Pneumatolysis is the alteration of rock or mineral crystallization affected by gaseous emanations from solidifying magma. The term was coined by Robert Bunsen in 1851.
Magmatic gases may through pneumatolysis create skarn in interaction with limestone, or greisen with granite or schist.
The term pneumatolysis has been used for various geological environments, but the essential feature of most usage has been mineral formation from a hot fluid of low density. ... The best evidence for pneumatolytic conditions is found in the presence of vapor-rich fluid inclusions, but considerable ambiguity remains and hence such evidence must be used with care. Many samples formerly thought to be of pneumatolytic origin were more likely formed from dense solutions that boiled or effervesced ...