Amber is a hardened resin exuded from trees in order to protect them from predation from insects. It frequently contains traped insects and plant material.
After the raw resin becomes buried in the ground, it starts a process of polymerisation which hardens and strengthens the material. This takes a relatively long time. Immature amber is called copal, it still contains volatile compounds. Copal is sometimes used as incense; it smells nice when it is burnt; however it is not as durable as amber and the surface of the material will react with the air.
If amber is repeatedly brushed against a dry smooth fabric it will produce a static electric charge. The word electricity derives from the greek word for amber, which is elektron