Tree sap never form amber because resin is what turns into amber. The terms "resin" and "sap" are sometimes incorrectly used as synonyms. The fossilization process that changes resin to amber takes millions of years.
While sap flows through the tube-like tissues in a tree's vascular system, resins form at the site of a tree's injury, such as where a branch is torn from the trunk. No specific time frame for resin fossilization has yet been determined. However, most amber is found in rocks that are between 30 and 90 million years old. Sometimes, insects that were trapped in sticky resin are found in pieces of amber. Most of the amber used in jewelry comes from species of pine trees that are extinct.