Other times the fracture is pressed so tightly together that light will flow right through the fracture. This type will show a bright, multicolored flash when light strikes it from the correct angle. Most fractures have at least a slight bit of curvature in them. Look carefully to see this. If you encounter one that is perfectly straight, that is most likely a cleavage fracture.
Gems have cleavage planes that are much like the grain of wood.
Along the cleavage plane the gem splits easily. Finding a cleavage fracture in a gem is a sign of significant weakness. The other most common type of inclusion are other minerals. These can be small bits of debris or miniature, whole crystals. Afghani peridot sometimes has clusters of tourmaline that look like flies.