multicellular organisms, as it lays the foundation for further growth and differentiation into various cell types.