Resin is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber. Resins are also a material in nail polish. The term is also used for synthetic substances of similar properties. Resins have a very long history and are mentioned by both ancient Greek Theophrastus and ancient Roman Pliny the Elder, especially as the forms known as frankincense and myrrh. They were highly prized substances used for many purposes, especially perfumery and as incense in religious rites.