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# Mechanisms of mineral weathering  The most visible aspect of weathering is the break up of rocks and minerals into smaller fragments. This so called physical weathering acts on all scales, from the erosion of complete mountain tops to micrometer scale cracks in mineral crystals. Well known mechanisms of physical weathering are thermal stress and mechanical force by freezing water and penetrating tree roots. but But  also fungal hyphae, colonizing cracks and voids in mineral grains, can produce mechanical force. They can build up high osmotic pressure in their tissues (up to 20 µN µm⁻¹). This is enough pressure to penetrate bullet proof material\cite{Howard_1991}, material \citep{Howard_1991},  and also to widen existing cracks in mineral grains and rock fragments. The results of physical weathering is an increase in mineral surface area exposed to the soil solution. Less visible is the chemical alteration or dissolution of minerals. Although in principle most primary minerals dissolve in soil solution, certain compounds accelerate the process. The most common, and by far quantitatively most important weathering agents are protons. Protons, and also hydroxide under alkaline conditions, attack the ion bindings in the mineral crystal lattice. This process is called hydrolysis (or carbonation when carbonic acid is the main proton donor). Biotic processes have a strong influence on the soil solution pH via the exudation of protons in exchange of positively charges nutrients as NH4+ and K+, the exudation of organic acids and the release of CO2 into the soil solution.