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Gemstone Dispersion: Unveiling the Rainbow within

Round Brilliant cut Diamond showing Dispersion
Image by DiamondGalaxy via Canva, Design by Gemmology Obsession

Gemstones have the power to mesmerize us with their stunning colours and captivating brilliance. One essential characteristic that contributes to their magical allure is dispersion, which is the phenomenon of breaking down white light into its spectral colours. In this blog, we will explore the captivating world of gemstone dispersion, understanding how it occurs and discovering gemstones with the highest levels of dispersion.


Understanding Gemstone Dispersion

To comprehend gemstone dispersion, we must first understand the behaviour of light. White light is a combination of all the spectral colours, each with its unique energy and wavelength. When white light encounters a dense material like a glass prism, it slows down, bends, and separates into its component colours.

Dispersion chart with prism
Image by AlexLMX via Canva, Design by Gemmology Obsession

Gemologists and mineralogists use a specific wavelength, known as "sodium light" (at 589 nm), in the yellow portion of the visible spectrum as the standard for measuring a gemstone's refractive index (RI). For instance, diamond, renowned for its exceptional brilliance, has an RI of 2.417, corresponding to sodium light.

However, in reality, the RI of most transparent materials, including Diamonds, varies for different wavelengths of light. The RI differs for violet (431 nm) and red (687 nm) wavelengths, causing them to refract to different degrees within the gemstone. As a result, when light passes through a prism, it separates into a beautiful spectrum or rainbow.


Gemstone Dispersion and Diamond

Diamond, with its extraordinary beauty, showcases one of the highest dispersions among natural transparent gem materials. Violet and blue wavelengths slow down and bend the most within the diamond, while red wavelengths slow down and bend the least. This disparity in bending angles between different wavelengths causes white light to separate into a spectrum.

Gemologists quantify the diamond's dispersion by calculating the difference in RI between the violet ray (2.451 RI) and the red ray (2.407 RI), resulting in a dispersion value of 0.044. This dispersion coefficient defines the mesmerizing fire exhibited by diamonds, creating a play of spectral colours that enchants the beholder.


Gemstones with Higher Dispersion

While diamond possesses remarkable dispersion, some simulants exhibit even higher levels of dispersion. Cubic Zirconia (CZ), for example, has a dispersion coefficient of 0.060, and Synthetic Moissanite's dispersion is even more striking at 0.104. When differentiating diamonds from these simulants, their higher dispersion becomes a vital visual clue as their rainbow colours are more prominent than those of diamonds.


Gemstone dispersion is a captivating phenomenon that enhances the beauty and allure of these precious treasures. Understanding dispersion allows us to appreciate the mesmerizing play of colours within gemstones, adding an extra dimension to their visual appeal. From the exceptional dispersion of diamonds to the remarkable dispersion found in simulants like CZ and synthetic moissanite, each gemstone presents a unique display of spectral colours. So, the next time you gaze upon a gemstone's brilliance, take a moment to admire the captivating dance of light within, bringing forth its sparkling beauty.


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