Why do diamonds sparkle, relating to light dispersion?

Diamonds sparkle due to a process called dispersion, where light entering the diamond is split into different colours and reflected back.

When light enters a diamond, it slows down and bends, a process known as refraction. Diamonds have a high refractive index, meaning they bend light to a high degree. This is the first step in creating the sparkle we see. However, not all light is refracted equally. Different wavelengths, or colours, of light are refracted at slightly different angles. This is dispersion, and it's why we see a rainbow of colours in a diamond's sparkle, rather than just white light.

The cut of a diamond also plays a crucial role in its sparkle. A well-cut diamond has facets, or faces, that are positioned to reflect light back towards the viewer, rather than letting it escape out the sides or bottom. This is why cut is one of the 'Four Cs' (along with carat, colour, and clarity) that determine a diamond's quality and value.

The combination of high refraction, dispersion, and a good cut results in a diamond's unique sparkle. As you move the diamond, light hits different facets and is refracted and dispersed in different ways, creating a dynamic, sparkling effect. This is often referred to as a diamond's 'fire'.

In summary, the sparkle of a diamond is a result of the physical properties of the diamond itself (its high refractive index and dispersion), as well as the skill of the diamond cutter. Together, these factors create the beautiful, sparkling gemstones we value so highly.