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Rock alteration or mineral crystallization effected by gaseous emanations from solidifying magma.



mineral formation by the action on the country rock of volatile compounds released from magma, chiefly superheated water vapor; of compounds of B, P, S, and As; and of the fluorides and chlorides of tin, tungsten, beryllium, and lithium. Pneumatolysis is generally most evident in strata that enclose acidic intrusions (granites). Sometimes it is evident in strata that enclose alkali and basic intrusions, as well as in pegmatites, contact-metasomatic formations, and areas of volcanic eruptions. With the plutonic recrystallization of these formations, a group of pneumatolytic mineral deposits is formed as a consequence of pneumatolysis.

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