Abstract: This invention is a comminution process for treating coal with a drying gas to form fractures which weaken the structure of the coal and make it easier to disintegrate mechanically, chemically or by fluid force. Another aspect of this invention is a process for treating an underground formation of coal with a dry gas for a time sufficient to form cracks and fractures in a portion of the formation in order to increase the permeability of the coal formation to the flow of fluids therethrough. Processes for in-situ combustion of the coal formation are therefore more efficient since the coal formation is more permeable to the flow of gas therethrough.