Metamorphism can also occur in areas of stress such as faulting and folding of rock or in areas of plate tectonics such as the oceanic crust colliding into the continental crush. The principal characteristic of metamorphic changes is that they occur while the rock is solid. Texture characteristics are very important in classifying metamorphic rocks. They range from very fine grained to coarse grained minerals. A property of a rock that allows for easy breaking along parallel planes or surfaces.
Metamorphic rocks tend to break or cleave most easily along planes parallel with foliation.
Cleavage is present along planes separated by microscopic dimensions. The planes are smooth and regular. Cleavage fragments are barely visible to the naked eye. Fragments are thicker than slaty cleavage and the cleavage planes are somewhat more irregular. Cleavage in the form of flakes, clearly visible.