Amber is fossilized tree resin that has been appreciated for its colour and natural beauty since the Neolithic. We find amber around the globe, generally in rocks that are Cretaceous or younger.
Tree resin or sap is essential to a tree. Roots take up water and nutrients, and these need to be spread throughout the tree. Sap is the viscous liquid that carries these yummy minerals and nutrients to areas where they are most needed. Tree leaves produce simple sugars that must get transported through the tree's fibres.
If some of that sap or resin gets covered and then has extreme heat and pressure applied, amber is formed.