Total internal reflection
When light passes from more denser medium to less denser medium, if the angle of incidence is more than critical angle all light reflects to the denser medium from the plane of separation according to laws of reflection. This phenomenon is known as total internal reflection.
Yes, and diamond is a medium that total internal reflection can always be found, which I learnt in my F.3 Physics in high school. You may also include the formula here if you want to talk about it.