deletions | additions       diff --git a/Introduction_Rocks_are_the_primary__.md b/Introduction_Rocks_are_the_primary__.md  index 1719272..0091036 100644  --- a/Introduction_Rocks_are_the_primary__.md  +++ b/Introduction_Rocks_are_the_primary__.md 
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Clay particles contribute, with their negative charged surfaces, to the cation exchange capacity (CEC) of the soil, reducing the leaching of positively charged nutrients like K⁺ and NH₄⁺.   Clay content correlates positively with water holding capacity and soil organic matter (SOM) content \citep{Sollins_1996}.  Moreover,the  weathering of Ca- and Mg-silicate minerals play a central role in the global carbon cycle.   The cycle, because large amounts of  Ca and Mg, released by the weathering process, will be locked up as carbonates in marine sediments \citep{Sundquist_1985}. On In  the long-term, atmospheric CO₂ is regulated by the weathering rates of these minerals, which is influenced by climate and mountain uplift \citep{Berner_2003, Raymo_1992}. The vast amounts of nutrients locked in soil mineralshas  triggered, nearly 100 years ago, the question if of wether or not  plants can actively enter tap into  this potential nutrient source \citep{HALEY_1923,TURK_1919}. Five decades later, studies appear on the role of microorganisms, including mycorrhizal fungi, in mineral weathering \citep{WEBLEY_1963,DUFF_1963,Sperber_1958,Boyle_1967,Boyle_1973}.   More recently, a publication with the provocative title `Rock eating fungi' appeared in the journal  Nature \citep{Jongmans_1997}. This publication presented evidence of, presumably mycorrhizal, fungal hyphae drilling their way (chemically and/or physically) into feldspar grains.   This paper initiated renewed interest into the topic.   A series of reviews has been published since then, covering the research up to 2009 \citep{Finlay_2009,Hoffland_2004,Landeweert_2001}.  Since 2009, more evidence of mycorrhizal weathering has been published, based on *in vitro* and microcosmbased  research. A new aspect perspective  is the effect influence  of the emergence of different types of mycorrhizal fungi during the evolution of land plants on mineral weathering rates, and thus the global carbon cycle. The gap between laboratory based studies and the real world has been bridged by a number of field based studied studies  and mathematical modeling. So far, evidence of a substantial role of mycorrhizal fungi on soil mineral weathering has been missing, while modeling studies show contrasting results.  In this chapter we briefly introduce the basics of physical and chemical weathering mechanisms, as insight in these mechanisms is of vital importance in the interpretation of results from laboratory based experiments and modeling studies.