in Chemistry, the formation of a kind of mealy powder on the surface of certain bodies. It is occasioned either by decomposition or by drying. The efflorescence which happens to cobalt and martial pyrites is of the former kind; and that observed on the crystals of soda, Glauber's salt, &c., is of the latter kind. An efflorescence is sometimes also a species of crystallization, such as the beautiful vegetations which shoot up from different saline substances. See Crystallization.

The term is used in botany to denote the time of flowering.