Amber is fossilized tree resin, which has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects. Amber is used in jewelry. It has also been used as a healing agent in folk medicine.
There are five classes of amber, defined on the basis of their chemical constituents. Because it originates as soft, sticky tree resin, amber sometimes contains animal and plant material as inclusions. Amber occurring in coal seams is also called resinite, and the term ambrite is applied to that found specifically within New Zealand coal seams.
Amber is heterogeneous in composition but consists of several resinous bodies more or less soluble in alcohol, ether, and chloroform, associated with an insoluble bituminous substance. Amber is a macromolecule by free radical polymerization of several precursors in the labdane family, e.g. communic acid, communal, and biformene. These labdanes are diterpenes (C20H32) and trienes, equipping the organic skeleton with three alkene groups for polymerization. As amber matures over the years, more polymerization takes place as well as isomerization reactions, crosslinking and cyclization.
Heated above 200 °C (392 °F), amber decomposes, yielding an oil of amber, and leaves a black residue which is known as “amber colophony”, or “amber pitch”, when dissolved in oil of turpentine or in linseed oil this forms “amber varnish” or “amber lac”.