Amber is a fossilized substance formed after resin, a liquid produced by some trees (not synonymous with sap) hardened millions of years ago. It is prized for its glass-like appearance and the fact that organic matter is sometimes visible inside.
While we usually think of amber as a yellow-brown color, it can also be yellow, black, brown, green or blue.
As famously portrayed in the movie "Jurassic Park", animals and plants may have become trapped in the sticky resin as it collected and hardened. These specimens have allowed scientists to learn more about bygone eras.