Definitions and classification
Natural resins

Natural resins are almost exclusively of plant origin; shellac, secreted by the insect Coccus lacca, is an exception. Plant exudates harvested from living plants (harvest resins) are the subject of numerous industrial applications in a variety of fields; this is particularly true of pine resin. The industry also exploits fossil (or semi-fossil) resins derived from plants of extinct species. These resins, of which copals are the main representatives, have been chemically transformed by prolonged exposure to the soil.

• Fossil resins are resins (hard or semi-hard) collected in the ground at the site of ancient forests that have now disappeared; semi-fossil varieties are collected at the foot of the trees that produced them.

• Crop resins are recent (soft) resins harvested from living plants....