Weathering
As the article states, weathering- with the aid of water as a catalyst assists or promotes alkali feldspar alteration into kaolinite by means of hydrolysis. This differs from the mechanical actions of weathering which include mass wasting by means of expansion/contraction, impact, or exfoliation. The alteration process in this case is a chemical reaction of specific rock components to dissolved ions, more pronounced by the increased acidity of the rain.