During folding, how are joints formed in sandstone and cleavage formed in shale?

When beds undergo folding, the fold hinge stretches and experiences tension which can create extensional joints during compression. Often the fractures will infill with a mineral precipitate, forming a vein. Due to shale being composed of platy, clay minerals, the grains will rotate and align perpendicular to the direction of applied stress. If the cleavage forms at the same time as the fold, it will be parallel to the axial plane. For both of these answers, an evolutionary diagram would be required for clarity and to display understanding of the processes.