* Chemical Weathering: This involves changes in the chemical composition of the rock or organic matter. In the case of decaying leaves:

* Decomposition: Microorganisms like bacteria and fungi break down the complex organic molecules in leaves (cellulose, lignin, etc.) into simpler compounds. This involves chemical reactions, like oxidation and hydrolysis, that alter the structure of the leaves.

* Humification: The decomposed material forms humus, a dark, rich soil that further contributes to the chemical weathering process.

* Mechanical Weathering: This involves the physical breakdown of rocks or organic matter without changing their chemical composition. Examples include freezing/thawing, abrasion, or plant roots growing through rocks. Leaf decay doesn't involve these physical processes.

While some physical breakdown might occur during leaf decay (like fragmentation), the dominant process is the chemical breakdown by microorganisms.