Most hornfels are fine-grained, and while the original rocks (such as sandstone, shale, slate and limestone) may have been more or less fissile owing to the presence of bedding or cleavage planes, this structure is effaced or rendered inoperative in the hornfels. Though many hornfels show vestiges of the original bedding, they break across this as readily as along it; in fact, they tend to separate into cubical fragments rather than into thin plates. Sheet minerals may be abundant but are aligned at random.