Total internal reflection (TIR) occurs at the interface of two transparent medium when the ray of light travels from a denser medium to a rarer medium
The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90°.
Total internal reflection (TIR) of light is the reflection of light within the same medium when a ray of light is incident at the interface of two medium at an angle of incidence which is greater than the critical angle for the pair of media i.e.i >i_c.
EXPLANATION:
Diamonds are known for their spectacular brilliance
The total internal reflection of light inside the diamond is the main reason for their brilliance.
For the Diamond-Air interface, the critical angle is (@ 24.4°), which is very small , therefore it is very likely to undergo total internal reflection inside it, once light enters a diamond.
Naturally found diamonds rarely exhibit the brilliance for which they are known.
The technical skill of a diamond cutter makes diamonds sparkle so brilliantly.
This is done by cutting the diamond in different angles suitably, to make sure total internal reflections occur.