Final answer:
A high-quality diamond sparkles with color when illuminated by white light due to total internal reflection and dispersion. The high index of refraction causes light to separate into different colors and reflects them internally before exiting, creating a sparkling effect. Underwater, a diamond remains visible and brilliant, differentiating it from other gemstones.
Step-by-step explanation:
How Diamonds Reflect Sparkling Colors
High-quality diamonds can indeed be clear and colorless, efficiently transmitting visible wavelengths without significant absorption. However, when illuminated by white light, they can sparkle with brilliant colors. This is due to the property of total internal reflection combined with dispersion. Diamonds have a very high index of refraction, meaning light bends significantly when entering the diamond as opposed to air. As white light, which contains all colors, enters a diamond, different wavelengths (colors) of light are bent by different amounts, separating them. This separation of colors is known as dispersion. The diamond's facets act like mirrors due to total internal reflection, reflecting light internally multiple times before it exits the diamond. The light exits the diamond in various colors, creating the observed sparkle. As for the index of refraction, a diamond does not become invisible underwater because its index is higher than that of water. If a gemstone does become invisible underwater, it is likely not a diamond, which retains its brilliance due to this property.