Frankincense is tapped from the scraggly but hardy trees by slashing the bark, which is called striping, and allowing the exuded resin to bleed out and harden. These hardened resins are called tears. There are several species and varieties of frankincense trees, each producing a slightly different type of resin. Differences in soil and climate create even more diversity of the resin, even within the same species. Boswellia sacra trees are considered unusual for their ability to grow in environments so unforgiving that they sometimes grow out of solid rock. The initial means of attachment to the rock is unknown, but is accomplished by a bulbous disk-like swelling of the trunk. This growth prevents it from being ripped from the rock during violent storms. This feature is slight or absent in trees grown in rocky soil or gravel.
The essential oil of frankincense is produced by steam distillation of the tree resin. The oil's chemical components are 75%monoterpenes, sesquiterpenes, monoterpenoles, sesquiterpenols, and ketones. It has a good balsamic sweet fragrance, while the Indian frankincense oil has a very fresh smell. Steam or hydro distilled frankincense oil does contain a number of boswellic acids (triterpenoids), which represents a method of validating the authenticity of the essential oil. The chemistry of the essential oil is mainly monoterpenes and sesquiterpenes, with small amounts of diterpenoid components being the upper limit in terms of molecular weight.