American Scientist

With its fiery hue, amber has been valued for millennia for ornaments. Amber pieces, often hundreds of millions of years old, are even more treasured when they entomb plants, insects or other invertebrates or, more rarely, vertebrates such as amphibians and reptiles. Occasionally, the globules contain evidence of birds or mammals, such as a feather or fur. These inclusions were trapped in ancient sticky tree resin that then hardened and polymerized over the eons to become amber.