Emeralds reflect light through a process known as double refraction (birefringence), meaning that light entering the crystal is split into two rays that travel at different speeds and in different directions.
This phenomenon leads to a couple of important consequences for the way an emerald appears:
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Two Refractive Indices: Because light splits into two rays, emeralds possess two refractive indices. Refractive index describes how much a ray of light bends (refracts) when entering a substance. The two rays experience differing degrees of refraction.
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Pleochroism: The differing refraction, and therefore the differing absorption, of the two rays can lead to pleochroism. This means that the emerald may exhibit different colors when viewed from different angles. Typically, in emeralds, this manifests as a green primary body color with a bluish-green secondary color.
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Visual Appearance: The combination of double refraction and pleochroism creates a rich and visually complex interaction with light that enhances the beauty of the emerald. The different ways the light rays travel and are absorbed contribute to the gem's brilliance and depth of color.
In short, emeralds don't reflect light in a simple, straightforward manner. Instead, they refract light in two different ways, which creates the potential for pleochroism, ultimately influencing the stone's unique and appealing visual qualities.
