Diamond has a critical angle of only 24.4 degrees at its surface with air. How does this explain why a diamond sparkles?

1. The critical angle for a diamond-to-air surface is only 24.4 degrees, much smaller than for materials like glass or water. 2. Light can enter a diamond freely at almost any angle, but it can only exit through a facet if it strikes that facet at less than 24.4 degrees from the normal. 3. Facets are cut specifically to make this unlikely, so light bounces internally many times before finally escaping at only a few places. 4. Because the escaping light is concentrated at those few exit points, the diamond appears to sparkle at those spots. 5. Light in a diamond actually slows down rather than speeding up, since diamond has a high index of refraction, so that option is backwards. _Source: OpenStax Physics (CC BY 4.0), Ch 16 "Mirrors and Lenses", section 16.2 Refraction_