Weathering is defined as mechanical disintegration and chemical decomposition of rocks through the actions of various elements of weather and climate.There are three major groups of weathering processes : 

• Chemical; 
• Physical or mechanical; 
• Biological weathering processes. 

Very rarely does any one of these processes ever operate completely by itself, but quite often a dominance of one process can be seen.

Further Reading:

• Chemical Weathering 
• Weathering