A spectrum-forming crystal, also known as a PRISM, is an optical device that refracts light and splits it into its component colors. It is made up of a transparent material, usually glass or quartz, with flat surfaces that are arranged in an angular fashion. The light entering the PRISM is bent and split into its component colors, creating a spectrum of colors. This spectrum can then be used for various applications, such as analyzing the composition of a substance or creating a rainbow effect.