It may also contain terpene hydrocarbons, ethers, and esters. Borneol is a bicyclic organic compound and a terpene derivative. Coniferous tree sap is a viscous liquid, that contains terpene, a volatile hydrocarbon. Secologanin is then able to proceed onto produce ipecac and terpene indole alkaloids. Verbenone is a monoterpene, to be specific a bicyclic ketone terpene. The essential oil consists of approximately 90% terpene hydrocarbons. Like the related acyclic terpene myrcene, ocimenes are unstable in air. Biosynthesis is mediated by terpene synthase. These parts of the plant contain euphorbol (a complex terpene) and other diterpene esters. Another gene cluster seems to be involved in terpene biosynthesis, most likely to produce pigments. It is biosynthesized from the common terpene precursors dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP). This higher concentration of terpene produces the muscatel flavor. Triterpenes are a type of terpene containing 30 carbon atoms.