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Another set of organic compounds with metal-complexing properties are siderophores. This type of molecules form strong bindings with especially Fe3+. They play a key role in the release and uptake of Fe into bacteria, fungi and plants \cite{Kraemer_2014}\cite{Ahmed_2014}. Primary minerals containing substantial amounts of iron, like hornblende and biotite, show enhanced dissolution rates in the presence of microbial or fungal siderophores \cite{Kalinowski_2000}\cite{Sokolova_2010}.  To understand the impact of mycorrhizal fungi, we first need to determine what is the limiting step in the dissolution process. After decades of research it is well established that under normal, far from equilibrium conditions, the rate limiting step is the formation of so called activated surface complexes. That is the complexation of weathering agents as protons or organic ligands with metals in the mineral crystal latticeFurrer\cite{Furrer_1986} lattice\cite{Furrer_1986}  \cite{Wieland_1988}. The kinetics of this step can be described by the Transition State Theory (TST)\cite{Lasaga_1984}. For a single weathering agent, its effect on dissolution rate can be described with a simple equation: R=A⋅k⋅(agent)(agent)nR=A⋅k⋅(agent)(agent)n  where R is the dissolution rate, A the mineral surface area, k the specific rate coefficient,(agent) the activity of the weathering agent, and n the reaction order. An extreme important notice is that, to our knowledge, for all tested weathering agents on all tested primary minerals, the reaction order is between 0.5 and 0.8. This has major, and counter-intuitive, consequences in understanding the impact of soil solution heterogeneity on soil scale weathering rates, see \cite{Smits_2009} and in the section 'From lab to field'.