Why does a diamond sparkle?
Answer: Diamonds shine because of the full reflection of light. Because the refractive index of a diamond is very high, the critical angle of a diamond relative to air is low. The value of this critical angle is 24.5°. The surfaces of the diamond are cut in such a way that when light rays enter the diamond, the rays are repeatedly reflected completely on the different surfaces of the diamond. The reflected rays come out through only one or two surfaces. So the diamond looks very bright.