19. Selective Absorption
The reason gems and precious stones come in a myriad of colours is due to selective absorption. This is a property of absorbing a specific selection of the wavelength of white light as it passes through the stone. Should a stone allow the entire wavelength to pass through, it would appear colourless. If it absorbed all the wavelengths equally, the gemstone would appear black. An opaque or coloured stone is reached when certain wavelengths are absorbed while others are reflected, all of which are due to the stone’s selective absorption.
