It is apparent that these minerals all result in nature from pneumatolytic action.
These clays are produced by the decomposition of the granite by acid vapours, which are discharged after the igneous rock has solidified ("fumarole or pneumatolytic action").
These are of pneumatolytic origin (see Pneumatolysis), and have been formed by the action of vapours emanating from cooling bodies of basic eruptive rock.
The word usage examples above have been gathered from various sources to reflect current and historial usage. They do not represent the opinions of YourDictionary.com.