Question

what makes a diamond shine

Answer 1

Diamonds get their brilliance from three things: reflection, refraction and dispersion. Reflection is the light that hits the diamond and is immediately bounced back up, giving it an instantaneous shine.

Answer 2

Reflection of the light is the main reason for the diamond's shine.light ray falling on the diamond is reflected multiple times inside the diamond and therefore sends light out in all directions. Actually, diamonds don't shine, they reflect.