Sap from the ancient tree has formed a beautiful landscape with glowing bits in this gorgeous amber freeform. Watch it glow blue! The presence of rainbows or iridescence in amber is often attributed to the interference and diffraction of light as it interacts with the microscopic structures within the fossilized resin. Amber is formed from the resin of ancient trees, and as this resin undergoes the process of fossilization over millions of years, it can develop various internal structures.